libgo: update to go1.7rc3

    
    Reviewed-on: https://go-review.googlesource.com/25150

From-SVN: r238662

7 files changed, 1330 insertions, 1189 deletions

diff --git a/libgo/go/fmt/doc.go b/libgo/go/fmt/doc.go
index 4eea48e..c312914 100644
--- a/libgo/go/fmt/doc.go
+++ b/libgo/go/fmt/doc.go
@@ -62,7 +62,7 @@
 	For compound objects, the elements are printed using these rules, recursively,
 	laid out like this:
 		struct:             {field0 field1 ...}
-		array, slice:       [elem0  elem1 ...]
+		array, slice:       [elem0 elem1 ...]
 		maps:               map[key1:value1 key2:value2]
 		pointer to above:   &{}, &[], &map[]
 
@@ -95,10 +95,10 @@
 
 	For floating-point values, width sets the minimum width of the field and
 	precision sets the number of places after the decimal, if appropriate,
-	except that for %g/%G it sets the total number of digits. For example,
-	given 123.45 the format %6.2f prints 123.45 while %.4g prints 123.5.
-	The default precision for %e and %f is 6; for %g it is the smallest
-	number of digits necessary to identify the value uniquely.
+	except that for %g/%G precision sets the total number of significant
+	digits. For example, given 12.345 the format %6.3f prints 12.345 while
+	%.3g prints 12.3. The default precision for %e and %f is 6; for %g it
+	is the smallest number of digits necessary to identify the value uniquely.
 
 	For complex numbers, the width and precision apply to the two
 	components independently and the result is parenthesized, so %f applied
@@ -210,7 +210,7 @@
 		Too many arguments: %!(EXTRA type=value)
 			Printf("hi", "guys"):      hi%!(EXTRA string=guys)
 		Too few arguments: %!verb(MISSING)
-			Printf("hi%d"):            hi %!d(MISSING)
+			Printf("hi%d"):            hi%!d(MISSING)
 		Non-int for width or precision: %!(BADWIDTH) or %!(BADPREC)
 			Printf("%*s", 4.5, "hi"):  %!(BADWIDTH)hi
 			Printf("%.*s", 4.5, "hi"): %!(BADPREC)hi
diff --git a/libgo/go/fmt/export_test.go b/libgo/go/fmt/export_test.go
index 89d57ee..12d5a11 100644
--- a/libgo/go/fmt/export_test.go
+++ b/libgo/go/fmt/export_test.go
@@ -1,4 +1,4 @@
-// Copyright 2012 The Go Authors.  All rights reserved.
+// Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
diff --git a/libgo/go/fmt/fmt_test.go b/libgo/go/fmt/fmt_test.go
index ea6392f..b658236 100644
--- a/libgo/go/fmt/fmt_test.go
+++ b/libgo/go/fmt/fmt_test.go
@@ -48,13 +48,18 @@ func TestFmtInterface(t *testing.T) {
 	}
 }
 
-const b32 uint32 = 1<<32 - 1
-const b64 uint64 = 1<<64 - 1
+var (
+	NaN    = math.NaN()
+	posInf = math.Inf(1)
+	negInf = math.Inf(-1)
 
-var array = [5]int{1, 2, 3, 4, 5}
-var iarray = [4]interface{}{1, "hello", 2.5, nil}
-var slice = array[:]
-var islice = iarray[:]
+	intVar = 0
+
+	array  = [5]int{1, 2, 3, 4, 5}
+	iarray = [4]interface{}{1, "hello", 2.5, nil}
+	slice  = array[:]
+	islice = iarray[:]
+)
 
 type A struct {
 	i int
@@ -112,9 +117,11 @@ var bslice = barray[:]
 
 type byteStringer byte
 
-func (byteStringer) String() string { return "X" }
+func (byteStringer) String() string {
+	return "X"
+}
 
-var byteStringerSlice = []byteStringer{97, 98, 99, 100}
+var byteStringerSlice = []byteStringer{'h', 'e', 'l', 'l', 'o'}
 
 type byteFormatter byte
 
@@ -122,9 +129,7 @@ func (byteFormatter) Format(f State, _ rune) {
 	Fprint(f, "X")
 }
 
-var byteFormatterSlice = []byteFormatter{97, 98, 99, 100}
-
-var b byte
+var byteFormatterSlice = []byteFormatter{'h', 'e', 'l', 'l', 'o'}
 
 var fmtTests = []struct {
 	fmt string
@@ -141,6 +146,10 @@ var fmtTests = []struct {
 	{"%x", "abc", "616263"},
 	{"%x", "\xff\xf0\x0f\xff", "fff00fff"},
 	{"%X", "\xff\xf0\x0f\xff", "FFF00FFF"},
+	{"%x", "", ""},
+	{"% x", "", ""},
+	{"%#x", "", ""},
+	{"%# x", "", ""},
 	{"%x", "xyz", "78797a"},
 	{"%X", "xyz", "78797A"},
 	{"% x", "xyz", "78 79 7a"},
@@ -152,10 +161,16 @@ var fmtTests = []struct {
 
 	// basic bytes
 	{"%s", []byte("abc"), "abc"},
+	{"%s", [3]byte{'a', 'b', 'c'}, "abc"},
+	{"%s", &[3]byte{'a', 'b', 'c'}, "&abc"},
 	{"%q", []byte("abc"), `"abc"`},
 	{"%x", []byte("abc"), "616263"},
 	{"%x", []byte("\xff\xf0\x0f\xff"), "fff00fff"},
 	{"%X", []byte("\xff\xf0\x0f\xff"), "FFF00FFF"},
+	{"%x", []byte(""), ""},
+	{"% x", []byte(""), ""},
+	{"%#x", []byte(""), ""},
+	{"%# x", []byte(""), ""},
 	{"%x", []byte("xyz"), "78797a"},
 	{"%X", []byte("xyz"), "78797A"},
 	{"% x", []byte("xyz"), "78 79 7a"},
@@ -166,29 +181,112 @@ var fmtTests = []struct {
 	{"%# X", []byte("xyz"), "0X78 0X79 0X7A"},
 
 	// escaped strings
-	{"%#q", `abc`, "`abc`"},
-	{"%#q", `"`, "`\"`"},
-	{"1 %#q", `\n`, "1 `\\n`"},
-	{"2 %#q", "\n", `2 "\n"`},
-	{"%q", `"`, `"\""`},
-	{"%q", "\a\b\f\r\n\t\v", `"\a\b\f\r\n\t\v"`},
+	{"%q", "", `""`},
+	{"%#q", "", "``"},
+	{"%q", "\"", `"\""`},
+	{"%#q", "\"", "`\"`"},
+	{"%q", "`", `"` + "`" + `"`},
+	{"%#q", "`", `"` + "`" + `"`},
+	{"%q", "\n", `"\n"`},
+	{"%#q", "\n", `"\n"`},
+	{"%q", `\n`, `"\\n"`},
+	{"%#q", `\n`, "`\\n`"},
+	{"%q", "abc", `"abc"`},
+	{"%#q", "abc", "`abc`"},
+	{"%q", "日本語", `"日本語"`},
+	{"%+q", "日本語", `"\u65e5\u672c\u8a9e"`},
+	{"%#q", "日本語", "`日本語`"},
+	{"%#+q", "日本語", "`日本語`"},
+	{"%q", "\a\b\f\n\r\t\v\"\\", `"\a\b\f\n\r\t\v\"\\"`},
+	{"%+q", "\a\b\f\n\r\t\v\"\\", `"\a\b\f\n\r\t\v\"\\"`},
+	{"%#q", "\a\b\f\n\r\t\v\"\\", `"\a\b\f\n\r\t\v\"\\"`},
+	{"%#+q", "\a\b\f\n\r\t\v\"\\", `"\a\b\f\n\r\t\v\"\\"`},
+	{"%q", "☺", `"☺"`},
+	{"% q", "☺", `"☺"`}, // The space modifier should have no effect.
+	{"%+q", "☺", `"\u263a"`},
+	{"%#q", "☺", "`☺`"},
+	{"%#+q", "☺", "`☺`"},
+	{"%10q", "⌘", `       "⌘"`},
+	{"%+10q", "⌘", `  "\u2318"`},
+	{"%-10q", "⌘", `"⌘"       `},
+	{"%+-10q", "⌘", `"\u2318"  `},
+	{"%010q", "⌘", `0000000"⌘"`},
+	{"%+010q", "⌘", `00"\u2318"`},
+	{"%-010q", "⌘", `"⌘"       `}, // 0 has no effect when - is present.
+	{"%+-010q", "⌘", `"\u2318"  `},
+	{"%#8q", "\n", `    "\n"`},
+	{"%#+8q", "\r", `    "\r"`},
+	{"%#-8q", "\t", "`	`     "},
+	{"%#+-8q", "\b", `"\b"    `},
 	{"%q", "abc\xffdef", `"abc\xffdef"`},
-	{"%q", "\u263a", `"☺"`},
-	{"%+q", "\u263a", `"\u263a"`},
+	{"%+q", "abc\xffdef", `"abc\xffdef"`},
+	{"%#q", "abc\xffdef", `"abc\xffdef"`},
+	{"%#+q", "abc\xffdef", `"abc\xffdef"`},
+	// Runes that are not printable.
 	{"%q", "\U0010ffff", `"\U0010ffff"`},
+	{"%+q", "\U0010ffff", `"\U0010ffff"`},
+	{"%#q", "\U0010ffff", "`􏿿`"},
+	{"%#+q", "\U0010ffff", "`􏿿`"},
+	// Runes that are not valid.
+	{"%q", string(0x110000), `"�"`},
+	{"%+q", string(0x110000), `"\ufffd"`},
+	{"%#q", string(0x110000), "`�`"},
+	{"%#+q", string(0x110000), "`�`"},
+
+	// characters
+	{"%c", uint('x'), "x"},
+	{"%c", 0xe4, "ä"},
+	{"%c", 0x672c, "本"},
+	{"%c", '日', "日"},
+	{"%.0c", '⌘', "⌘"}, // Specifying precision should have no effect.
+	{"%3c", '⌘', "  ⌘"},
+	{"%-3c", '⌘', "⌘  "},
+	// Runes that are not printable.
+	{"%c", '\U00000e00', "\u0e00"},
+	{"%c", '\U0010ffff', "\U0010ffff"},
+	// Runes that are not valid.
+	{"%c", -1, "�"},
+	{"%c", 0xDC80, "�"},
+	{"%c", rune(0x110000), "�"},
+	{"%c", int64(0xFFFFFFFFF), "�"},
+	{"%c", uint64(0xFFFFFFFFF), "�"},
 
 	// escaped characters
-	{"%q", 'x', `'x'`},
-	{"%q", 0, `'\x00'`},
-	{"%q", '\n', `'\n'`},
-	{"%q", '\u0e00', `'\u0e00'`},         // not a printable rune.
-	{"%q", '\U000c2345', `'\U000c2345'`}, // not a printable rune.
-	{"%q", int64(0x7FFFFFFF), `%!q(int64=2147483647)`},
-	{"%q", uint64(0xFFFFFFFF), `%!q(uint64=4294967295)`},
+	{"%q", uint(0), `'\x00'`},
+	{"%+q", uint(0), `'\x00'`},
 	{"%q", '"', `'"'`},
+	{"%+q", '"', `'"'`},
 	{"%q", '\'', `'\''`},
-	{"%q", "\u263a", `"☺"`},
-	{"%+q", "\u263a", `"\u263a"`},
+	{"%+q", '\'', `'\''`},
+	{"%q", '`', "'`'"},
+	{"%+q", '`', "'`'"},
+	{"%q", 'x', `'x'`},
+	{"%+q", 'x', `'x'`},
+	{"%q", 'ÿ', `'ÿ'`},
+	{"%+q", 'ÿ', `'\u00ff'`},
+	{"%q", '\n', `'\n'`},
+	{"%+q", '\n', `'\n'`},
+	{"%q", '☺', `'☺'`},
+	{"%+q", '☺', `'\u263a'`},
+	{"% q", '☺', `'☺'`},  // The space modifier should have no effect.
+	{"%.0q", '☺', `'☺'`}, // Specifying precision should have no effect.
+	{"%10q", '⌘', `       '⌘'`},
+	{"%+10q", '⌘', `  '\u2318'`},
+	{"%-10q", '⌘', `'⌘'       `},
+	{"%+-10q", '⌘', `'\u2318'  `},
+	{"%010q", '⌘', `0000000'⌘'`},
+	{"%+010q", '⌘', `00'\u2318'`},
+	{"%-010q", '⌘', `'⌘'       `}, // 0 has no effect when - is present.
+	{"%+-010q", '⌘', `'\u2318'  `},
+	// Runes that are not printable.
+	{"%q", '\U00000e00', `'\u0e00'`},
+	{"%q", '\U0010ffff', `'\U0010ffff'`},
+	// Runes that are not valid.
+	{"%q", int32(-1), "%!q(int32=-1)"},
+	{"%q", 0xDC80, `'�'`},
+	{"%q", rune(0x110000), "%!q(int32=1114112)"},
+	{"%q", int64(0xFFFFFFFFF), "%!q(int64=68719476735)"},
+	{"%q", uint64(0xFFFFFFFFF), "%!q(uint64=68719476735)"},
 
 	// width
 	{"%5s", "abc", "  abc"},
@@ -199,57 +297,99 @@ var fmtTests = []struct {
 	{"%08q", "abc", `000"abc"`},
 	{"%5s", "abcdefghijklmnopqrstuvwxyz", "abcdefghijklmnopqrstuvwxyz"},
 	{"%.5s", "abcdefghijklmnopqrstuvwxyz", "abcde"},
+	{"%.0s", "日本語日本語", ""},
 	{"%.5s", "日本語日本語", "日本語日本"},
+	{"%.10s", "日本語日本語", "日本語日本語"},
 	{"%.5s", []byte("日本語日本語"), "日本語日本"},
 	{"%.5q", "abcdefghijklmnopqrstuvwxyz", `"abcde"`},
-	{"%.5x", "abcdefghijklmnopqrstuvwxyz", `6162636465`},
+	{"%.5x", "abcdefghijklmnopqrstuvwxyz", "6162636465"},
 	{"%.5q", []byte("abcdefghijklmnopqrstuvwxyz"), `"abcde"`},
-	{"%.5x", []byte("abcdefghijklmnopqrstuvwxyz"), `6162636465`},
+	{"%.5x", []byte("abcdefghijklmnopqrstuvwxyz"), "6162636465"},
 	{"%.3q", "日本語日本語", `"日本語"`},
 	{"%.3q", []byte("日本語日本語"), `"日本語"`},
 	{"%.1q", "日本語", `"日"`},
 	{"%.1q", []byte("日本語"), `"日"`},
-	{"%.1x", "日本語", `e6`},
-	{"%.1X", []byte("日本語"), `E6`},
+	{"%.1x", "日本語", "e6"},
+	{"%.1X", []byte("日本語"), "E6"},
 	{"%10.1q", "日本語日本語", `       "日"`},
-	{"%3c", '⌘', "  ⌘"},
-	{"%5q", '\u2026', `  '…'`},
 	{"%10v", nil, "     <nil>"},
 	{"%-10v", nil, "<nil>     "},
 
 	// integers
-	{"%d", 12345, "12345"},
-	{"%d", -12345, "-12345"},
+	{"%d", uint(12345), "12345"},
+	{"%d", int(-12345), "-12345"},
+	{"%d", ^uint8(0), "255"},
+	{"%d", ^uint16(0), "65535"},
+	{"%d", ^uint32(0), "4294967295"},
+	{"%d", ^uint64(0), "18446744073709551615"},
+	{"%d", int8(-1 << 7), "-128"},
+	{"%d", int16(-1 << 15), "-32768"},
+	{"%d", int32(-1 << 31), "-2147483648"},
+	{"%d", int64(-1 << 63), "-9223372036854775808"},
+	{"%.d", 0, ""},
+	{"%.0d", 0, ""},
+	{"%6.0d", 0, "      "},
+	{"%06.0d", 0, "      "},
+	{"% d", 12345, " 12345"},
+	{"%+d", 12345, "+12345"},
+	{"%+d", -12345, "-12345"},
+	{"%b", 7, "111"},
+	{"%b", -6, "-110"},
+	{"%b", ^uint32(0), "11111111111111111111111111111111"},
+	{"%b", ^uint64(0), "1111111111111111111111111111111111111111111111111111111111111111"},
+	{"%b", int64(-1 << 63), zeroFill("-1", 63, "")},
+	{"%o", 01234, "1234"},
+	{"%#o", 01234, "01234"},
+	{"%o", ^uint32(0), "37777777777"},
+	{"%o", ^uint64(0), "1777777777777777777777"},
+	{"%#X", 0, "0X0"},
+	{"%x", 0x12abcdef, "12abcdef"},
+	{"%X", 0x12abcdef, "12ABCDEF"},
+	{"%x", ^uint32(0), "ffffffff"},
+	{"%X", ^uint64(0), "FFFFFFFFFFFFFFFF"},
+	{"%.20b", 7, "00000000000000000111"},
 	{"%10d", 12345, "     12345"},
 	{"%10d", -12345, "    -12345"},
 	{"%+10d", 12345, "    +12345"},
 	{"%010d", 12345, "0000012345"},
 	{"%010d", -12345, "-000012345"},
-	{"%-10d", 12345, "12345     "},
-	{"%010.3d", 1, "       001"},
-	{"%010.3d", -1, "      -001"},
-	{"%+d", 12345, "+12345"},
-	{"%+d", -12345, "-12345"},
-	{"%+d", 0, "+0"},
-	{"% d", 0, " 0"},
-	{"% d", 12345, " 12345"},
-	{"%.0d", 0, ""},
-	{"%.d", 0, ""},
+	{"%20.8d", 1234, "            00001234"},
+	{"%20.8d", -1234, "           -00001234"},
+	{"%020.8d", 1234, "            00001234"},
+	{"%020.8d", -1234, "           -00001234"},
+	{"%-20.8d", 1234, "00001234            "},
+	{"%-20.8d", -1234, "-00001234           "},
+	{"%-#20.8x", 0x1234abc, "0x01234abc          "},
+	{"%-#20.8X", 0x1234abc, "0X01234ABC          "},
+	{"%-#20.8o", 01234, "00001234            "},
+
+	// Test correct f.intbuf overflow checks.
+	{"%068d", 1, zeroFill("", 68, "1")},
+	{"%068d", -1, zeroFill("-", 67, "1")},
+	{"%#.68x", 42, zeroFill("0x", 68, "2a")},
+	{"%.68d", -42, zeroFill("-", 68, "42")},
+	{"%+.68d", 42, zeroFill("+", 68, "42")},
+	{"% .68d", 42, zeroFill(" ", 68, "42")},
+	{"% +.68d", 42, zeroFill("+", 68, "42")},
 
 	// unicode format
-	{"%U", 0x1, "U+0001"},
-	{"%U", uint(0x1), "U+0001"},
-	{"%.8U", 0x2, "U+00000002"},
-	{"%U", 0x1234, "U+1234"},
-	{"%U", 0x12345, "U+12345"},
-	{"%10.6U", 0xABC, "  U+000ABC"},
-	{"%-10.6U", 0xABC, "U+000ABC  "},
+	{"%U", 0, "U+0000"},
+	{"%U", -1, "U+FFFFFFFFFFFFFFFF"},
 	{"%U", '\n', `U+000A`},
 	{"%#U", '\n', `U+000A`},
-	{"%U", 'x', `U+0078`},
-	{"%#U", 'x', `U+0078 'x'`},
+	{"%+U", 'x', `U+0078`},       // Plus flag should have no effect.
+	{"%# U", 'x', `U+0078 'x'`},  // Space flag should have no effect.
+	{"%#.2U", 'x', `U+0078 'x'`}, // Precisions below 4 should print 4 digits.
 	{"%U", '\u263a', `U+263A`},
 	{"%#U", '\u263a', `U+263A '☺'`},
+	{"%U", '\U0001D6C2', `U+1D6C2`},
+	{"%#U", '\U0001D6C2', `U+1D6C2 '𝛂'`},
+	{"%#14.6U", '⌘', "  U+002318 '⌘'"},
+	{"%#-14.6U", '⌘', "U+002318 '⌘'  "},
+	{"%#014.6U", '⌘', "  U+002318 '⌘'"},
+	{"%#-014.6U", '⌘', "U+002318 '⌘'  "},
+	{"%.68U", uint(42), zeroFill("U+", 68, "2A")},
+	{"%#.68U", '日', zeroFill("U+", 68, "65E5") + " '日'"},
 
 	// floats
 	{"%+.3e", 0.0, "+0.000e+00"},
@@ -259,6 +399,12 @@ var fmtTests = []struct {
 	{"%+.3F", float32(-1.0), "-1.000"},
 	{"%+07.2f", 1.0, "+001.00"},
 	{"%+07.2f", -1.0, "-001.00"},
+	{"%-07.2f", 1.0, "1.00   "},
+	{"%-07.2f", -1.0, "-1.00  "},
+	{"%+-07.2f", 1.0, "+1.00  "},
+	{"%+-07.2f", -1.0, "-1.00  "},
+	{"%-+07.2f", 1.0, "+1.00  "},
+	{"%-+07.2f", -1.0, "-1.00  "},
 	{"%+10.2f", +1.0, "     +1.00"},
 	{"%+10.2f", -1.0, "     -1.00"},
 	{"% .3E", -1.0, "-1.000E+00"},
@@ -270,8 +416,36 @@ var fmtTests = []struct {
 	{"% .3g", 1.0, " 1"},
 	{"%b", float32(1.0), "8388608p-23"},
 	{"%b", 1.0, "4503599627370496p-52"},
+	// Precision has no effect for binary float format.
+	{"%.4b", float32(1.0), "8388608p-23"},
+	{"%.4b", -1.0, "-4503599627370496p-52"},
+	// Test correct f.intbuf boundary checks.
+	{"%.68f", 1.0, zeroFill("1.", 68, "")},
+	{"%.68f", -1.0, zeroFill("-1.", 68, "")},
+	// float infinites and NaNs
+	{"%f", posInf, "+Inf"},
+	{"%.1f", negInf, "-Inf"},
+	{"% f", NaN, " NaN"},
+	{"%20f", posInf, "                +Inf"},
+	{"% 20F", posInf, "                 Inf"},
+	{"% 20e", negInf, "                -Inf"},
+	{"%+20E", negInf, "                -Inf"},
+	{"% +20g", negInf, "                -Inf"},
+	{"%+-20G", posInf, "+Inf                "},
+	{"%20e", NaN, "                 NaN"},
+	{"% +20E", NaN, "                +NaN"},
+	{"% -20g", NaN, " NaN                "},
+	{"%+-20G", NaN, "+NaN                "},
+	// Zero padding does not apply to infinities and NaN.
+	{"%+020e", posInf, "                +Inf"},
+	{"%-020f", negInf, "-Inf                "},
+	{"%-020E", NaN, "NaN                 "},
 
 	// complex values
+	{"%.f", 0i, "(0+0i)"},
+	{"% .f", 0i, "( 0+0i)"},
+	{"%+.f", 0i, "(+0+0i)"},
+	{"% +.f", 0i, "(+0+0i)"},
 	{"%+.3e", 0i, "(+0.000e+00+0.000e+00i)"},
 	{"%+.3f", 0i, "(+0.000+0.000i)"},
 	{"%+.3g", 0i, "(+0+0i)"},
@@ -290,35 +464,33 @@ var fmtTests = []struct {
 	{"%.3f", -1 - 2i, "(-1.000-2.000i)"},
 	{"%.3g", -1 - 2i, "(-1-2i)"},
 	{"% .3E", -1 - 2i, "(-1.000E+00-2.000E+00i)"},
+	{"%+.3g", 1 + 2i, "(+1+2i)"},
 	{"%+.3g", complex64(1 + 2i), "(+1+2i)"},
-	{"%+.3g", complex128(1 + 2i), "(+1+2i)"},
-	{"%b", complex64(1 + 2i), "(8388608p-23+8388608p-22i)"},
 	{"%b", 1 + 2i, "(4503599627370496p-52+4503599627370496p-51i)"},
-
-	// erroneous formats
-	{"", 2, "%!(EXTRA int=2)"},
-	{"%d", "hello", "%!d(string=hello)"},
+	{"%b", complex64(1 + 2i), "(8388608p-23+8388608p-22i)"},
+	// Precision has no effect for binary complex format.
+	{"%.4b", 1 + 2i, "(4503599627370496p-52+4503599627370496p-51i)"},
+	{"%.4b", complex64(1 + 2i), "(8388608p-23+8388608p-22i)"},
+	// complex infinites and NaNs
+	{"%f", complex(posInf, posInf), "(+Inf+Infi)"},
+	{"%f", complex(negInf, negInf), "(-Inf-Infi)"},
+	{"%f", complex(NaN, NaN), "(NaN+NaNi)"},
+	{"%.1f", complex(posInf, posInf), "(+Inf+Infi)"},
+	{"% f", complex(posInf, posInf), "( Inf+Infi)"},
+	{"% f", complex(negInf, negInf), "(-Inf-Infi)"},
+	{"% f", complex(NaN, NaN), "( NaN+NaNi)"},
+	{"%8e", complex(posInf, posInf), "(    +Inf    +Infi)"},
+	{"% 8E", complex(posInf, posInf), "(     Inf    +Infi)"},
+	{"%+8f", complex(negInf, negInf), "(    -Inf    -Infi)"},
+	{"% +8g", complex(negInf, negInf), "(    -Inf    -Infi)"},
+	{"% -8G", complex(NaN, NaN), "( NaN    +NaN    i)"},
+	{"%+-8b", complex(NaN, NaN), "(+NaN    +NaN    i)"},
+	// Zero padding does not apply to infinities and NaN.
+	{"%08f", complex(posInf, posInf), "(    +Inf    +Infi)"},
+	{"%-08g", complex(negInf, negInf), "(-Inf    -Inf    i)"},
+	{"%-08G", complex(NaN, NaN), "(NaN     +NaN    i)"},
 
 	// old test/fmt_test.go
-	{"%d", 1234, "1234"},
-	{"%d", -1234, "-1234"},
-	{"%d", uint(1234), "1234"},
-	{"%d", uint32(b32), "4294967295"},
-	{"%d", uint64(b64), "18446744073709551615"},
-	{"%o", 01234, "1234"},
-	{"%#o", 01234, "01234"},
-	{"%o", uint32(b32), "37777777777"},
-	{"%o", uint64(b64), "1777777777777777777777"},
-	{"%x", 0x1234abcd, "1234abcd"},
-	{"%#x", 0x1234abcd, "0x1234abcd"},
-	{"%x", b32 - 0x1234567, "fedcba98"},
-	{"%X", 0x1234abcd, "1234ABCD"},
-	{"%X", b32 - 0x1234567, "FEDCBA98"},
-	{"%#X", 0, "0X0"},
-	{"%x", b64, "ffffffffffffffff"},
-	{"%b", 7, "111"},
-	{"%b", b64, "1111111111111111111111111111111111111111111111111111111111111111"},
-	{"%b", -6, "-110"},
 	{"%e", 1.0, "1.000000e+00"},
 	{"%e", 1234.5678e3, "1.234568e+06"},
 	{"%e", 1234.5678e-8, "1.234568e-05"},
@@ -345,19 +517,6 @@ var fmtTests = []struct {
 	{"%G", -7.0, "-7"},
 	{"%G", -1e-9, "-1E-09"},
 	{"%G", float32(-1e-9), "-1E-09"},
-	{"%c", 'x', "x"},
-	{"%c", 0xe4, "ä"},
-	{"%c", 0x672c, "本"},
-	{"%c", '日', "日"},
-	{"%20.8d", 1234, "            00001234"},
-	{"%20.8d", -1234, "           -00001234"},
-	{"%20d", 1234, "                1234"},
-	{"%-20.8d", 1234, "00001234            "},
-	{"%-20.8d", -1234, "-00001234           "},
-	{"%-#20.8x", 0x1234abc, "0x01234abc          "},
-	{"%-#20.8X", 0x1234abc, "0X01234ABC          "},
-	{"%-#20.8o", 01234, "00001234            "},
-	{"%.20b", 7, "00000000000000000111"},
 	{"%20.5s", "qwertyuiop", "               qwert"},
 	{"%.5s", "qwertyuiop", "qwert"},
 	{"%-20.5s", "qwertyuiop", "qwert               "},
@@ -377,9 +536,6 @@ var fmtTests = []struct {
 	{"%g", 1.23456789e3, "1234.56789"},
 	{"%g", 1.23456789e-3, "0.00123456789"},
 	{"%g", 1.23456789e20, "1.23456789e+20"},
-	{"%20e", math.Inf(1), "                +Inf"},
-	{"%-20f", math.Inf(-1), "-Inf                "},
-	{"%20g", math.NaN(), "                 NaN"},
 
 	// arrays
 	{"%v", array, "[1 2 3 4 5]"},
@@ -396,13 +552,44 @@ var fmtTests = []struct {
 	{"%v", &slice, "&[1 2 3 4 5]"},
 	{"%v", &islice, "&[1 hello 2.5 <nil>]"},
 	{"%v", &bslice, "&[1 2 3 4 5]"},
-	{"%v", []byte{1}, "[1]"},
-	{"%v", []byte{}, "[]"},
+
+	// byte arrays and slices with %b,%c,%d,%o,%U and %v
+	{"%b", [3]byte{65, 66, 67}, "[1000001 1000010 1000011]"},
+	{"%c", [3]byte{65, 66, 67}, "[A B C]"},
+	{"%d", [3]byte{65, 66, 67}, "[65 66 67]"},
+	{"%o", [3]byte{65, 66, 67}, "[101 102 103]"},
+	{"%U", [3]byte{65, 66, 67}, "[U+0041 U+0042 U+0043]"},
+	{"%v", [3]byte{65, 66, 67}, "[65 66 67]"},
+	{"%v", [1]byte{123}, "[123]"},
+	{"%012v", []byte{}, "[]"},
+	{"%#012v", []byte{}, "[]byte{}"},
+	{"%6v", []byte{1, 11, 111}, "[     1     11    111]"},
+	{"%06v", []byte{1, 11, 111}, "[000001 000011 000111]"},
+	{"%-6v", []byte{1, 11, 111}, "[1      11     111   ]"},
+	{"%-06v", []byte{1, 11, 111}, "[1      11     111   ]"},
+	{"%#v", []byte{1, 11, 111}, "[]byte{0x1, 0xb, 0x6f}"},
+	{"%#6v", []byte{1, 11, 111}, "[]byte{   0x1,    0xb,   0x6f}"},
+	{"%#06v", []byte{1, 11, 111}, "[]byte{0x000001, 0x00000b, 0x00006f}"},
+	{"%#-6v", []byte{1, 11, 111}, "[]byte{0x1   , 0xb   , 0x6f  }"},
+	{"%#-06v", []byte{1, 11, 111}, "[]byte{0x1   , 0xb   , 0x6f  }"},
+	// f.space should and f.plus should not have an effect with %v.
+	{"% v", []byte{1, 11, 111}, "[ 1  11  111]"},
+	{"%+v", [3]byte{1, 11, 111}, "[1 11 111]"},
+	{"%# -6v", []byte{1, 11, 111}, "[]byte{ 0x1  ,  0xb  ,  0x6f }"},
+	{"%#+-6v", [3]byte{1, 11, 111}, "[3]uint8{0x1   , 0xb   , 0x6f  }"},
+	// f.space and f.plus should have an effect with %d.
+	{"% d", []byte{1, 11, 111}, "[ 1  11  111]"},
+	{"%+d", [3]byte{1, 11, 111}, "[+1 +11 +111]"},
+	{"%# -6d", []byte{1, 11, 111}, "[ 1      11     111  ]"},
+	{"%#+-6d", [3]byte{1, 11, 111}, "[+1     +11    +111  ]"},
+
+	// floates with %v
+	{"%v", 1.2345678, "1.2345678"},
+	{"%v", float32(1.2345678), "1.2345678"},
 
 	// complexes with %v
 	{"%v", 1 + 2i, "(1+2i)"},
 	{"%v", complex64(1 + 2i), "(1+2i)"},
-	{"%v", complex128(1 + 2i), "(1+2i)"},
 
 	// structs
 	{"%v", A{1, 2, "a", []int{1, 2}}, `{1 2 a [1 2]}`},
@@ -422,7 +609,7 @@ var fmtTests = []struct {
 
 	// go syntax
 	{"%#v", A{1, 2, "a", []int{1, 2}}, `fmt_test.A{i:1, j:0x2, s:"a", x:[]int{1, 2}}`},
-	{"%#v", &b, "(*uint8)(0xPTR)"},
+	{"%#v", new(byte), "(*uint8)(0xPTR)"},
 	{"%#v", TestFmtInterface, "(func(*testing.T))(0xPTR)"},
 	{"%#v", make(chan int), "(chan int)(0xPTR)"},
 	{"%#v", uint64(1<<64 - 1), "0xffffffffffffffff"},
@@ -442,8 +629,20 @@ var fmtTests = []struct {
 	{"%#v", "foo", `"foo"`},
 	{"%#v", barray, `[5]fmt_test.renamedUint8{0x1, 0x2, 0x3, 0x4, 0x5}`},
 	{"%#v", bslice, `[]fmt_test.renamedUint8{0x1, 0x2, 0x3, 0x4, 0x5}`},
-	{"%#v", []byte(nil), "[]byte(nil)"},
 	{"%#v", []int32(nil), "[]int32(nil)"},
+	{"%#v", 1.2345678, "1.2345678"},
+	{"%#v", float32(1.2345678), "1.2345678"},
+	// Only print []byte and []uint8 as type []byte if they appear at the top level.
+	{"%#v", []byte(nil), "[]byte(nil)"},
+	{"%#v", []uint8(nil), "[]byte(nil)"},
+	{"%#v", []byte{}, "[]byte{}"},
+	{"%#v", []uint8{}, "[]byte{}"},
+	{"%#v", reflect.ValueOf([]byte{}), "[]uint8{}"},
+	{"%#v", reflect.ValueOf([]uint8{}), "[]uint8{}"},
+	{"%#v", &[]byte{}, "&[]uint8{}"},
+	{"%#v", &[]byte{}, "&[]uint8{}"},
+	{"%#v", [3]byte{}, "[3]uint8{0x0, 0x0, 0x0}"},
+	{"%#v", [3]uint8{}, "[3]uint8{0x0, 0x0, 0x0}"},
 
 	// slices with other formats
 	{"%#x", []int{1, 2, 15}, `[0x1 0x2 0xf]`},
@@ -453,30 +652,61 @@ var fmtTests = []struct {
 	{"%q", []string{"a", "b"}, `["a" "b"]`},
 	{"% 02x", []byte{1}, "01"},
 	{"% 02x", []byte{1, 2, 3}, "01 02 03"},
+
 	// Padding with byte slices.
-	{"%x", []byte{}, ""},
-	{"%02x", []byte{}, "00"},
+	{"%2x", []byte{}, "  "},
+	{"%#2x", []byte{}, "  "},
 	{"% 02x", []byte{}, "00"},
-	{"%08x", []byte{0xab}, "000000ab"},
-	{"% 08x", []byte{0xab}, "000000ab"},
-	{"%08x", []byte{0xab, 0xcd}, "0000abcd"},
-	{"% 08x", []byte{0xab, 0xcd}, "000ab cd"},
+	{"%# 02x", []byte{}, "00"},
+	{"%-2x", []byte{}, "  "},
+	{"%-02x", []byte{}, "  "},
 	{"%8x", []byte{0xab}, "      ab"},
 	{"% 8x", []byte{0xab}, "      ab"},
-	{"%8x", []byte{0xab, 0xcd}, "    abcd"},
-	{"% 8x", []byte{0xab, 0xcd}, "   ab cd"},
+	{"%#8x", []byte{0xab}, "    0xab"},
+	{"%# 8x", []byte{0xab}, "    0xab"},
+	{"%08x", []byte{0xab}, "000000ab"},
+	{"% 08x", []byte{0xab}, "000000ab"},
+	{"%#08x", []byte{0xab}, "00000xab"},
+	{"%# 08x", []byte{0xab}, "00000xab"},
+	{"%10x", []byte{0xab, 0xcd}, "      abcd"},
+	{"% 10x", []byte{0xab, 0xcd}, "     ab cd"},
+	{"%#10x", []byte{0xab, 0xcd}, "    0xabcd"},
+	{"%# 10x", []byte{0xab, 0xcd}, " 0xab 0xcd"},
+	{"%010x", []byte{0xab, 0xcd}, "000000abcd"},
+	{"% 010x", []byte{0xab, 0xcd}, "00000ab cd"},
+	{"%#010x", []byte{0xab, 0xcd}, "00000xabcd"},
+	{"%# 010x", []byte{0xab, 0xcd}, "00xab 0xcd"},
+	{"%-10X", []byte{0xab}, "AB        "},
+	{"% -010X", []byte{0xab}, "AB        "},
+	{"%#-10X", []byte{0xab, 0xcd}, "0XABCD    "},
+	{"%# -010X", []byte{0xab, 0xcd}, "0XAB 0XCD "},
 	// Same for strings
-	{"%x", "", ""},
-	{"%02x", "", "00"},
+	{"%2x", "", "  "},
+	{"%#2x", "", "  "},
 	{"% 02x", "", "00"},
-	{"%08x", "\xab", "000000ab"},
-	{"% 08x", "\xab", "000000ab"},
-	{"%08x", "\xab\xcd", "0000abcd"},
-	{"% 08x", "\xab\xcd", "000ab cd"},
+	{"%# 02x", "", "00"},
+	{"%-2x", "", "  "},
+	{"%-02x", "", "  "},
 	{"%8x", "\xab", "      ab"},
 	{"% 8x", "\xab", "      ab"},
-	{"%8x", "\xab\xcd", "    abcd"},
-	{"% 8x", "\xab\xcd", "   ab cd"},
+	{"%#8x", "\xab", "    0xab"},
+	{"%# 8x", "\xab", "    0xab"},
+	{"%08x", "\xab", "000000ab"},
+	{"% 08x", "\xab", "000000ab"},
+	{"%#08x", "\xab", "00000xab"},
+	{"%# 08x", "\xab", "00000xab"},
+	{"%10x", "\xab\xcd", "      abcd"},
+	{"% 10x", "\xab\xcd", "     ab cd"},
+	{"%#10x", "\xab\xcd", "    0xabcd"},
+	{"%# 10x", "\xab\xcd", " 0xab 0xcd"},
+	{"%010x", "\xab\xcd", "000000abcd"},
+	{"% 010x", "\xab\xcd", "00000ab cd"},
+	{"%#010x", "\xab\xcd", "00000xabcd"},
+	{"%# 010x", "\xab\xcd", "00xab 0xcd"},
+	{"%-10X", "\xab", "AB        "},
+	{"% -010X", "\xab", "AB        "},
+	{"%#-10X", "\xab\xcd", "0XABCD    "},
+	{"%# -010X", "\xab\xcd", "0XAB 0XCD "},
 
 	// renamings
 	{"%v", renamedBool(true), "true"},
@@ -495,7 +725,8 @@ var fmtTests = []struct {
 	{"%x", renamedString("thing"), "7468696e67"},
 	{"%d", renamedBytes([]byte{1, 2, 15}), `[1 2 15]`},
 	{"%q", renamedBytes([]byte("hello")), `"hello"`},
-	{"%x", []renamedUint8{'a', 'b', 'c'}, "616263"},
+	{"%x", []renamedUint8{'h', 'e', 'l', 'l', 'o'}, "68656c6c6f"},
+	{"%X", []renamedUint8{'h', 'e', 'l', 'l', 'o'}, "68656C6C6F"},
 	{"%s", []renamedUint8{'h', 'e', 'l', 'l', 'o'}, "hello"},
 	{"%q", []renamedUint8{'h', 'e', 'l', 'l', 'o'}, `"hello"`},
 	{"%v", renamedFloat32(22), "22"},
@@ -513,79 +744,72 @@ var fmtTests = []struct {
 	{"%#v", S{F(7), G(8)}, "fmt_test.S{F:<v=F(7)>, G:GoString(8)}"},
 
 	// %T
+	{"%T", byte(0), "uint8"},
+	{"%T", reflect.ValueOf(nil), "reflect.Value"},
 	{"%T", (4 - 3i), "complex128"},
 	{"%T", renamedComplex128(4 - 3i), "fmt_test.renamedComplex128"},
-	{"%T", intVal, "int"},
-	{"%6T", &intVal, "  *int"},
+	{"%T", intVar, "int"},
+	{"%6T", &intVar, "  *int"},
 	{"%10T", nil, "     <nil>"},
 	{"%-10T", nil, "<nil>     "},
 
-	// %p
-	{"p0=%p", new(int), "p0=0xPTR"},
-	{"p1=%s", &pValue, "p1=String(p)"}, // String method...
-	{"p2=%p", &pValue, "p2=0xPTR"},     // ... not called with %p
-	{"p3=%p", (*int)(nil), "p3=0x0"},
-	{"p4=%#p", new(int), "p4=PTR"},
-
+	// %p with pointers
+	{"%p", (*int)(nil), "0x0"},
+	{"%#p", (*int)(nil), "0"},
+	{"%p", &intVar, "0xPTR"},
+	{"%#p", &intVar, "PTR"},
+	{"%p", &array, "0xPTR"},
+	{"%p", &slice, "0xPTR"},
+	{"%8.2p", (*int)(nil), "    0x00"},
+	{"%-20.16p", &intVar, "0xPTR  "},
 	// %p on non-pointers
 	{"%p", make(chan int), "0xPTR"},
 	{"%p", make(map[int]int), "0xPTR"},
-	{"%p", make([]int, 1), "0xPTR"},
-	{"%p", 27, "%!p(int=27)"}, // not a pointer at all
-
-	// %q on pointers
-	{"%q", (*int)(nil), "%!q(*int=<nil>)"},
-	{"%q", new(int), "%!q(*int=0xPTR)"},
-
-	// %v on pointers formats 0 as <nil>
+	{"%p", func() {}, "0xPTR"},
+	{"%p", 27, "%!p(int=27)"},  // not a pointer at all
+	{"%p", nil, "%!p(<nil>)"},  // nil on its own has no type ...
+	{"%#p", nil, "%!p(<nil>)"}, // ... and hence is not a pointer type.
+	// pointers with specified base
+	{"%b", &intVar, "PTR_b"},
+	{"%d", &intVar, "PTR_d"},
+	{"%o", &intVar, "PTR_o"},
+	{"%x", &intVar, "PTR_x"},
+	{"%X", &intVar, "PTR_X"},
+	// %v on pointers
+	{"%v", nil, "<nil>"},
+	{"%#v", nil, "<nil>"},
 	{"%v", (*int)(nil), "<nil>"},
-	{"%v", new(int), "0xPTR"},
-
-	// %d etc. pointers use specified base.
-	{"%d", new(int), "PTR_d"},
-	{"%o", new(int), "PTR_o"},
-	{"%x", new(int), "PTR_x"},
+	{"%#v", (*int)(nil), "(*int)(nil)"},
+	{"%v", &intVar, "0xPTR"},
+	{"%#v", &intVar, "(*int)(0xPTR)"},
+	{"%8.2v", (*int)(nil), "   <nil>"},
+	{"%-20.16v", &intVar, "0xPTR  "},
+	// string method on pointer
+	{"%s", &pValue, "String(p)"}, // String method...
+	{"%p", &pValue, "0xPTR"},     // ... is not called with %p.
 
 	// %d on Stringer should give integer if possible
 	{"%s", time.Time{}.Month(), "January"},
 	{"%d", time.Time{}.Month(), "1"},
 
 	// erroneous things
+	{"", nil, "%!(EXTRA <nil>)"},
+	{"", 2, "%!(EXTRA int=2)"},
+	{"no args", "hello", "no args%!(EXTRA string=hello)"},
 	{"%s %", "hello", "hello %!(NOVERB)"},
 	{"%s %.2", "hello", "hello %!(NOVERB)"},
-	{"%d", "hello", "%!d(string=hello)"},
-	{"no args", "hello", "no args%!(EXTRA string=hello)"},
-	{"%s", nil, "%!s(<nil>)"},
-	{"%T", nil, "<nil>"},
-	{"%-1", 100, "%!(NOVERB)%!(EXTRA int=100)"},
 	{"%017091901790959340919092959340919017929593813360", 0, "%!(NOVERB)%!(EXTRA int=0)"},
 	{"%184467440737095516170v", 0, "%!(NOVERB)%!(EXTRA int=0)"},
+	// Extra argument errors should format without flags set.
+	{"%010.2", "12345", "%!(NOVERB)%!(EXTRA string=12345)"},
 
 	// The "<nil>" show up because maps are printed by
 	// first obtaining a list of keys and then looking up
-	// each key.  Since NaNs can be map keys but cannot
+	// each key. Since NaNs can be map keys but cannot
 	// be fetched directly, the lookup fails and returns a
 	// zero reflect.Value, which formats as <nil>.
 	// This test is just to check that it shows the two NaNs at all.
-	{"%v", map[float64]int{math.NaN(): 1, math.NaN(): 2}, "map[NaN:<nil> NaN:<nil>]"},
-
-	// Used to crash because nByte didn't allow for a sign.
-	{"%b", int64(-1 << 63), zeroFill("-1", 63, "")},
-
-	// Used to panic.
-	{"%0100d", 1, zeroFill("", 100, "1")},
-	{"%0100d", -1, zeroFill("-", 99, "1")},
-	{"%0.100f", 1.0, zeroFill("1.", 100, "")},
-	{"%0.100f", -1.0, zeroFill("-1.", 100, "")},
-
-	// Used to panic: integer function didn't look at f.prec, f.unicode, f.width or sign.
-	{"%#.80x", 42, "0x0000000000000000000000000000000000000000000000000000000000000000000000000000002a"},
-	{"%.80U", 42, "U+0000000000000000000000000000000000000000000000000000000000000000000000000000002A"},
-	{"%#.80U", '日', "U+000000000000000000000000000000000000000000000000000000000000000000000000000065E5 '日'"},
-	{"%.65d", -44, "-00000000000000000000000000000000000000000000000000000000000000044"},
-	{"%+.65d", 44, "+00000000000000000000000000000000000000000000000000000000000000044"},
-	{"% .65d", 44, " 00000000000000000000000000000000000000000000000000000000000000044"},
-	{"%  +.65d", 44, "+00000000000000000000000000000000000000000000000000000000000000044"},
+	{"%v", map[float64]int{NaN: 1, NaN: 2}, "map[NaN:<nil> NaN:<nil>]"},
 
 	// Comparison of padding rules with C printf.
 	/*
@@ -599,14 +823,16 @@ var fmtTests = []struct {
 			"[%7.2f]",
 			"[% 7.2f]",
 			"[%+7.2f]",
+			"[% +7.2f]",
 			"[%07.2f]",
 			"[% 07.2f]",
 			"[%+07.2f]",
+			"[% +07.2f]"
 		};
 
 		int main(void) {
 			int i;
-			for(i = 0; i < 9; i++) {
+			for(i = 0; i < 11; i++) {
 				printf("%s: ", format[i]);
 				printf(format[i], 1.0);
 				printf(" ");
@@ -622,9 +848,12 @@ var fmtTests = []struct {
 			[%7.2f]: [   1.00] [  -1.00]
 			[% 7.2f]: [   1.00] [  -1.00]
 			[%+7.2f]: [  +1.00] [  -1.00]
+			[% +7.2f]: [  +1.00] [  -1.00]
 			[%07.2f]: [0001.00] [-001.00]
 			[% 07.2f]: [ 001.00] [-001.00]
 			[%+07.2f]: [+001.00] [-001.00]
+			[% +07.2f]: [+001.00] [-001.00]
+
 	*/
 	{"%.2f", 1.0, "1.00"},
 	{"%.2f", -1.0, "-1.00"},
@@ -638,26 +867,35 @@ var fmtTests = []struct {
 	{"% 7.2f", -1.0, "  -1.00"},
 	{"%+7.2f", 1.0, "  +1.00"},
 	{"%+7.2f", -1.0, "  -1.00"},
+	{"% +7.2f", 1.0, "  +1.00"},
+	{"% +7.2f", -1.0, "  -1.00"},
 	{"%07.2f", 1.0, "0001.00"},
 	{"%07.2f", -1.0, "-001.00"},
 	{"% 07.2f", 1.0, " 001.00"},
 	{"% 07.2f", -1.0, "-001.00"},
 	{"%+07.2f", 1.0, "+001.00"},
 	{"%+07.2f", -1.0, "-001.00"},
+	{"% +07.2f", 1.0, "+001.00"},
+	{"% +07.2f", -1.0, "-001.00"},
 
 	// Complex numbers: exhaustively tested in TestComplexFormatting.
 	{"%7.2f", 1 + 2i, "(   1.00  +2.00i)"},
 	{"%+07.2f", -1 - 2i, "(-001.00-002.00i)"},
-	// Zero padding does not apply to infinities.
-	{"%020f", math.Inf(-1), "                -Inf"},
-	{"%020f", math.Inf(+1), "                +Inf"},
-	{"% 020f", math.Inf(-1), "                -Inf"},
-	{"% 020f", math.Inf(+1), "                 Inf"},
-	{"%+020f", math.Inf(-1), "                -Inf"},
-	{"%+020f", math.Inf(+1), "                +Inf"},
-	{"%20f", -1.0, "           -1.000000"},
-	// Make sure we can handle very large widths.
-	{"%0100f", -1.0, zeroFill("-", 99, "1.000000")},
+
+	// Use spaces instead of zero if padding to the right.
+	{"%0-5s", "abc", "abc  "},
+	{"%-05.1f", 1.0, "1.0  "},
+
+	// float and complex formatting should not change the padding width
+	// for other elements. See issue 14642.
+	{"%06v", []interface{}{+10.0, 10}, "[000010 000010]"},
+	{"%06v", []interface{}{-10.0, 10}, "[-00010 000010]"},
+	{"%06v", []interface{}{+10.0 + 10i, 10}, "[(000010+00010i) 000010]"},
+	{"%06v", []interface{}{-10.0 + 10i, 10}, "[(-00010+00010i) 000010]"},
+
+	// integer formatting should not alter padding for other elements.
+	{"%03.6v", []interface{}{1, 2.0, "x"}, "[000001 002 00x]"},
+	{"%03.0v", []interface{}{0, 2.0, "x"}, "[    002 000]"},
 
 	// Complex fmt used to leave the plus flag set for future entries in the array
 	// causing +2+0i and +3+0i instead of 2+0i and 3+0i.
@@ -667,27 +905,6 @@ var fmtTests = []struct {
 	// Incomplete format specification caused crash.
 	{"%.", 3, "%!.(int=3)"},
 
-	// Used to panic with out-of-bounds for very large numeric representations.
-	// nByte is set to handle one bit per uint64 in %b format, with a negative number.
-	// See issue 6777.
-	{"%#064x", 1, zeroFill("0x", 64, "1")},
-	{"%#064x", -1, zeroFill("-0x", 63, "1")},
-	{"%#064b", 1, zeroFill("", 64, "1")},
-	{"%#064b", -1, zeroFill("-", 63, "1")},
-	{"%#064o", 1, zeroFill("", 64, "1")},
-	{"%#064o", -1, zeroFill("-", 63, "1")},
-	{"%#064d", 1, zeroFill("", 64, "1")},
-	{"%#064d", -1, zeroFill("-", 63, "1")},
-	// Test that we handle the crossover above the size of uint64
-	{"%#072x", 1, zeroFill("0x", 72, "1")},
-	{"%#072x", -1, zeroFill("-0x", 71, "1")},
-	{"%#072b", 1, zeroFill("", 72, "1")},
-	{"%#072b", -1, zeroFill("-", 71, "1")},
-	{"%#072o", 1, zeroFill("", 72, "1")},
-	{"%#072o", -1, zeroFill("-", 71, "1")},
-	{"%#072d", 1, zeroFill("", 72, "1")},
-	{"%#072d", -1, zeroFill("-", 71, "1")},
-
 	// Padding for complex numbers. Has been bad, then fixed, then bad again.
 	{"%+10.2f", +104.66 + 440.51i, "(   +104.66   +440.51i)"},
 	{"%+10.2f", -104.66 + 440.51i, "(   -104.66   +440.51i)"},
@@ -699,19 +916,21 @@ var fmtTests = []struct {
 	{"%+010.2f", -104.66 - 440.51i, "(-000104.66-000440.51i)"},
 
 	// []T where type T is a byte with a Stringer method.
-	{"%v", byteStringerSlice, "[X X X X]"},
-	{"%s", byteStringerSlice, "abcd"},
-	{"%q", byteStringerSlice, "\"abcd\""},
-	{"%x", byteStringerSlice, "61626364"},
-	{"%#v", byteStringerSlice, "[]fmt_test.byteStringer{0x61, 0x62, 0x63, 0x64}"},
+	{"%v", byteStringerSlice, "[X X X X X]"},
+	{"%s", byteStringerSlice, "hello"},
+	{"%q", byteStringerSlice, "\"hello\""},
+	{"%x", byteStringerSlice, "68656c6c6f"},
+	{"%X", byteStringerSlice, "68656C6C6F"},
+	{"%#v", byteStringerSlice, "[]fmt_test.byteStringer{0x68, 0x65, 0x6c, 0x6c, 0x6f}"},
 
 	// And the same for Formatter.
-	{"%v", byteFormatterSlice, "[X X X X]"},
-	{"%s", byteFormatterSlice, "abcd"},
-	{"%q", byteFormatterSlice, "\"abcd\""},
-	{"%x", byteFormatterSlice, "61626364"},
+	{"%v", byteFormatterSlice, "[X X X X X]"},
+	{"%s", byteFormatterSlice, "hello"},
+	{"%q", byteFormatterSlice, "\"hello\""},
+	{"%x", byteFormatterSlice, "68656c6c6f"},
+	{"%X", byteFormatterSlice, "68656C6C6F"},
 	// This next case seems wrong, but the docs say the Formatter wins here.
-	{"%#v", byteFormatterSlice, "[]fmt_test.byteFormatter{X, X, X, X}"},
+	{"%#v", byteFormatterSlice, "[]fmt_test.byteFormatter{X, X, X, X, X}"},
 
 	// reflect.Value handled specially in Go 1.5, making it possible to
 	// see inside non-exported fields (which cannot be accessed with Interface()).
@@ -726,6 +945,32 @@ var fmtTests = []struct {
 
 	// invalid reflect.Value doesn't crash.
 	{"%v", reflect.Value{}, "<invalid reflect.Value>"},
+	{"%v", &reflect.Value{}, "<invalid Value>"},
+	{"%v", SI{reflect.Value{}}, "{<invalid Value>}"},
+
+	// Tests to check that not supported verbs generate an error string.
+	{"%☠", nil, "%!☠(<nil>)"},
+	{"%☠", interface{}(nil), "%!☠(<nil>)"},
+	{"%☠", int(0), "%!☠(int=0)"},
+	{"%☠", uint(0), "%!☠(uint=0)"},
+	{"%☠", []byte{0, 1}, "[%!☠(uint8=0) %!☠(uint8=1)]"},
+	{"%☠", []uint8{0, 1}, "[%!☠(uint8=0) %!☠(uint8=1)]"},
+	{"%☠", [1]byte{0}, "[%!☠(uint8=0)]"},
+	{"%☠", [1]uint8{0}, "[%!☠(uint8=0)]"},
+	{"%☠", "hello", "%!☠(string=hello)"},
+	{"%☠", 1.2345678, "%!☠(float64=1.2345678)"},
+	{"%☠", float32(1.2345678), "%!☠(float32=1.2345678)"},
+	{"%☠", 1.2345678 + 1.2345678i, "%!☠(complex128=(1.2345678+1.2345678i))"},
+	{"%☠", complex64(1.2345678 + 1.2345678i), "%!☠(complex64=(1.2345678+1.2345678i))"},
+	{"%☠", &intVar, "%!☠(*int=0xPTR)"},
+	{"%☠", make(chan int), "%!☠(chan int=0xPTR)"},
+	{"%☠", func() {}, "%!☠(func()=0xPTR)"},
+	{"%☠", reflect.ValueOf(renamedInt(0)), "%!☠(fmt_test.renamedInt=0)"},
+	{"%☠", SI{renamedInt(0)}, "{%!☠(fmt_test.renamedInt=0)}"},
+	{"%☠", &[]interface{}{I(1), G(2)}, "&[%!☠(fmt_test.I=1) %!☠(fmt_test.G=2)]"},
+	{"%☠", SI{&[]interface{}{I(1), G(2)}}, "{%!☠(*[]interface {}=&[1 2])}"},
+	{"%☠", reflect.Value{}, "<invalid reflect.Value>"},
+	{"%☠", map[float64]int{NaN: 1}, "map[%!☠(float64=NaN):%!☠(<nil>)]"},
 }
 
 // zeroFill generates zero-filled strings of the specified width. The length
@@ -737,27 +982,37 @@ func zeroFill(prefix string, width int, suffix string) string {
 func TestSprintf(t *testing.T) {
 	for _, tt := range fmtTests {
 		s := Sprintf(tt.fmt, tt.val)
-		if i := strings.Index(tt.out, "PTR"); i >= 0 {
-			pattern := "PTR"
-			chars := "0123456789abcdefABCDEF"
+		i := strings.Index(tt.out, "PTR")
+		if i >= 0 && i < len(s) {
+			var pattern, chars string
 			switch {
-			case strings.HasPrefix(tt.out[i:], "PTR_d"):
-				pattern = "PTR_d"
-				chars = chars[:10]
+			case strings.HasPrefix(tt.out[i:], "PTR_b"):
+				pattern = "PTR_b"
+				chars = "01"
 			case strings.HasPrefix(tt.out[i:], "PTR_o"):
 				pattern = "PTR_o"
-				chars = chars[:8]
+				chars = "01234567"
+			case strings.HasPrefix(tt.out[i:], "PTR_d"):
+				pattern = "PTR_d"
+				chars = "0123456789"
 			case strings.HasPrefix(tt.out[i:], "PTR_x"):
 				pattern = "PTR_x"
+				chars = "0123456789abcdef"
+			case strings.HasPrefix(tt.out[i:], "PTR_X"):
+				pattern = "PTR_X"
+				chars = "0123456789ABCDEF"
+			default:
+				pattern = "PTR"
+				chars = "0123456789abcdefABCDEF"
 			}
-			j := i
-			for ; j < len(s); j++ {
-				c := s[j]
-				if !strings.ContainsRune(chars, rune(c)) {
+			p := s[:i] + pattern
+			for j := i; j < len(s); j++ {
+				if !strings.ContainsRune(chars, rune(s[j])) {
+					p += s[j:]
 					break
 				}
 			}
-			s = s[0:i] + pattern + s[j:]
+			s = p
 		}
 		if s != tt.out {
 			if _, ok := tt.val.(string); ok {
@@ -775,7 +1030,7 @@ func TestSprintf(t *testing.T) {
 // thing as if done by hand with two singleton prints.
 func TestComplexFormatting(t *testing.T) {
 	var yesNo = []bool{true, false}
-	var values = []float64{1, 0, -1, math.Inf(1), math.Inf(-1), math.NaN()}
+	var values = []float64{1, 0, -1, posInf, negInf, NaN}
 	for _, plus := range yesNo {
 		for _, zero := range yesNo {
 			for _, space := range yesNo {
@@ -869,6 +1124,14 @@ func TestReorder(t *testing.T) {
 	}
 }
 
+func BenchmarkSprintfPadding(b *testing.B) {
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("%16f", 1.0)
+		}
+	})
+}
+
 func BenchmarkSprintfEmpty(b *testing.B) {
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
@@ -885,6 +1148,22 @@ func BenchmarkSprintfString(b *testing.B) {
 	})
 }
 
+func BenchmarkSprintfTruncateString(b *testing.B) {
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("%.3s", "日本語日本語日本語")
+		}
+	})
+}
+
+func BenchmarkSprintfQuoteString(b *testing.B) {
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("%q", "日本語日本語日本語")
+		}
+	})
+}
+
 func BenchmarkSprintfInt(b *testing.B) {
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
@@ -917,6 +1196,66 @@ func BenchmarkSprintfFloat(b *testing.B) {
 	})
 }
 
+func BenchmarkSprintfComplex(b *testing.B) {
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("%f", 5.23184+5.23184i)
+		}
+	})
+}
+
+func BenchmarkSprintfBoolean(b *testing.B) {
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("%t", true)
+		}
+	})
+}
+
+func BenchmarkSprintfHexString(b *testing.B) {
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("% #x", "0123456789abcdef")
+		}
+	})
+}
+
+func BenchmarkSprintfHexBytes(b *testing.B) {
+	data := []byte("0123456789abcdef")
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("% #x", data)
+		}
+	})
+}
+
+func BenchmarkSprintfBytes(b *testing.B) {
+	data := []byte("0123456789abcdef")
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("%v", data)
+		}
+	})
+}
+
+func BenchmarkSprintfStringer(b *testing.B) {
+	stringer := I(12345)
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("%v", stringer)
+		}
+	})
+}
+
+func BenchmarkSprintfStructure(b *testing.B) {
+	s := &[]interface{}{SI{12345}, map[int]string{0: "hello"}}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			Sprintf("%#v", s)
+		}
+	})
+}
+
 func BenchmarkManyArgs(b *testing.B) {
 	b.RunParallel(func(pb *testing.PB) {
 		var buf bytes.Buffer
diff --git a/libgo/go/fmt/format.go b/libgo/go/fmt/format.go
index 517b18f..0236475 100644
--- a/libgo/go/fmt/format.go
+++ b/libgo/go/fmt/format.go
@@ -5,18 +5,13 @@
 package fmt
 
 import (
-	"math"
 	"strconv"
 	"unicode/utf8"
 )
 
 const (
-	// %b of an int64, plus a sign.
-	// Hex can add 0x and we handle it specially.
-	nByte = 65
-
-	ldigits = "0123456789abcdef"
-	udigits = "0123456789ABCDEF"
+	ldigits = "0123456789abcdefx"
+	udigits = "0123456789ABCDEFX"
 )
 
 const (
@@ -24,16 +19,6 @@ const (
 	unsigned = false
 )
 
-var padZeroBytes = make([]byte, nByte)
-var padSpaceBytes = make([]byte, nByte)
-
-func init() {
-	for i := 0; i < nByte; i++ {
-		padZeroBytes[i] = '0'
-		padSpaceBytes[i] = ' '
-	}
-}
-
 // flags placed in a separate struct for easy clearing.
 type fmtFlags struct {
 	widPresent  bool
@@ -42,8 +27,6 @@ type fmtFlags struct {
 	plus        bool
 	sharp       bool
 	space       bool
-	unicode     bool
-	uniQuote    bool // Use 'x'= prefix for %U if printable.
 	zero        bool
 
 	// For the formats %+v %#v, we set the plusV/sharpV flags
@@ -56,12 +39,16 @@ type fmtFlags struct {
 // A fmt is the raw formatter used by Printf etc.
 // It prints into a buffer that must be set up separately.
 type fmt struct {
-	intbuf [nByte]byte
-	buf    *buffer
-	// width, precision
-	wid  int
-	prec int
+	buf *buffer
+
 	fmtFlags
+
+	wid  int // width
+	prec int // precision
+
+	// intbuf is large enought to store %b of an int64 with a sign and
+	// avoids padding at the end of the struct on 32 bit architectures.
+	intbuf [68]byte
 }
 
 func (f *fmt) clearflags() {
@@ -73,176 +60,213 @@ func (f *fmt) init(buf *buffer) {
 	f.clearflags()
 }
 
-// computePadding computes left and right padding widths (only one will be non-zero).
-func (f *fmt) computePadding(width int) (padding []byte, leftWidth, rightWidth int) {
-	left := !f.minus
-	w := f.wid
-	if w < 0 {
-		left = false
-		w = -w
-	}
-	w -= width
-	if w > 0 {
-		if left && f.zero {
-			return padZeroBytes, w, 0
-		}
-		if left {
-			return padSpaceBytes, w, 0
-		} else {
-			// can't be zero padding on the right
-			return padSpaceBytes, 0, w
-		}
-	}
-	return
-}
-
 // writePadding generates n bytes of padding.
-func (f *fmt) writePadding(n int, padding []byte) {
-	for n > 0 {
-		m := n
-		if m > nByte {
-			m = nByte
-		}
-		f.buf.Write(padding[0:m])
-		n -= m
+func (f *fmt) writePadding(n int) {
+	if n <= 0 { // No padding bytes needed.
+		return
 	}
+	buf := *f.buf
+	oldLen := len(buf)
+	newLen := oldLen + n
+	// Make enough room for padding.
+	if newLen > cap(buf) {
+		buf = make(buffer, cap(buf)*2+n)
+		copy(buf, *f.buf)
+	}
+	// Decide which byte the padding should be filled with.
+	padByte := byte(' ')
+	if f.zero {
+		padByte = byte('0')
+	}
+	// Fill padding with padByte.
+	padding := buf[oldLen:newLen]
+	for i := range padding {
+		padding[i] = padByte
+	}
+	*f.buf = buf[:newLen]
 }
 
-// pad appends b to f.buf, padded on left (w > 0) or right (w < 0 or f.minus).
+// pad appends b to f.buf, padded on left (!f.minus) or right (f.minus).
 func (f *fmt) pad(b []byte) {
 	if !f.widPresent || f.wid == 0 {
 		f.buf.Write(b)
 		return
 	}
-	padding, left, right := f.computePadding(utf8.RuneCount(b))
-	if left > 0 {
-		f.writePadding(left, padding)
-	}
-	f.buf.Write(b)
-	if right > 0 {
-		f.writePadding(right, padding)
+	width := f.wid - utf8.RuneCount(b)
+	if !f.minus {
+		// left padding
+		f.writePadding(width)
+		f.buf.Write(b)
+	} else {
+		// right padding
+		f.buf.Write(b)
+		f.writePadding(width)
 	}
 }
 
-// padString appends s to buf, padded on left (w > 0) or right (w < 0 or f.minus).
+// padString appends s to f.buf, padded on left (!f.minus) or right (f.minus).
 func (f *fmt) padString(s string) {
 	if !f.widPresent || f.wid == 0 {
 		f.buf.WriteString(s)
 		return
 	}
-	padding, left, right := f.computePadding(utf8.RuneCountInString(s))
-	if left > 0 {
-		f.writePadding(left, padding)
-	}
-	f.buf.WriteString(s)
-	if right > 0 {
-		f.writePadding(right, padding)
+	width := f.wid - utf8.RuneCountInString(s)
+	if !f.minus {
+		// left padding
+		f.writePadding(width)
+		f.buf.WriteString(s)
+	} else {
+		// right padding
+		f.buf.WriteString(s)
+		f.writePadding(width)
 	}
 }
 
-var (
-	trueBytes  = []byte("true")
-	falseBytes = []byte("false")
-)
-
 // fmt_boolean formats a boolean.
 func (f *fmt) fmt_boolean(v bool) {
 	if v {
-		f.pad(trueBytes)
+		f.padString("true")
 	} else {
-		f.pad(falseBytes)
+		f.padString("false")
 	}
 }
 
-// integer; interprets prec but not wid.  Once formatted, result is sent to pad()
-// and then flags are cleared.
-func (f *fmt) integer(a int64, base uint64, signedness bool, digits string) {
-	// precision of 0 and value of 0 means "print nothing"
-	if f.precPresent && f.prec == 0 && a == 0 {
-		return
+// fmt_unicode formats a uint64 as "U+0078" or with f.sharp set as "U+0078 'x'".
+func (f *fmt) fmt_unicode(u uint64) {
+	buf := f.intbuf[0:]
+
+	// With default precision set the maximum needed buf length is 18
+	// for formatting -1 with %#U ("U+FFFFFFFFFFFFFFFF") which fits
+	// into the already allocated intbuf with a capacity of 68 bytes.
+	prec := 4
+	if f.precPresent && f.prec > 4 {
+		prec = f.prec
+		// Compute space needed for "U+" , number, " '", character, "'".
+		width := 2 + prec + 2 + utf8.UTFMax + 1
+		if width > len(buf) {
+			buf = make([]byte, width)
+		}
 	}
 
-	negative := signedness == signed && a < 0
+	// Format into buf, ending at buf[i]. Formatting numbers is easier right-to-left.
+	i := len(buf)
+
+	// For %#U we want to add a space and a quoted character at the end of the buffer.
+	if f.sharp && u <= utf8.MaxRune && strconv.IsPrint(rune(u)) {
+		i--
+		buf[i] = '\''
+		i -= utf8.RuneLen(rune(u))
+		utf8.EncodeRune(buf[i:], rune(u))
+		i--
+		buf[i] = '\''
+		i--
+		buf[i] = ' '
+	}
+	// Format the Unicode code point u as a hexadecimal number.
+	for u >= 16 {
+		i--
+		buf[i] = udigits[u&0xF]
+		prec--
+		u >>= 4
+	}
+	i--
+	buf[i] = udigits[u]
+	prec--
+	// Add zeros in front of the number until requested precision is reached.
+	for prec > 0 {
+		i--
+		buf[i] = '0'
+		prec--
+	}
+	// Add a leading "U+".
+	i--
+	buf[i] = '+'
+	i--
+	buf[i] = 'U'
+
+	oldZero := f.zero
+	f.zero = false
+	f.pad(buf[i:])
+	f.zero = oldZero
+}
+
+// fmt_integer formats signed and unsigned integers.
+func (f *fmt) fmt_integer(u uint64, base int, isSigned bool, digits string) {
+	negative := isSigned && int64(u) < 0
 	if negative {
-		a = -a
+		u = -u
 	}
 
-	var buf []byte = f.intbuf[0:]
-	if f.widPresent || f.precPresent || f.plus || f.space {
-		width := f.wid + f.prec // Only one will be set, both are positive; this provides the maximum.
-		if base == 16 && f.sharp {
-			// Also adds "0x".
-			width += 2
-		}
-		if f.unicode {
-			// Also adds "U+".
-			width += 2
-			if f.uniQuote {
-				// Also adds " 'x'".
-				width += 1 + 1 + utf8.UTFMax + 1
-			}
-		}
-		if negative || f.plus || f.space {
-			width++
-		}
-		if width > nByte {
+	buf := f.intbuf[0:]
+	// The already allocated f.intbuf with a capacity of 68 bytes
+	// is large enough for integer formatting when no precision or width is set.
+	if f.widPresent || f.precPresent {
+		// Account 3 extra bytes for possible addition of a sign and "0x".
+		width := 3 + f.wid + f.prec // wid and prec are always positive.
+		if width > len(buf) {
 			// We're going to need a bigger boat.
 			buf = make([]byte, width)
 		}
 	}
 
-	// two ways to ask for extra leading zero digits: %.3d or %03d.
-	// apparently the first cancels the second.
+	// Two ways to ask for extra leading zero digits: %.3d or %03d.
+	// If both are specified the f.zero flag is ignored and
+	// padding with spaces is used instead.
 	prec := 0
 	if f.precPresent {
 		prec = f.prec
-		f.zero = false
-	} else if f.zero && f.widPresent && !f.minus && f.wid > 0 {
+		// Precision of 0 and value of 0 means "print nothing" but padding.
+		if prec == 0 && u == 0 {
+			oldZero := f.zero
+			f.zero = false
+			f.writePadding(f.wid)
+			f.zero = oldZero
+			return
+		}
+	} else if f.zero && f.widPresent {
 		prec = f.wid
 		if negative || f.plus || f.space {
 			prec-- // leave room for sign
 		}
 	}
 
-	// format a into buf, ending at buf[i].  (printing is easier right-to-left.)
-	// a is made into unsigned ua.  we could make things
-	// marginally faster by splitting the 32-bit case out into a separate
-	// block but it's not worth the duplication, so ua has 64 bits.
+	// Because printing is easier right-to-left: format u into buf, ending at buf[i].
+	// We could make things marginally faster by splitting the 32-bit case out
+	// into a separate block but it's not worth the duplication, so u has 64 bits.
 	i := len(buf)
-	ua := uint64(a)
-	// use constants for the division and modulo for more efficient code.
-	// switch cases ordered by popularity.
+	// Use constants for the division and modulo for more efficient code.
+	// Switch cases ordered by popularity.
 	switch base {
 	case 10:
-		for ua >= 10 {
+		for u >= 10 {
 			i--
-			next := ua / 10
-			buf[i] = byte('0' + ua - next*10)
-			ua = next
+			next := u / 10
+			buf[i] = byte('0' + u - next*10)
+			u = next
 		}
 	case 16:
-		for ua >= 16 {
+		for u >= 16 {
 			i--
-			buf[i] = digits[ua&0xF]
-			ua >>= 4
+			buf[i] = digits[u&0xF]
+			u >>= 4
 		}
 	case 8:
-		for ua >= 8 {
+		for u >= 8 {
 			i--
-			buf[i] = byte('0' + ua&7)
-			ua >>= 3
+			buf[i] = byte('0' + u&7)
+			u >>= 3
 		}
 	case 2:
-		for ua >= 2 {
+		for u >= 2 {
 			i--
-			buf[i] = byte('0' + ua&1)
-			ua >>= 1
+			buf[i] = byte('0' + u&1)
+			u >>= 1
 		}
 	default:
 		panic("fmt: unknown base; can't happen")
 	}
 	i--
-	buf[i] = digits[ua]
+	buf[i] = digits[u]
 	for i > 0 && prec > len(buf)-i {
 		i--
 		buf[i] = '0'
@@ -257,18 +281,13 @@ func (f *fmt) integer(a int64, base uint64, signedness bool, digits string) {
 				buf[i] = '0'
 			}
 		case 16:
+			// Add a leading 0x or 0X.
 			i--
-			buf[i] = 'x' + digits[10] - 'a'
+			buf[i] = digits[16]
 			i--
 			buf[i] = '0'
 		}
 	}
-	if f.unicode {
-		i--
-		buf[i] = '+'
-		i--
-		buf[i] = 'U'
-	}
 
 	if negative {
 		i--
@@ -281,36 +300,23 @@ func (f *fmt) integer(a int64, base uint64, signedness bool, digits string) {
 		buf[i] = ' '
 	}
 
-	// If we want a quoted char for %#U, move the data up to make room.
-	if f.unicode && f.uniQuote && a >= 0 && a <= utf8.MaxRune && strconv.IsPrint(rune(a)) {
-		runeWidth := utf8.RuneLen(rune(a))
-		width := 1 + 1 + runeWidth + 1 // space, quote, rune, quote
-		copy(buf[i-width:], buf[i:])   // guaranteed to have enough room.
-		i -= width
-		// Now put " 'x'" at the end.
-		j := len(buf) - width
-		buf[j] = ' '
-		j++
-		buf[j] = '\''
-		j++
-		utf8.EncodeRune(buf[j:], rune(a))
-		j += runeWidth
-		buf[j] = '\''
-	}
-
+	// Left padding with zeros has already been handled like precision earlier
+	// or the f.zero flag is ignored due to an explicitly set precision.
+	oldZero := f.zero
+	f.zero = false
 	f.pad(buf[i:])
+	f.zero = oldZero
 }
 
 // truncate truncates the string to the specified precision, if present.
 func (f *fmt) truncate(s string) string {
-	if f.precPresent && f.prec < utf8.RuneCountInString(s) {
+	if f.precPresent {
 		n := f.prec
 		for i := range s {
-			if n == 0 {
-				s = s[:i]
-				break
-			}
 			n--
+			if n < 0 {
+				return s[:i]
+			}
 		}
 	}
 	return s
@@ -324,212 +330,169 @@ func (f *fmt) fmt_s(s string) {
 
 // fmt_sbx formats a string or byte slice as a hexadecimal encoding of its bytes.
 func (f *fmt) fmt_sbx(s string, b []byte, digits string) {
-	n := len(b)
+	length := len(b)
 	if b == nil {
-		n = len(s)
+		// No byte slice present. Assume string s should be encoded.
+		length = len(s)
+	}
+	// Set length to not process more bytes than the precision demands.
+	if f.precPresent && f.prec < length {
+		length = f.prec
+	}
+	// Compute width of the encoding taking into account the f.sharp and f.space flag.
+	width := 2 * length
+	if width > 0 {
+		if f.space {
+			// Each element encoded by two hexadecimals will get a leading 0x or 0X.
+			if f.sharp {
+				width *= 2
+			}
+			// Elements will be separated by a space.
+			width += length - 1
+		} else if f.sharp {
+			// Only a leading 0x or 0X will be added for the whole string.
+			width += 2
+		}
+	} else { // The byte slice or string that should be encoded is empty.
+		if f.widPresent {
+			f.writePadding(f.wid)
+		}
+		return
+	}
+	// Handle padding to the left.
+	if f.widPresent && f.wid > width && !f.minus {
+		f.writePadding(f.wid - width)
 	}
-	x := digits[10] - 'a' + 'x'
-	// TODO: Avoid buffer by pre-padding.
-	var buf []byte
-	for i := 0; i < n; i++ {
-		if i > 0 && f.space {
+	// Write the encoding directly into the output buffer.
+	buf := *f.buf
+	if f.sharp {
+		// Add leading 0x or 0X.
+		buf = append(buf, '0', digits[16])
+	}
+	var c byte
+	for i := 0; i < length; i++ {
+		if f.space && i > 0 {
+			// Separate elements with a space.
 			buf = append(buf, ' ')
+			if f.sharp {
+				// Add leading 0x or 0X for each element.
+				buf = append(buf, '0', digits[16])
+			}
 		}
-		if f.sharp && (f.space || i == 0) {
-			buf = append(buf, '0', x)
-		}
-		var c byte
-		if b == nil {
-			c = s[i]
+		if b != nil {
+			c = b[i] // Take a byte from the input byte slice.
 		} else {
-			c = b[i]
+			c = s[i] // Take a byte from the input string.
 		}
+		// Encode each byte as two hexadecimal digits.
 		buf = append(buf, digits[c>>4], digits[c&0xF])
 	}
-	f.pad(buf)
+	*f.buf = buf
+	// Handle padding to the right.
+	if f.widPresent && f.wid > width && f.minus {
+		f.writePadding(f.wid - width)
+	}
 }
 
 // fmt_sx formats a string as a hexadecimal encoding of its bytes.
 func (f *fmt) fmt_sx(s, digits string) {
-	if f.precPresent && f.prec < len(s) {
-		s = s[:f.prec]
-	}
 	f.fmt_sbx(s, nil, digits)
 }
 
 // fmt_bx formats a byte slice as a hexadecimal encoding of its bytes.
 func (f *fmt) fmt_bx(b []byte, digits string) {
-	if f.precPresent && f.prec < len(b) {
-		b = b[:f.prec]
-	}
 	f.fmt_sbx("", b, digits)
 }
 
 // fmt_q formats a string as a double-quoted, escaped Go string constant.
+// If f.sharp is set a raw (backquoted) string may be returned instead
+// if the string does not contain any control characters other than tab.
 func (f *fmt) fmt_q(s string) {
 	s = f.truncate(s)
-	var quoted string
 	if f.sharp && strconv.CanBackquote(s) {
-		quoted = "`" + s + "`"
+		f.padString("`" + s + "`")
+		return
+	}
+	buf := f.intbuf[:0]
+	if f.plus {
+		f.pad(strconv.AppendQuoteToASCII(buf, s))
 	} else {
-		if f.plus {
-			quoted = strconv.QuoteToASCII(s)
-		} else {
-			quoted = strconv.Quote(s)
-		}
+		f.pad(strconv.AppendQuote(buf, s))
 	}
-	f.padString(quoted)
 }
 
-// fmt_qc formats the integer as a single-quoted, escaped Go character constant.
+// fmt_c formats an integer as a Unicode character.
 // If the character is not valid Unicode, it will print '\ufffd'.
-func (f *fmt) fmt_qc(c int64) {
-	var quoted []byte
+func (f *fmt) fmt_c(c uint64) {
+	r := rune(c)
+	if c > utf8.MaxRune {
+		r = utf8.RuneError
+	}
+	buf := f.intbuf[:0]
+	w := utf8.EncodeRune(buf[:utf8.UTFMax], r)
+	f.pad(buf[:w])
+}
+
+// fmt_qc formats an integer as a single-quoted, escaped Go character constant.
+// If the character is not valid Unicode, it will print '\ufffd'.
+func (f *fmt) fmt_qc(c uint64) {
+	r := rune(c)
+	if c > utf8.MaxRune {
+		r = utf8.RuneError
+	}
+	buf := f.intbuf[:0]
 	if f.plus {
-		quoted = strconv.AppendQuoteRuneToASCII(f.intbuf[0:0], rune(c))
+		f.pad(strconv.AppendQuoteRuneToASCII(buf, r))
 	} else {
-		quoted = strconv.AppendQuoteRune(f.intbuf[0:0], rune(c))
+		f.pad(strconv.AppendQuoteRune(buf, r))
 	}
-	f.pad(quoted)
 }
 
-// floating-point
-
-func doPrec(f *fmt, def int) int {
+// fmt_float formats a float64. It assumes that verb is a valid format specifier
+// for strconv.AppendFloat and therefore fits into a byte.
+func (f *fmt) fmt_float(v float64, size int, verb rune, prec int) {
+	// Explicit precision in format specifier overrules default precision.
 	if f.precPresent {
-		return f.prec
+		prec = f.prec
 	}
-	return def
-}
-
-// formatFloat formats a float64; it is an efficient equivalent to  f.pad(strconv.FormatFloat()...).
-func (f *fmt) formatFloat(v float64, verb byte, prec, n int) {
 	// Format number, reserving space for leading + sign if needed.
-	num := strconv.AppendFloat(f.intbuf[0:1], v, verb, prec, n)
+	num := strconv.AppendFloat(f.intbuf[:1], v, byte(verb), prec, size)
 	if num[1] == '-' || num[1] == '+' {
 		num = num[1:]
 	} else {
 		num[0] = '+'
 	}
-	// Special handling for infinity, which doesn't look like a number so shouldn't be padded with zeros.
-	if math.IsInf(v, 0) {
-		if f.zero {
-			defer func() { f.zero = true }()
-			f.zero = false
-		}
+	// f.space means to add a leading space instead of a "+" sign unless
+	// the sign is explicitly asked for by f.plus.
+	if f.space && num[0] == '+' && !f.plus {
+		num[0] = ' '
 	}
-	// num is now a signed version of the number.
-	// If we're zero padding, want the sign before the leading zeros.
-	// Achieve this by writing the sign out and then padding the unsigned number.
-	if f.zero && f.widPresent && f.wid > len(num) {
-		if f.space && v >= 0 {
-			f.buf.WriteByte(' ') // This is what C does: even with zero, f.space means space.
-			f.wid--
-		} else if f.plus || v < 0 {
-			f.buf.WriteByte(num[0])
-			f.wid--
+	// Special handling for infinities and NaN,
+	// which don't look like a number so shouldn't be padded with zeros.
+	if num[1] == 'I' || num[1] == 'N' {
+		oldZero := f.zero
+		f.zero = false
+		// Remove sign before NaN if not asked for.
+		if num[1] == 'N' && !f.space && !f.plus {
+			num = num[1:]
 		}
-		f.pad(num[1:])
-		return
-	}
-	// f.space says to replace a leading + with a space.
-	if f.space && num[0] == '+' {
-		num[0] = ' '
 		f.pad(num)
+		f.zero = oldZero
 		return
 	}
-	// Now we know the sign is attached directly to the number, if present at all.
-	// We want a sign if asked for, if it's negative, or if it's infinity (+Inf vs. -Inf).
-	if f.plus || num[0] == '-' || math.IsInf(v, 0) {
+	// We want a sign if asked for and if the sign is not positive.
+	if f.plus || num[0] != '+' {
+		// If we're zero padding to the left we want the sign before the leading zeros.
+		// Achieve this by writing the sign out and then padding the unsigned number.
+		if f.zero && f.widPresent && f.wid > len(num) {
+			f.buf.WriteByte(num[0])
+			f.writePadding(f.wid - len(num))
+			f.buf.Write(num[1:])
+			return
+		}
 		f.pad(num)
 		return
 	}
 	// No sign to show and the number is positive; just print the unsigned number.
 	f.pad(num[1:])
 }
-
-// fmt_e64 formats a float64 in the form -1.23e+12.
-func (f *fmt) fmt_e64(v float64) { f.formatFloat(v, 'e', doPrec(f, 6), 64) }
-
-// fmt_E64 formats a float64 in the form -1.23E+12.
-func (f *fmt) fmt_E64(v float64) { f.formatFloat(v, 'E', doPrec(f, 6), 64) }
-
-// fmt_f64 formats a float64 in the form -1.23.
-func (f *fmt) fmt_f64(v float64) { f.formatFloat(v, 'f', doPrec(f, 6), 64) }
-
-// fmt_g64 formats a float64 in the 'f' or 'e' form according to size.
-func (f *fmt) fmt_g64(v float64) { f.formatFloat(v, 'g', doPrec(f, -1), 64) }
-
-// fmt_G64 formats a float64 in the 'f' or 'E' form according to size.
-func (f *fmt) fmt_G64(v float64) { f.formatFloat(v, 'G', doPrec(f, -1), 64) }
-
-// fmt_fb64 formats a float64 in the form -123p3 (exponent is power of 2).
-func (f *fmt) fmt_fb64(v float64) { f.formatFloat(v, 'b', 0, 64) }
-
-// float32
-// cannot defer to float64 versions
-// because it will get rounding wrong in corner cases.
-
-// fmt_e32 formats a float32 in the form -1.23e+12.
-func (f *fmt) fmt_e32(v float32) { f.formatFloat(float64(v), 'e', doPrec(f, 6), 32) }
-
-// fmt_E32 formats a float32 in the form -1.23E+12.
-func (f *fmt) fmt_E32(v float32) { f.formatFloat(float64(v), 'E', doPrec(f, 6), 32) }
-
-// fmt_f32 formats a float32 in the form -1.23.
-func (f *fmt) fmt_f32(v float32) { f.formatFloat(float64(v), 'f', doPrec(f, 6), 32) }
-
-// fmt_g32 formats a float32 in the 'f' or 'e' form according to size.
-func (f *fmt) fmt_g32(v float32) { f.formatFloat(float64(v), 'g', doPrec(f, -1), 32) }
-
-// fmt_G32 formats a float32 in the 'f' or 'E' form according to size.
-func (f *fmt) fmt_G32(v float32) { f.formatFloat(float64(v), 'G', doPrec(f, -1), 32) }
-
-// fmt_fb32 formats a float32 in the form -123p3 (exponent is power of 2).
-func (f *fmt) fmt_fb32(v float32) { f.formatFloat(float64(v), 'b', 0, 32) }
-
-// fmt_c64 formats a complex64 according to the verb.
-func (f *fmt) fmt_c64(v complex64, verb rune) {
-	f.fmt_complex(float64(real(v)), float64(imag(v)), 32, verb)
-}
-
-// fmt_c128 formats a complex128 according to the verb.
-func (f *fmt) fmt_c128(v complex128, verb rune) {
-	f.fmt_complex(real(v), imag(v), 64, verb)
-}
-
-// fmt_complex formats a complex number as (r+ji).
-func (f *fmt) fmt_complex(r, j float64, size int, verb rune) {
-	f.buf.WriteByte('(')
-	oldPlus := f.plus
-	oldSpace := f.space
-	oldWid := f.wid
-	for i := 0; ; i++ {
-		switch verb {
-		case 'b':
-			f.formatFloat(r, 'b', 0, size)
-		case 'e':
-			f.formatFloat(r, 'e', doPrec(f, 6), size)
-		case 'E':
-			f.formatFloat(r, 'E', doPrec(f, 6), size)
-		case 'f', 'F':
-			f.formatFloat(r, 'f', doPrec(f, 6), size)
-		case 'g':
-			f.formatFloat(r, 'g', doPrec(f, -1), size)
-		case 'G':
-			f.formatFloat(r, 'G', doPrec(f, -1), size)
-		}
-		if i != 0 {
-			break
-		}
-		// Imaginary part always has a sign.
-		f.plus = true
-		f.space = false
-		f.wid = oldWid
-		r = j
-	}
-	f.space = oldSpace
-	f.plus = oldPlus
-	f.wid = oldWid
-	f.buf.Write(irparenBytes)
-}
diff --git a/libgo/go/fmt/print.go b/libgo/go/fmt/print.go
index ebfa13e..f8c7316 100644
--- a/libgo/go/fmt/print.go
+++ b/libgo/go/fmt/print.go
@@ -13,24 +13,23 @@ import (
 	"unicode/utf8"
 )
 
-// Some constants in the form of bytes, to avoid string overhead.
-// Needlessly fastidious, I suppose.
-var (
-	commaSpaceBytes  = []byte(", ")
-	nilAngleBytes    = []byte("<nil>")
-	nilParenBytes    = []byte("(nil)")
-	nilBytes         = []byte("nil")
-	mapBytes         = []byte("map[")
-	percentBangBytes = []byte("%!")
-	missingBytes     = []byte("(MISSING)")
-	badIndexBytes    = []byte("(BADINDEX)")
-	panicBytes       = []byte("(PANIC=")
-	extraBytes       = []byte("%!(EXTRA ")
-	irparenBytes     = []byte("i)")
-	bytesBytes       = []byte("[]byte{")
-	badWidthBytes    = []byte("%!(BADWIDTH)")
-	badPrecBytes     = []byte("%!(BADPREC)")
-	noVerbBytes      = []byte("%!(NOVERB)")
+// Strings for use with buffer.WriteString.
+// This is less overhead than using buffer.Write with byte arrays.
+const (
+	commaSpaceString  = ", "
+	nilAngleString    = "<nil>"
+	nilParenString    = "(nil)"
+	nilString         = "nil"
+	mapString         = "map["
+	percentBangString = "%!"
+	missingString     = "(MISSING)"
+	badIndexString    = "(BADINDEX)"
+	panicString       = "(PANIC="
+	extraString       = "%!(EXTRA "
+	badWidthString    = "%!(BADWIDTH)"
+	badPrecString     = "%!(BADPREC)"
+	noVerbString      = "%!(NOVERB)"
+	invReflectString  = "<invalid reflect.Value>"
 )
 
 // State represents the printer state passed to custom formatters.
@@ -38,7 +37,7 @@ var (
 // the flags and options for the operand's format specifier.
 type State interface {
 	// Write is the function to call to emit formatted output to be printed.
-	Write(b []byte) (ret int, err error)
+	Write(b []byte) (n int, err error)
 	// Width returns the value of the width option and whether it has been set.
 	Width() (wid int, ok bool)
 	// Precision returns the value of the precision option and whether it has been set.
@@ -75,25 +74,22 @@ type GoStringer interface {
 // Use simple []byte instead of bytes.Buffer to avoid large dependency.
 type buffer []byte
 
-func (b *buffer) Write(p []byte) (n int, err error) {
+func (b *buffer) Write(p []byte) {
 	*b = append(*b, p...)
-	return len(p), nil
 }
 
-func (b *buffer) WriteString(s string) (n int, err error) {
+func (b *buffer) WriteString(s string) {
 	*b = append(*b, s...)
-	return len(s), nil
 }
 
-func (b *buffer) WriteByte(c byte) error {
+func (b *buffer) WriteByte(c byte) {
 	*b = append(*b, c)
-	return nil
 }
 
-func (bp *buffer) WriteRune(r rune) error {
+func (bp *buffer) WriteRune(r rune) {
 	if r < utf8.RuneSelf {
 		*bp = append(*bp, byte(r))
-		return nil
+		return
 	}
 
 	b := *bp
@@ -103,25 +99,29 @@ func (bp *buffer) WriteRune(r rune) error {
 	}
 	w := utf8.EncodeRune(b[n:n+utf8.UTFMax], r)
 	*bp = b[:n+w]
-	return nil
 }
 
+// pp is used to store a printer's state and is reused with sync.Pool to avoid allocations.
 type pp struct {
-	n         int
-	panicking bool
-	erroring  bool // printing an error condition
-	buf       buffer
+	buf buffer
+
 	// arg holds the current item, as an interface{}.
 	arg interface{}
-	// value holds the current item, as a reflect.Value, and will be
-	// the zero Value if the item has not been reflected.
+
+	// value is used instead of arg for reflect values.
 	value reflect.Value
+
+	// fmt is used to format basic items such as integers or strings.
+	fmt fmt
+
 	// reordered records whether the format string used argument reordering.
 	reordered bool
 	// goodArgNum records whether the most recent reordering directive was valid.
 	goodArgNum bool
-	runeBuf    [utf8.UTFMax]byte
-	fmt        fmt
+	// panicking is set by catchPanic to avoid infinite panic, recover, panic, ... recursion.
+	panicking bool
+	// erroring is set when printing an error string to guard against calling handleMethods.
+	erroring bool
 }
 
 var ppFree = sync.Pool{
@@ -139,10 +139,6 @@ func newPrinter() *pp {
 
 // free saves used pp structs in ppFree; avoids an allocation per invocation.
 func (p *pp) free() {
-	// Don't hold on to pp structs with large buffers.
-	if cap(p.buf) > 1024 {
-		return
-	}
 	p.buf = p.buf[:0]
 	p.arg = nil
 	p.value = reflect.Value{}
@@ -158,9 +154,9 @@ func (p *pp) Flag(b int) bool {
 	case '-':
 		return p.fmt.minus
 	case '+':
-		return p.fmt.plus
+		return p.fmt.plus || p.fmt.plusV
 	case '#':
-		return p.fmt.sharp
+		return p.fmt.sharp || p.fmt.sharpV
 	case ' ':
 		return p.fmt.space
 	case '0':
@@ -169,14 +165,11 @@ func (p *pp) Flag(b int) bool {
 	return false
 }
 
-func (p *pp) add(c rune) {
-	p.buf.WriteRune(c)
-}
-
 // Implement Write so we can call Fprintf on a pp (through State), for
 // recursive use in custom verbs.
 func (p *pp) Write(b []byte) (ret int, err error) {
-	return p.buf.Write(b)
+	p.buf.Write(b)
+	return len(b), nil
 }
 
 // These routines end in 'f' and take a format string.
@@ -219,7 +212,7 @@ func Errorf(format string, a ...interface{}) error {
 // It returns the number of bytes written and any write error encountered.
 func Fprint(w io.Writer, a ...interface{}) (n int, err error) {
 	p := newPrinter()
-	p.doPrint(a, false, false)
+	p.doPrint(a)
 	n, err = w.Write(p.buf)
 	p.free()
 	return
@@ -236,7 +229,7 @@ func Print(a ...interface{}) (n int, err error) {
 // Spaces are added between operands when neither is a string.
 func Sprint(a ...interface{}) string {
 	p := newPrinter()
-	p.doPrint(a, false, false)
+	p.doPrint(a)
 	s := string(p.buf)
 	p.free()
 	return s
@@ -251,7 +244,7 @@ func Sprint(a ...interface{}) string {
 // It returns the number of bytes written and any write error encountered.
 func Fprintln(w io.Writer, a ...interface{}) (n int, err error) {
 	p := newPrinter()
-	p.doPrint(a, true, true)
+	p.doPrintln(a)
 	n, err = w.Write(p.buf)
 	p.free()
 	return
@@ -268,7 +261,7 @@ func Println(a ...interface{}) (n int, err error) {
 // Spaces are always added between operands and a newline is appended.
 func Sprintln(a ...interface{}) string {
 	p := newPrinter()
-	p.doPrint(a, true, true)
+	p.doPrintln(a)
 	s := string(p.buf)
 	p.free()
 	return s
@@ -309,7 +302,7 @@ func parsenum(s string, start, end int) (num int, isnum bool, newi int) {
 
 func (p *pp) unknownType(v reflect.Value) {
 	if !v.IsValid() {
-		p.buf.Write(nilAngleBytes)
+		p.buf.WriteString(nilAngleString)
 		return
 	}
 	p.buf.WriteByte('?')
@@ -319,23 +312,22 @@ func (p *pp) unknownType(v reflect.Value) {
 
 func (p *pp) badVerb(verb rune) {
 	p.erroring = true
-	p.add('%')
-	p.add('!')
-	p.add(verb)
-	p.add('(')
+	p.buf.WriteString(percentBangString)
+	p.buf.WriteRune(verb)
+	p.buf.WriteByte('(')
 	switch {
 	case p.arg != nil:
 		p.buf.WriteString(reflect.TypeOf(p.arg).String())
-		p.add('=')
-		p.printArg(p.arg, 'v', 0)
+		p.buf.WriteByte('=')
+		p.printArg(p.arg, 'v')
 	case p.value.IsValid():
 		p.buf.WriteString(p.value.Type().String())
-		p.add('=')
+		p.buf.WriteByte('=')
 		p.printValue(p.value, 'v', 0)
 	default:
-		p.buf.Write(nilAngleBytes)
+		p.buf.WriteString(nilAngleString)
 	}
-	p.add(')')
+	p.buf.WriteByte(')')
 	p.erroring = false
 }
 
@@ -348,162 +340,82 @@ func (p *pp) fmtBool(v bool, verb rune) {
 	}
 }
 
-// fmtC formats a rune for the 'c' format.
-func (p *pp) fmtC(c int64) {
-	r := rune(c) // Check for overflow.
-	if int64(r) != c {
-		r = utf8.RuneError
-	}
-	w := utf8.EncodeRune(p.runeBuf[0:utf8.UTFMax], r)
-	p.fmt.pad(p.runeBuf[0:w])
-}
-
-func (p *pp) fmtInt64(v int64, verb rune) {
-	switch verb {
-	case 'b':
-		p.fmt.integer(v, 2, signed, ldigits)
-	case 'c':
-		p.fmtC(v)
-	case 'd', 'v':
-		p.fmt.integer(v, 10, signed, ldigits)
-	case 'o':
-		p.fmt.integer(v, 8, signed, ldigits)
-	case 'q':
-		if 0 <= v && v <= utf8.MaxRune {
-			p.fmt.fmt_qc(v)
-		} else {
-			p.badVerb(verb)
-		}
-	case 'x':
-		p.fmt.integer(v, 16, signed, ldigits)
-	case 'U':
-		p.fmtUnicode(v)
-	case 'X':
-		p.fmt.integer(v, 16, signed, udigits)
-	default:
-		p.badVerb(verb)
-	}
-}
-
 // fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x or
 // not, as requested, by temporarily setting the sharp flag.
 func (p *pp) fmt0x64(v uint64, leading0x bool) {
 	sharp := p.fmt.sharp
 	p.fmt.sharp = leading0x
-	p.fmt.integer(int64(v), 16, unsigned, ldigits)
+	p.fmt.fmt_integer(v, 16, unsigned, ldigits)
 	p.fmt.sharp = sharp
 }
 
-// fmtUnicode formats a uint64 in U+1234 form by
-// temporarily turning on the unicode flag and tweaking the precision.
-func (p *pp) fmtUnicode(v int64) {
-	precPresent := p.fmt.precPresent
-	sharp := p.fmt.sharp
-	p.fmt.sharp = false
-	prec := p.fmt.prec
-	if !precPresent {
-		// If prec is already set, leave it alone; otherwise 4 is minimum.
-		p.fmt.prec = 4
-		p.fmt.precPresent = true
-	}
-	p.fmt.unicode = true // turn on U+
-	p.fmt.uniQuote = sharp
-	p.fmt.integer(int64(v), 16, unsigned, udigits)
-	p.fmt.unicode = false
-	p.fmt.uniQuote = false
-	p.fmt.prec = prec
-	p.fmt.precPresent = precPresent
-	p.fmt.sharp = sharp
-}
-
-func (p *pp) fmtUint64(v uint64, verb rune) {
+// fmtInteger formats a signed or unsigned integer.
+func (p *pp) fmtInteger(v uint64, isSigned bool, verb rune) {
 	switch verb {
-	case 'b':
-		p.fmt.integer(int64(v), 2, unsigned, ldigits)
-	case 'c':
-		p.fmtC(int64(v))
-	case 'd':
-		p.fmt.integer(int64(v), 10, unsigned, ldigits)
 	case 'v':
-		if p.fmt.sharpV {
+		if p.fmt.sharpV && !isSigned {
 			p.fmt0x64(v, true)
 		} else {
-			p.fmt.integer(int64(v), 10, unsigned, ldigits)
+			p.fmt.fmt_integer(v, 10, isSigned, ldigits)
 		}
+	case 'd':
+		p.fmt.fmt_integer(v, 10, isSigned, ldigits)
+	case 'b':
+		p.fmt.fmt_integer(v, 2, isSigned, ldigits)
 	case 'o':
-		p.fmt.integer(int64(v), 8, unsigned, ldigits)
+		p.fmt.fmt_integer(v, 8, isSigned, ldigits)
+	case 'x':
+		p.fmt.fmt_integer(v, 16, isSigned, ldigits)
+	case 'X':
+		p.fmt.fmt_integer(v, 16, isSigned, udigits)
+	case 'c':
+		p.fmt.fmt_c(v)
 	case 'q':
-		if 0 <= v && v <= utf8.MaxRune {
-			p.fmt.fmt_qc(int64(v))
+		if v <= utf8.MaxRune {
+			p.fmt.fmt_qc(v)
 		} else {
 			p.badVerb(verb)
 		}
-	case 'x':
-		p.fmt.integer(int64(v), 16, unsigned, ldigits)
-	case 'X':
-		p.fmt.integer(int64(v), 16, unsigned, udigits)
 	case 'U':
-		p.fmtUnicode(int64(v))
+		p.fmt.fmt_unicode(v)
 	default:
 		p.badVerb(verb)
 	}
 }
 
-func (p *pp) fmtFloat32(v float32, verb rune) {
+// fmtFloat formats a float. The default precision for each verb
+// is specified as last argument in the call to fmt_float.
+func (p *pp) fmtFloat(v float64, size int, verb rune) {
 	switch verb {
-	case 'b':
-		p.fmt.fmt_fb32(v)
-	case 'e':
-		p.fmt.fmt_e32(v)
-	case 'E':
-		p.fmt.fmt_E32(v)
-	case 'f', 'F':
-		p.fmt.fmt_f32(v)
-	case 'g', 'v':
-		p.fmt.fmt_g32(v)
-	case 'G':
-		p.fmt.fmt_G32(v)
-	default:
-		p.badVerb(verb)
-	}
-}
-
-func (p *pp) fmtFloat64(v float64, verb rune) {
-	switch verb {
-	case 'b':
-		p.fmt.fmt_fb64(v)
-	case 'e':
-		p.fmt.fmt_e64(v)
-	case 'E':
-		p.fmt.fmt_E64(v)
-	case 'f', 'F':
-		p.fmt.fmt_f64(v)
-	case 'g', 'v':
-		p.fmt.fmt_g64(v)
-	case 'G':
-		p.fmt.fmt_G64(v)
-	default:
-		p.badVerb(verb)
-	}
-}
-
-func (p *pp) fmtComplex64(v complex64, verb rune) {
-	switch verb {
-	case 'b', 'e', 'E', 'f', 'F', 'g', 'G':
-		p.fmt.fmt_c64(v, verb)
 	case 'v':
-		p.fmt.fmt_c64(v, 'g')
+		p.fmt.fmt_float(v, size, 'g', -1)
+	case 'b', 'g', 'G':
+		p.fmt.fmt_float(v, size, verb, -1)
+	case 'f', 'e', 'E':
+		p.fmt.fmt_float(v, size, verb, 6)
+	case 'F':
+		p.fmt.fmt_float(v, size, 'f', 6)
 	default:
 		p.badVerb(verb)
 	}
 }
 
-func (p *pp) fmtComplex128(v complex128, verb rune) {
+// fmtComplex formats a complex number v with
+// r = real(v) and j = imag(v) as (r+ji) using
+// fmtFloat for r and j formatting.
+func (p *pp) fmtComplex(v complex128, size int, verb rune) {
+	// Make sure any unsupported verbs are found before the
+	// calls to fmtFloat to not generate an incorrect error string.
 	switch verb {
-	case 'b', 'e', 'E', 'f', 'F', 'g', 'G':
-		p.fmt.fmt_c128(v, verb)
-	case 'v':
-		p.fmt.fmt_c128(v, 'g')
+	case 'v', 'b', 'g', 'G', 'f', 'F', 'e', 'E':
+		oldPlus := p.fmt.plus
+		p.buf.WriteByte('(')
+		p.fmtFloat(real(v), size/2, verb)
+		// Imaginary part always has a sign.
+		p.fmt.plus = true
+		p.fmtFloat(imag(v), size/2, verb)
+		p.buf.WriteString("i)")
+		p.fmt.plus = oldPlus
 	default:
 		p.badVerb(verb)
 	}
@@ -530,45 +442,33 @@ func (p *pp) fmtString(v string, verb rune) {
 	}
 }
 
-func (p *pp) fmtBytes(v []byte, verb rune, typ reflect.Type, depth int) {
-	if verb == 'v' || verb == 'd' {
+func (p *pp) fmtBytes(v []byte, verb rune, typeString string) {
+	switch verb {
+	case 'v', 'd':
 		if p.fmt.sharpV {
+			p.buf.WriteString(typeString)
 			if v == nil {
-				if typ == nil {
-					p.buf.WriteString("[]byte(nil)")
-				} else {
-					p.buf.WriteString(typ.String())
-					p.buf.Write(nilParenBytes)
-				}
+				p.buf.WriteString(nilParenString)
 				return
 			}
-			if typ == nil {
-				p.buf.Write(bytesBytes)
-			} else {
-				p.buf.WriteString(typ.String())
-				p.buf.WriteByte('{')
+			p.buf.WriteByte('{')
+			for i, c := range v {
+				if i > 0 {
+					p.buf.WriteString(commaSpaceString)
+				}
+				p.fmt0x64(uint64(c), true)
 			}
+			p.buf.WriteByte('}')
 		} else {
 			p.buf.WriteByte('[')
-		}
-		for i, c := range v {
-			if i > 0 {
-				if p.fmt.sharpV {
-					p.buf.Write(commaSpaceBytes)
-				} else {
+			for i, c := range v {
+				if i > 0 {
 					p.buf.WriteByte(' ')
 				}
+				p.fmt.fmt_integer(uint64(c), 10, unsigned, ldigits)
 			}
-			p.printArg(c, 'v', depth+1)
-		}
-		if p.fmt.sharpV {
-			p.buf.WriteByte('}')
-		} else {
 			p.buf.WriteByte(']')
 		}
-		return
-	}
-	switch verb {
 	case 's':
 		p.fmt.fmt_s(string(v))
 	case 'x':
@@ -578,23 +478,11 @@ func (p *pp) fmtBytes(v []byte, verb rune, typ reflect.Type, depth int) {
 	case 'q':
 		p.fmt.fmt_q(string(v))
 	default:
-		p.badVerb(verb)
+		p.printValue(reflect.ValueOf(v), verb, 0)
 	}
 }
 
 func (p *pp) fmtPointer(value reflect.Value, verb rune) {
-	use0x64 := true
-	switch verb {
-	case 'p', 'v':
-		// ok
-	case 'b', 'd', 'o', 'x', 'X':
-		use0x64 = false
-		// ok
-	default:
-		p.badVerb(verb)
-		return
-	}
-
 	var u uintptr
 	switch value.Kind() {
 	case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
@@ -604,40 +492,41 @@ func (p *pp) fmtPointer(value reflect.Value, verb rune) {
 		return
 	}
 
-	if p.fmt.sharpV {
-		p.add('(')
-		p.buf.WriteString(value.Type().String())
-		p.add(')')
-		p.add('(')
-		if u == 0 {
-			p.buf.Write(nilBytes)
-		} else {
-			p.fmt0x64(uint64(u), true)
-		}
-		p.add(')')
-	} else if verb == 'v' && u == 0 {
-		p.buf.Write(nilAngleBytes)
-	} else {
-		if use0x64 {
-			p.fmt0x64(uint64(u), !p.fmt.sharp)
+	switch verb {
+	case 'v':
+		if p.fmt.sharpV {
+			p.buf.WriteByte('(')
+			p.buf.WriteString(value.Type().String())
+			p.buf.WriteString(")(")
+			if u == 0 {
+				p.buf.WriteString(nilString)
+			} else {
+				p.fmt0x64(uint64(u), true)
+			}
+			p.buf.WriteByte(')')
 		} else {
-			p.fmtUint64(uint64(u), verb)
+			if u == 0 {
+				p.fmt.padString(nilAngleString)
+			} else {
+				p.fmt0x64(uint64(u), !p.fmt.sharp)
+			}
 		}
+	case 'p':
+		p.fmt0x64(uint64(u), !p.fmt.sharp)
+	case 'b', 'o', 'd', 'x', 'X':
+		p.fmtInteger(uint64(u), unsigned, verb)
+	default:
+		p.badVerb(verb)
 	}
 }
 
-var (
-	intBits     = reflect.TypeOf(0).Bits()
-	uintptrBits = reflect.TypeOf(uintptr(0)).Bits()
-)
-
 func (p *pp) catchPanic(arg interface{}, verb rune) {
 	if err := recover(); err != nil {
 		// If it's a nil pointer, just say "<nil>". The likeliest causes are a
 		// Stringer that fails to guard against nil or a nil pointer for a
 		// value receiver, and in either case, "<nil>" is a nice result.
 		if v := reflect.ValueOf(arg); v.Kind() == reflect.Ptr && v.IsNil() {
-			p.buf.Write(nilAngleBytes)
+			p.buf.WriteString(nilAngleString)
 			return
 		}
 		// Otherwise print a concise panic message. Most of the time the panic
@@ -647,52 +536,23 @@ func (p *pp) catchPanic(arg interface{}, verb rune) {
 			panic(err)
 		}
 		p.fmt.clearflags() // We are done, and for this output we want default behavior.
-		p.buf.Write(percentBangBytes)
-		p.add(verb)
-		p.buf.Write(panicBytes)
+		p.buf.WriteString(percentBangString)
+		p.buf.WriteRune(verb)
+		p.buf.WriteString(panicString)
 		p.panicking = true
-		p.printArg(err, 'v', 0)
+		p.printArg(err, 'v')
 		p.panicking = false
 		p.buf.WriteByte(')')
 	}
 }
 
-// clearSpecialFlags pushes %#v back into the regular flags and returns their old state.
-func (p *pp) clearSpecialFlags() (plusV, sharpV bool) {
-	plusV = p.fmt.plusV
-	if plusV {
-		p.fmt.plus = true
-		p.fmt.plusV = false
-	}
-	sharpV = p.fmt.sharpV
-	if sharpV {
-		p.fmt.sharp = true
-		p.fmt.sharpV = false
-	}
-	return
-}
-
-// restoreSpecialFlags, whose argument should be a call to clearSpecialFlags,
-// restores the setting of the plusV and sharpV flags.
-func (p *pp) restoreSpecialFlags(plusV, sharpV bool) {
-	if plusV {
-		p.fmt.plus = false
-		p.fmt.plusV = true
-	}
-	if sharpV {
-		p.fmt.sharp = false
-		p.fmt.sharpV = true
-	}
-}
-
-func (p *pp) handleMethods(verb rune, depth int) (handled bool) {
+func (p *pp) handleMethods(verb rune) (handled bool) {
 	if p.erroring {
 		return
 	}
 	// Is it a Formatter?
 	if formatter, ok := p.arg.(Formatter); ok {
 		handled = true
-		defer p.restoreSpecialFlags(p.clearSpecialFlags())
 		defer p.catchPanic(p.arg, verb)
 		formatter.Format(p, verb)
 		return
@@ -721,13 +581,13 @@ func (p *pp) handleMethods(verb rune, depth int) (handled bool) {
 			case error:
 				handled = true
 				defer p.catchPanic(p.arg, verb)
-				p.printArg(v.Error(), verb, depth)
+				p.fmtString(v.Error(), verb)
 				return
 
 			case Stringer:
 				handled = true
 				defer p.catchPanic(p.arg, verb)
-				p.printArg(v.String(), verb, depth)
+				p.fmtString(v.String(), verb)
 				return
 			}
 		}
@@ -735,28 +595,29 @@ func (p *pp) handleMethods(verb rune, depth int) (handled bool) {
 	return false
 }
 
-func (p *pp) printArg(arg interface{}, verb rune, depth int) (wasString bool) {
+func (p *pp) printArg(arg interface{}, verb rune) {
 	p.arg = arg
 	p.value = reflect.Value{}
 
 	if arg == nil {
-		if verb == 'T' || verb == 'v' {
-			p.fmt.pad(nilAngleBytes)
-		} else {
+		switch verb {
+		case 'T', 'v':
+			p.fmt.padString(nilAngleString)
+		default:
 			p.badVerb(verb)
 		}
-		return false
+		return
 	}
 
 	// Special processing considerations.
 	// %T (the value's type) and %p (its address) are special; we always do them first.
 	switch verb {
 	case 'T':
-		p.printArg(reflect.TypeOf(arg).String(), 's', 0)
-		return false
+		p.fmt.fmt_s(reflect.TypeOf(arg).String())
+		return
 	case 'p':
-		p.fmtPointer(reflect.ValueOf(arg), verb)
-		return false
+		p.fmtPointer(reflect.ValueOf(arg), 'p')
+		return
 	}
 
 	// Some types can be done without reflection.
@@ -764,137 +625,110 @@ func (p *pp) printArg(arg interface{}, verb rune, depth int) (wasString bool) {
 	case bool:
 		p.fmtBool(f, verb)
 	case float32:
-		p.fmtFloat32(f, verb)
+		p.fmtFloat(float64(f), 32, verb)
 	case float64:
-		p.fmtFloat64(f, verb)
+		p.fmtFloat(f, 64, verb)
 	case complex64:
-		p.fmtComplex64(f, verb)
+		p.fmtComplex(complex128(f), 64, verb)
 	case complex128:
-		p.fmtComplex128(f, verb)
+		p.fmtComplex(f, 128, verb)
 	case int:
-		p.fmtInt64(int64(f), verb)
+		p.fmtInteger(uint64(f), signed, verb)
 	case int8:
-		p.fmtInt64(int64(f), verb)
+		p.fmtInteger(uint64(f), signed, verb)
 	case int16:
-		p.fmtInt64(int64(f), verb)
+		p.fmtInteger(uint64(f), signed, verb)
 	case int32:
-		p.fmtInt64(int64(f), verb)
+		p.fmtInteger(uint64(f), signed, verb)
 	case int64:
-		p.fmtInt64(f, verb)
+		p.fmtInteger(uint64(f), signed, verb)
 	case uint:
-		p.fmtUint64(uint64(f), verb)
+		p.fmtInteger(uint64(f), unsigned, verb)
 	case uint8:
-		p.fmtUint64(uint64(f), verb)
+		p.fmtInteger(uint64(f), unsigned, verb)
 	case uint16:
-		p.fmtUint64(uint64(f), verb)
+		p.fmtInteger(uint64(f), unsigned, verb)
 	case uint32:
-		p.fmtUint64(uint64(f), verb)
+		p.fmtInteger(uint64(f), unsigned, verb)
 	case uint64:
-		p.fmtUint64(f, verb)
+		p.fmtInteger(f, unsigned, verb)
 	case uintptr:
-		p.fmtUint64(uint64(f), verb)
+		p.fmtInteger(uint64(f), unsigned, verb)
 	case string:
 		p.fmtString(f, verb)
-		wasString = verb == 's' || verb == 'v'
 	case []byte:
-		p.fmtBytes(f, verb, nil, depth)
-		wasString = verb == 's'
+		p.fmtBytes(f, verb, "[]byte")
 	case reflect.Value:
-		return p.printReflectValue(f, verb, depth)
+		p.printValue(f, verb, 0)
 	default:
 		// If the type is not simple, it might have methods.
-		if handled := p.handleMethods(verb, depth); handled {
-			return false
+		if !p.handleMethods(verb) {
+			// Need to use reflection, since the type had no
+			// interface methods that could be used for formatting.
+			p.printValue(reflect.ValueOf(f), verb, 0)
 		}
-		// Need to use reflection
-		return p.printReflectValue(reflect.ValueOf(arg), verb, depth)
 	}
-	p.arg = nil
-	return
 }
 
-// printValue is like printArg but starts with a reflect value, not an interface{} value.
-func (p *pp) printValue(value reflect.Value, verb rune, depth int) (wasString bool) {
-	if !value.IsValid() {
-		if verb == 'T' || verb == 'v' {
-			p.buf.Write(nilAngleBytes)
-		} else {
-			p.badVerb(verb)
-		}
-		return false
-	}
-
-	// Special processing considerations.
-	// %T (the value's type) and %p (its address) are special; we always do them first.
-	switch verb {
-	case 'T':
-		p.printArg(value.Type().String(), 's', 0)
-		return false
-	case 'p':
-		p.fmtPointer(value, verb)
-		return false
-	}
+var byteType = reflect.TypeOf(byte(0))
 
-	// Handle values with special methods.
-	// Call always, even when arg == nil, because handleMethods clears p.fmt.plus for us.
-	p.arg = nil // Make sure it's cleared, for safety.
-	if value.CanInterface() {
+// printValue is similar to printArg but starts with a reflect value, not an interface{} value.
+// It does not handle 'p' and 'T' verbs because these should have been already handled by printArg.
+func (p *pp) printValue(value reflect.Value, verb rune, depth int) {
+	// Handle values with special methods if not already handled by printArg (depth == 0).
+	if depth > 0 && value.IsValid() && value.CanInterface() {
 		p.arg = value.Interface()
+		if p.handleMethods(verb) {
+			return
+		}
 	}
-	if handled := p.handleMethods(verb, depth); handled {
-		return false
-	}
-
-	return p.printReflectValue(value, verb, depth)
-}
-
-var byteType = reflect.TypeOf(byte(0))
-
-// printReflectValue is the fallback for both printArg and printValue.
-// It uses reflect to print the value.
-func (p *pp) printReflectValue(value reflect.Value, verb rune, depth int) (wasString bool) {
-	oldValue := p.value
+	p.arg = nil
 	p.value = value
-BigSwitch:
-	switch f := value; f.Kind() {
+
+	switch f := value; value.Kind() {
 	case reflect.Invalid:
-		p.buf.WriteString("<invalid reflect.Value>")
+		if depth == 0 {
+			p.buf.WriteString(invReflectString)
+		} else {
+			switch verb {
+			case 'v':
+				p.buf.WriteString(nilAngleString)
+			default:
+				p.badVerb(verb)
+			}
+		}
 	case reflect.Bool:
 		p.fmtBool(f.Bool(), verb)
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		p.fmtInt64(f.Int(), verb)
+		p.fmtInteger(uint64(f.Int()), signed, verb)
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		p.fmtUint64(f.Uint(), verb)
-	case reflect.Float32, reflect.Float64:
-		if f.Type().Size() == 4 {
-			p.fmtFloat32(float32(f.Float()), verb)
-		} else {
-			p.fmtFloat64(f.Float(), verb)
-		}
-	case reflect.Complex64, reflect.Complex128:
-		if f.Type().Size() == 8 {
-			p.fmtComplex64(complex64(f.Complex()), verb)
-		} else {
-			p.fmtComplex128(f.Complex(), verb)
-		}
+		p.fmtInteger(f.Uint(), unsigned, verb)
+	case reflect.Float32:
+		p.fmtFloat(f.Float(), 32, verb)
+	case reflect.Float64:
+		p.fmtFloat(f.Float(), 64, verb)
+	case reflect.Complex64:
+		p.fmtComplex(f.Complex(), 64, verb)
+	case reflect.Complex128:
+		p.fmtComplex(f.Complex(), 128, verb)
 	case reflect.String:
 		p.fmtString(f.String(), verb)
 	case reflect.Map:
 		if p.fmt.sharpV {
 			p.buf.WriteString(f.Type().String())
 			if f.IsNil() {
-				p.buf.WriteString("(nil)")
-				break
+				p.buf.WriteString(nilParenString)
+				return
 			}
 			p.buf.WriteByte('{')
 		} else {
-			p.buf.Write(mapBytes)
+			p.buf.WriteString(mapString)
 		}
 		keys := f.MapKeys()
 		for i, key := range keys {
 			if i > 0 {
 				if p.fmt.sharpV {
-					p.buf.Write(commaSpaceBytes)
+					p.buf.WriteString(commaSpaceString)
 				} else {
 					p.buf.WriteByte(' ')
 				}
@@ -910,26 +744,24 @@ BigSwitch:
 		}
 	case reflect.Struct:
 		if p.fmt.sharpV {
-			p.buf.WriteString(value.Type().String())
+			p.buf.WriteString(f.Type().String())
 		}
-		p.add('{')
-		v := f
-		t := v.Type()
-		for i := 0; i < v.NumField(); i++ {
+		p.buf.WriteByte('{')
+		for i := 0; i < f.NumField(); i++ {
 			if i > 0 {
 				if p.fmt.sharpV {
-					p.buf.Write(commaSpaceBytes)
+					p.buf.WriteString(commaSpaceString)
 				} else {
 					p.buf.WriteByte(' ')
 				}
 			}
 			if p.fmt.plusV || p.fmt.sharpV {
-				if f := t.Field(i); f.Name != "" {
-					p.buf.WriteString(f.Name)
+				if name := f.Type().Field(i).Name; name != "" {
+					p.buf.WriteString(name)
 					p.buf.WriteByte(':')
 				}
 			}
-			p.printValue(getField(v, i), verb, depth+1)
+			p.printValue(getField(f, i), verb, depth+1)
 		}
 		p.buf.WriteByte('}')
 	case reflect.Interface:
@@ -937,91 +769,79 @@ BigSwitch:
 		if !value.IsValid() {
 			if p.fmt.sharpV {
 				p.buf.WriteString(f.Type().String())
-				p.buf.Write(nilParenBytes)
+				p.buf.WriteString(nilParenString)
 			} else {
-				p.buf.Write(nilAngleBytes)
+				p.buf.WriteString(nilAngleString)
 			}
 		} else {
-			wasString = p.printValue(value, verb, depth+1)
+			p.printValue(value, verb, depth+1)
 		}
 	case reflect.Array, reflect.Slice:
-		// Byte slices are special:
-		// - Handle []byte (== []uint8) with fmtBytes.
-		// - Handle []T, where T is a named byte type, with fmtBytes only
-		//   for the s, q, an x verbs. For other verbs, T might be a
-		//   Stringer, so we use printValue to print each element.
-		if typ := f.Type(); typ.Elem().Kind() == reflect.Uint8 && (typ.Elem() == byteType || verb == 's' || verb == 'q' || verb == 'x') {
-			var bytes []byte
-			if f.Kind() == reflect.Slice {
-				bytes = f.Bytes()
-			} else if f.CanAddr() {
-				bytes = f.Slice(0, f.Len()).Bytes()
-			} else {
-				// We have an array, but we cannot Slice() a non-addressable array,
-				// so we build a slice by hand. This is a rare case but it would be nice
-				// if reflection could help a little more.
-				bytes = make([]byte, f.Len())
-				for i := range bytes {
-					bytes[i] = byte(f.Index(i).Uint())
+		switch verb {
+		case 's', 'q', 'x', 'X':
+			// Handle byte and uint8 slices and arrays special for the above verbs.
+			t := f.Type()
+			if t.Elem().Kind() == reflect.Uint8 {
+				var bytes []byte
+				if f.Kind() == reflect.Slice {
+					bytes = f.Bytes()
+				} else if f.CanAddr() {
+					bytes = f.Slice(0, f.Len()).Bytes()
+				} else {
+					// We have an array, but we cannot Slice() a non-addressable array,
+					// so we build a slice by hand. This is a rare case but it would be nice
+					// if reflection could help a little more.
+					bytes = make([]byte, f.Len())
+					for i := range bytes {
+						bytes[i] = byte(f.Index(i).Uint())
+					}
 				}
+				p.fmtBytes(bytes, verb, t.String())
+				return
 			}
-			p.fmtBytes(bytes, verb, typ, depth)
-			wasString = verb == 's'
-			break
 		}
 		if p.fmt.sharpV {
-			p.buf.WriteString(value.Type().String())
+			p.buf.WriteString(f.Type().String())
 			if f.Kind() == reflect.Slice && f.IsNil() {
-				p.buf.WriteString("(nil)")
-				break
+				p.buf.WriteString(nilParenString)
+				return
+			} else {
+				p.buf.WriteByte('{')
+				for i := 0; i < f.Len(); i++ {
+					if i > 0 {
+						p.buf.WriteString(commaSpaceString)
+					}
+					p.printValue(f.Index(i), verb, depth+1)
+				}
+				p.buf.WriteByte('}')
 			}
-			p.buf.WriteByte('{')
 		} else {
 			p.buf.WriteByte('[')
-		}
-		for i := 0; i < f.Len(); i++ {
-			if i > 0 {
-				if p.fmt.sharpV {
-					p.buf.Write(commaSpaceBytes)
-				} else {
+			for i := 0; i < f.Len(); i++ {
+				if i > 0 {
 					p.buf.WriteByte(' ')
 				}
+				p.printValue(f.Index(i), verb, depth+1)
 			}
-			p.printValue(f.Index(i), verb, depth+1)
-		}
-		if p.fmt.sharpV {
-			p.buf.WriteByte('}')
-		} else {
 			p.buf.WriteByte(']')
 		}
 	case reflect.Ptr:
-		v := f.Pointer()
 		// pointer to array or slice or struct?  ok at top level
 		// but not embedded (avoid loops)
-		if v != 0 && depth == 0 {
+		if depth == 0 && f.Pointer() != 0 {
 			switch a := f.Elem(); a.Kind() {
-			case reflect.Array, reflect.Slice:
-				p.buf.WriteByte('&')
-				p.printValue(a, verb, depth+1)
-				break BigSwitch
-			case reflect.Struct:
-				p.buf.WriteByte('&')
-				p.printValue(a, verb, depth+1)
-				break BigSwitch
-			case reflect.Map:
+			case reflect.Array, reflect.Slice, reflect.Struct, reflect.Map:
 				p.buf.WriteByte('&')
 				p.printValue(a, verb, depth+1)
-				break BigSwitch
+				return
 			}
 		}
 		fallthrough
 	case reflect.Chan, reflect.Func, reflect.UnsafePointer:
-		p.fmtPointer(value, verb)
+		p.fmtPointer(f, verb)
 	default:
 		p.unknownType(f)
 	}
-	p.value = oldValue
-	return wasString
 }
 
 // intFromArg gets the argNumth element of a. On return, isInt reports whether the argument has integer type.
@@ -1098,11 +918,24 @@ func (p *pp) argNumber(argNum int, format string, i int, numArgs int) (newArgNum
 	return argNum, i + wid, ok
 }
 
+func (p *pp) badArgNum(verb rune) {
+	p.buf.WriteString(percentBangString)
+	p.buf.WriteRune(verb)
+	p.buf.WriteString(badIndexString)
+}
+
+func (p *pp) missingArg(verb rune) {
+	p.buf.WriteString(percentBangString)
+	p.buf.WriteRune(verb)
+	p.buf.WriteString(missingString)
+}
+
 func (p *pp) doPrintf(format string, a []interface{}) {
 	end := len(format)
 	argNum := 0         // we process one argument per non-trivial format
 	afterIndex := false // previous item in format was an index like [3].
 	p.reordered = false
+formatLoop:
 	for i := 0; i < end; {
 		p.goodArgNum = true
 		lasti := i
@@ -1122,21 +955,40 @@ func (p *pp) doPrintf(format string, a []interface{}) {
 
 		// Do we have flags?
 		p.fmt.clearflags()
-	F:
+	simpleFormat:
 		for ; i < end; i++ {
-			switch format[i] {
+			c := format[i]
+			switch c {
 			case '#':
 				p.fmt.sharp = true
 			case '0':
-				p.fmt.zero = true
+				p.fmt.zero = !p.fmt.minus // Only allow zero padding to the left.
 			case '+':
 				p.fmt.plus = true
 			case '-':
 				p.fmt.minus = true
+				p.fmt.zero = false // Do not pad with zeros to the right.
 			case ' ':
 				p.fmt.space = true
 			default:
-				break F
+				// Fast path for common case of ascii lower case simple verbs
+				// without precision or width or argument indices.
+				if 'a' <= c && c <= 'z' && argNum < len(a) {
+					if c == 'v' {
+						// Go syntax
+						p.fmt.sharpV = p.fmt.sharp
+						p.fmt.sharp = false
+						// Struct-field syntax
+						p.fmt.plusV = p.fmt.plus
+						p.fmt.plus = false
+					}
+					p.printArg(a[argNum], rune(c))
+					argNum++
+					i++
+					continue formatLoop
+				}
+				// Format is more complex than simple flags and a verb or is malformed.
+				break simpleFormat
 			}
 		}
 
@@ -1149,7 +1001,7 @@ func (p *pp) doPrintf(format string, a []interface{}) {
 			p.fmt.wid, p.fmt.widPresent, argNum = intFromArg(a, argNum)
 
 			if !p.fmt.widPresent {
-				p.buf.Write(badWidthBytes)
+				p.buf.WriteString(badWidthString)
 			}
 
 			// We have a negative width, so take its value and ensure
@@ -1157,6 +1009,7 @@ func (p *pp) doPrintf(format string, a []interface{}) {
 			if p.fmt.wid < 0 {
 				p.fmt.wid = -p.fmt.wid
 				p.fmt.minus = true
+				p.fmt.zero = false // Do not pad with zeros to the right.
 			}
 			afterIndex = false
 		} else {
@@ -1182,7 +1035,7 @@ func (p *pp) doPrintf(format string, a []interface{}) {
 					p.fmt.precPresent = false
 				}
 				if !p.fmt.precPresent {
-					p.buf.Write(badPrecBytes)
+					p.buf.WriteString(badPrecString)
 				}
 				afterIndex = false
 			} else {
@@ -1199,80 +1052,77 @@ func (p *pp) doPrintf(format string, a []interface{}) {
 		}
 
 		if i >= end {
-			p.buf.Write(noVerbBytes)
-			continue
+			p.buf.WriteString(noVerbString)
+			break
 		}
-		c, w := utf8.DecodeRuneInString(format[i:])
+
+		verb, w := utf8.DecodeRuneInString(format[i:])
 		i += w
-		// percent is special - absorbs no operand
-		if c == '%' {
-			p.buf.WriteByte('%') // We ignore width and prec.
-			continue
-		}
-		if !p.goodArgNum {
-			p.buf.Write(percentBangBytes)
-			p.add(c)
-			p.buf.Write(badIndexBytes)
-			continue
-		} else if argNum >= len(a) { // out of operands
-			p.buf.Write(percentBangBytes)
-			p.add(c)
-			p.buf.Write(missingBytes)
-			continue
-		}
-		arg := a[argNum]
-		argNum++
-
-		if c == 'v' {
-			if p.fmt.sharp {
-				// Go syntax. Set the flag in the fmt and clear the sharp flag.
-				p.fmt.sharp = false
-				p.fmt.sharpV = true
-			}
-			if p.fmt.plus {
-				// Struct-field syntax. Set the flag in the fmt and clear the plus flag.
-				p.fmt.plus = false
-				p.fmt.plusV = true
-			}
+
+		switch {
+		case verb == '%': // Percent does not absorb operands and ignores f.wid and f.prec.
+			p.buf.WriteByte('%')
+		case !p.goodArgNum:
+			p.badArgNum(verb)
+		case argNum >= len(a): // No argument left over to print for the current verb.
+			p.missingArg(verb)
+		case verb == 'v':
+			// Go syntax
+			p.fmt.sharpV = p.fmt.sharp
+			p.fmt.sharp = false
+			// Struct-field syntax
+			p.fmt.plusV = p.fmt.plus
+			p.fmt.plus = false
+			fallthrough
+		default:
+			p.printArg(a[argNum], verb)
+			argNum++
 		}
-		p.printArg(arg, c, 0)
 	}
 
 	// Check for extra arguments unless the call accessed the arguments
 	// out of order, in which case it's too expensive to detect if they've all
 	// been used and arguably OK if they're not.
 	if !p.reordered && argNum < len(a) {
-		p.buf.Write(extraBytes)
-		for ; argNum < len(a); argNum++ {
-			arg := a[argNum]
-			if arg != nil {
+		p.fmt.clearflags()
+		p.buf.WriteString(extraString)
+		for i, arg := range a[argNum:] {
+			if i > 0 {
+				p.buf.WriteString(commaSpaceString)
+			}
+			if arg == nil {
+				p.buf.WriteString(nilAngleString)
+			} else {
 				p.buf.WriteString(reflect.TypeOf(arg).String())
 				p.buf.WriteByte('=')
-			}
-			p.printArg(arg, 'v', 0)
-			if argNum+1 < len(a) {
-				p.buf.Write(commaSpaceBytes)
+				p.printArg(arg, 'v')
 			}
 		}
 		p.buf.WriteByte(')')
 	}
 }
 
-func (p *pp) doPrint(a []interface{}, addspace, addnewline bool) {
+func (p *pp) doPrint(a []interface{}) {
 	prevString := false
-	for argNum := 0; argNum < len(a); argNum++ {
-		p.fmt.clearflags()
-		// always add spaces if we're doing Println
-		arg := a[argNum]
-		if argNum > 0 {
-			isString := arg != nil && reflect.TypeOf(arg).Kind() == reflect.String
-			if addspace || !isString && !prevString {
-				p.buf.WriteByte(' ')
-			}
+	for argNum, arg := range a {
+		isString := arg != nil && reflect.TypeOf(arg).Kind() == reflect.String
+		// Add a space between two non-string arguments.
+		if argNum > 0 && !isString && !prevString {
+			p.buf.WriteByte(' ')
 		}
-		prevString = p.printArg(arg, 'v', 0)
+		p.printArg(arg, 'v')
+		prevString = isString
 	}
-	if addnewline {
-		p.buf.WriteByte('\n')
+}
+
+// doPrintln is like doPrint but always adds a space between arguments
+// and a newline after the last argument.
+func (p *pp) doPrintln(a []interface{}) {
+	for argNum, arg := range a {
+		if argNum > 0 {
+			p.buf.WriteByte(' ')
+		}
+		p.printArg(arg, 'v')
 	}
+	p.buf.WriteByte('\n')
 }
diff --git a/libgo/go/fmt/scan.go b/libgo/go/fmt/scan.go
index 4618ed4..fdf4197 100644
--- a/libgo/go/fmt/scan.go
+++ b/libgo/go/fmt/scan.go
@@ -15,14 +15,6 @@ import (
 	"unicode/utf8"
 )
 
-// runeUnreader is the interface to something that can unread runes.
-// If the object provided to Scan does not satisfy this interface,
-// a local buffer will be used to back up the input, but its contents
-// will be lost when Scan returns.
-type runeUnreader interface {
-	UnreadRune() error
-}
-
 // ScanState represents the scanner state passed to custom scanners.
 // Scanners may do rune-at-a-time scanning or ask the ScanState
 // to discover the next space-delimited token.
@@ -41,7 +33,7 @@ type ScanState interface {
 	// Token skips space in the input if skipSpace is true, then returns the
 	// run of Unicode code points c satisfying f(c).  If f is nil,
 	// !unicode.IsSpace(c) is used; that is, the token will hold non-space
-	// characters.  Newlines are treated appropriately for the operation being
+	// characters. Newlines are treated appropriately for the operation being
 	// performed; see the package documentation for more information.
 	// The returned slice points to shared data that may be overwritten
 	// by the next call to Token, a call to a Scan function using the ScanState
@@ -58,15 +50,15 @@ type ScanState interface {
 
 // Scanner is implemented by any value that has a Scan method, which scans
 // the input for the representation of a value and stores the result in the
-// receiver, which must be a pointer to be useful.  The Scan method is called
+// receiver, which must be a pointer to be useful. The Scan method is called
 // for any argument to Scan, Scanf, or Scanln that implements it.
 type Scanner interface {
 	Scan(state ScanState, verb rune) error
 }
 
 // Scan scans text read from standard input, storing successive
-// space-separated values into successive arguments.  Newlines count
-// as space.  It returns the number of items successfully scanned.
+// space-separated values into successive arguments. Newlines count
+// as space. It returns the number of items successfully scanned.
 // If that is less than the number of arguments, err will report why.
 func Scan(a ...interface{}) (n int, err error) {
 	return Fscan(os.Stdin, a...)
@@ -80,7 +72,7 @@ func Scanln(a ...interface{}) (n int, err error) {
 
 // Scanf scans text read from standard input, storing successive
 // space-separated values into successive arguments as determined by
-// the format.  It returns the number of items successfully scanned.
+// the format. It returns the number of items successfully scanned.
 // If that is less than the number of arguments, err will report why.
 // Newlines in the input must match newlines in the format.
 // The one exception: the verb %c always scans the next rune in the
@@ -101,8 +93,8 @@ func (r *stringReader) Read(b []byte) (n int, err error) {
 }
 
 // Sscan scans the argument string, storing successive space-separated
-// values into successive arguments.  Newlines count as space.  It
-// returns the number of items successfully scanned.  If that is less
+// values into successive arguments. Newlines count as space. It
+// returns the number of items successfully scanned. If that is less
 // than the number of arguments, err will report why.
 func Sscan(str string, a ...interface{}) (n int, err error) {
 	return Fscan((*stringReader)(&str), a...)
@@ -115,7 +107,7 @@ func Sscanln(str string, a ...interface{}) (n int, err error) {
 }
 
 // Sscanf scans the argument string, storing successive space-separated
-// values into successive arguments as determined by the format.  It
+// values into successive arguments as determined by the format. It
 // returns the number of items successfully parsed.
 // Newlines in the input must match newlines in the format.
 func Sscanf(str string, format string, a ...interface{}) (n int, err error) {
@@ -123,8 +115,8 @@ func Sscanf(str string, format string, a ...interface{}) (n int, err error) {
 }
 
 // Fscan scans text read from r, storing successive space-separated
-// values into successive arguments.  Newlines count as space.  It
-// returns the number of items successfully scanned.  If that is less
+// values into successive arguments. Newlines count as space. It
+// returns the number of items successfully scanned. If that is less
 // than the number of arguments, err will report why.
 func Fscan(r io.Reader, a ...interface{}) (n int, err error) {
 	s, old := newScanState(r, true, false)
@@ -143,7 +135,7 @@ func Fscanln(r io.Reader, a ...interface{}) (n int, err error) {
 }
 
 // Fscanf scans text read from r, storing successive space-separated
-// values into successive arguments as determined by the format.  It
+// values into successive arguments as determined by the format. It
 // returns the number of items successfully parsed.
 // Newlines in the input must match newlines in the format.
 func Fscanf(r io.Reader, format string, a ...interface{}) (n int, err error) {
@@ -163,12 +155,10 @@ const eof = -1
 
 // ss is the internal implementation of ScanState.
 type ss struct {
-	rr       io.RuneReader // where to read input
-	buf      buffer        // token accumulator
-	peekRune rune          // one-rune lookahead
-	prevRune rune          // last rune returned by ReadRune
-	count    int           // runes consumed so far.
-	atEOF    bool          // already read EOF
+	rs    io.RuneScanner // where to read input
+	buf   buffer         // token accumulator
+	count int            // runes consumed so far.
+	atEOF bool           // already read EOF
 	ssave
 }
 
@@ -191,23 +181,17 @@ func (s *ss) Read(buf []byte) (n int, err error) {
 }
 
 func (s *ss) ReadRune() (r rune, size int, err error) {
-	if s.peekRune >= 0 {
-		s.count++
-		r = s.peekRune
-		size = utf8.RuneLen(r)
-		s.prevRune = r
-		s.peekRune = -1
-		return
-	}
-	if s.atEOF || s.nlIsEnd && s.prevRune == '\n' || s.count >= s.argLimit {
+	if s.atEOF || s.count >= s.argLimit {
 		err = io.EOF
 		return
 	}
 
-	r, size, err = s.rr.ReadRune()
+	r, size, err = s.rs.ReadRune()
 	if err == nil {
 		s.count++
-		s.prevRune = r
+		if s.nlIsEnd && r == '\n' {
+			s.atEOF = true
+		}
 	} else if err == io.EOF {
 		s.atEOF = true
 	}
@@ -246,12 +230,8 @@ func (s *ss) mustReadRune() (r rune) {
 }
 
 func (s *ss) UnreadRune() error {
-	if u, ok := s.rr.(runeUnreader); ok {
-		u.UnreadRune()
-	} else {
-		s.peekRune = s.prevRune
-	}
-	s.prevRune = -1
+	s.rs.UnreadRune()
+	s.atEOF = false
 	s.count--
 	return nil
 }
@@ -326,13 +306,14 @@ func (s *ss) SkipSpace() {
 }
 
 // readRune is a structure to enable reading UTF-8 encoded code points
-// from an io.Reader.  It is used if the Reader given to the scanner does
-// not already implement io.RuneReader.
+// from an io.Reader. It is used if the Reader given to the scanner does
+// not already implement io.RuneScanner.
 type readRune struct {
-	reader  io.Reader
-	buf     [utf8.UTFMax]byte // used only inside ReadRune
-	pending int               // number of bytes in pendBuf; only >0 for bad UTF-8
-	pendBuf [utf8.UTFMax]byte // bytes left over
+	reader   io.Reader
+	buf      [utf8.UTFMax]byte // used only inside ReadRune
+	pending  int               // number of bytes in pendBuf; only >0 for bad UTF-8
+	pendBuf  [utf8.UTFMax]byte // bytes left over
+	peekRune rune              // if >=0 next rune; when <0 is ^(previous Rune)
 }
 
 // readByte returns the next byte from the input, which may be
@@ -344,33 +325,35 @@ func (r *readRune) readByte() (b byte, err error) {
 		r.pending--
 		return
 	}
-	n, err := io.ReadFull(r.reader, r.pendBuf[0:1])
+	n, err := io.ReadFull(r.reader, r.pendBuf[:1])
 	if n != 1 {
 		return 0, err
 	}
 	return r.pendBuf[0], err
 }
 
-// unread saves the bytes for the next read.
-func (r *readRune) unread(buf []byte) {
-	copy(r.pendBuf[r.pending:], buf)
-	r.pending += len(buf)
-}
-
 // ReadRune returns the next UTF-8 encoded code point from the
 // io.Reader inside r.
 func (r *readRune) ReadRune() (rr rune, size int, err error) {
+	if r.peekRune >= 0 {
+		rr = r.peekRune
+		r.peekRune = ^r.peekRune
+		size = utf8.RuneLen(rr)
+		return
+	}
 	r.buf[0], err = r.readByte()
 	if err != nil {
-		return 0, 0, err
+		return
 	}
 	if r.buf[0] < utf8.RuneSelf { // fast check for common ASCII case
 		rr = rune(r.buf[0])
 		size = 1 // Known to be 1.
+		// Flip the bits of the rune so it's available to UnreadRune.
+		r.peekRune = ^rr
 		return
 	}
 	var n int
-	for n = 1; !utf8.FullRune(r.buf[0:n]); n++ {
+	for n = 1; !utf8.FullRune(r.buf[:n]); n++ {
 		r.buf[n], err = r.readByte()
 		if err != nil {
 			if err == io.EOF {
@@ -380,13 +363,25 @@ func (r *readRune) ReadRune() (rr rune, size int, err error) {
 			return
 		}
 	}
-	rr, size = utf8.DecodeRune(r.buf[0:n])
-	if size < n { // an error
-		r.unread(r.buf[size:n])
+	rr, size = utf8.DecodeRune(r.buf[:n])
+	if size < n { // an error, save the bytes for the next read
+		copy(r.pendBuf[r.pending:], r.buf[size:n])
+		r.pending += n - size
 	}
+	// Flip the bits of the rune so it's available to UnreadRune.
+	r.peekRune = ^rr
 	return
 }
 
+func (r *readRune) UnreadRune() error {
+	if r.peekRune >= 0 {
+		return errors.New("fmt: scanning called UnreadRune with no rune available")
+	}
+	// Reverse bit flip of previously read rune to obtain valid >=0 state.
+	r.peekRune = ^r.peekRune
+	return nil
+}
+
 var ssFree = sync.Pool{
 	New: func() interface{} { return new(ss) },
 }
@@ -394,15 +389,13 @@ var ssFree = sync.Pool{
 // newScanState allocates a new ss struct or grab a cached one.
 func newScanState(r io.Reader, nlIsSpace, nlIsEnd bool) (s *ss, old ssave) {
 	s = ssFree.Get().(*ss)
-	if rr, ok := r.(io.RuneReader); ok {
-		s.rr = rr
+	if rs, ok := r.(io.RuneScanner); ok {
+		s.rs = rs
 	} else {
-		s.rr = &readRune{reader: r}
+		s.rs = &readRune{reader: r, peekRune: -1}
 	}
 	s.nlIsSpace = nlIsSpace
 	s.nlIsEnd = nlIsEnd
-	s.prevRune = -1
-	s.peekRune = -1
 	s.atEOF = false
 	s.limit = hugeWid
 	s.argLimit = hugeWid
@@ -424,7 +417,7 @@ func (s *ss) free(old ssave) {
 		return
 	}
 	s.buf = s.buf[:0]
-	s.rr = nil
+	s.rs = nil
 	ssFree.Put(s)
 }
 
@@ -455,8 +448,8 @@ func (s *ss) skipSpace(stopAtNewline bool) {
 	}
 }
 
-// token returns the next space-delimited string from the input.  It
-// skips white space.  For Scanln, it stops at newlines.  For Scan,
+// token returns the next space-delimited string from the input. It
+// skips white space. For Scanln, it stops at newlines. For Scan,
 // newlines are treated as spaces.
 func (s *ss) token(skipSpace bool, f func(rune) bool) []byte {
 	if skipSpace {
@@ -525,7 +518,7 @@ func (s *ss) notEOF() {
 	s.UnreadRune()
 }
 
-// accept checks the next rune in the input.  If it's a byte (sic) in the string, it puts it in the
+// accept checks the next rune in the input. If it's a byte (sic) in the string, it puts it in the
 // buffer and returns true. Otherwise it return false.
 func (s *ss) accept(ok string) bool {
 	return s.consume(ok, true)
@@ -549,7 +542,7 @@ func (s *ss) scanBool(verb rune) bool {
 	if !s.okVerb(verb, "tv", "boolean") {
 		return false
 	}
-	// Syntax-checking a boolean is annoying.  We're not fastidious about case.
+	// Syntax-checking a boolean is annoying. We're not fastidious about case.
 	switch s.getRune() {
 	case '0':
 		return false
@@ -643,7 +636,7 @@ func (s *ss) scanBasePrefix() (base int, digits string, found bool) {
 }
 
 // scanInt returns the value of the integer represented by the next
-// token, checking for overflow.  Any error is stored in s.err.
+// token, checking for overflow. Any error is stored in s.err.
 func (s *ss) scanInt(verb rune, bitSize int) int64 {
 	if verb == 'c' {
 		return s.scanRune(bitSize)
@@ -676,7 +669,7 @@ func (s *ss) scanInt(verb rune, bitSize int) int64 {
 }
 
 // scanUint returns the value of the unsigned integer represented
-// by the next token, checking for overflow.  Any error is stored in s.err.
+// by the next token, checking for overflow. Any error is stored in s.err.
 func (s *ss) scanUint(verb rune, bitSize int) uint64 {
 	if verb == 'c' {
 		return uint64(s.scanRune(bitSize))
@@ -846,7 +839,7 @@ func (s *ss) quotedString() string {
 		return string(s.buf)
 	case '"':
 		// Double-quoted: Include the quotes and let strconv.Unquote do the backslash escapes.
-		s.buf.WriteRune(quote)
+		s.buf.WriteByte('"')
 		for {
 			r := s.mustReadRune()
 			s.buf.WriteRune(r)
@@ -922,9 +915,14 @@ func (s *ss) hexString() string {
 	return string(s.buf)
 }
 
-const floatVerbs = "beEfFgGv"
+const (
+	floatVerbs = "beEfFgGv"
 
-const hugeWid = 1 << 30
+	hugeWid = 1 << 30
+
+	intBits     = 32 << (^uint(0) >> 63)
+	uintptrBits = 32 << (^uintptr(0) >> 63)
+)
 
 // scanOne scans a single value, deriving the scanner from the type of the argument.
 func (s *ss) scanOne(verb rune, arg interface{}) {
@@ -1142,7 +1140,7 @@ func (s *ss) advance(format string) (i int) {
 }
 
 // doScanf does the real work when scanning with a format string.
-//  At the moment, it handles only pointers to basic types.
+// At the moment, it handles only pointers to basic types.
 func (s *ss) doScanf(format string, a []interface{}) (numProcessed int, err error) {
 	defer errorHandler(&err)
 	end := len(format) - 1
@@ -1155,7 +1153,7 @@ func (s *ss) doScanf(format string, a []interface{}) (numProcessed int, err erro
 		}
 		// Either we failed to advance, we have a percent character, or we ran out of input.
 		if format[i] != '%' {
-			// Can't advance format.  Why not?
+			// Can't advance format. Why not?
 			if w < 0 {
 				s.errorString("input does not match format")
 			}
diff --git a/libgo/go/fmt/scan_test.go b/libgo/go/fmt/scan_test.go
index 7ac74dcb..e36b62e 100644
--- a/libgo/go/fmt/scan_test.go
+++ b/libgo/go/fmt/scan_test.go
@@ -15,6 +15,7 @@ import (
 	"regexp"
 	"strings"
 	"testing"
+	"testing/iotest"
 	"unicode/utf8"
 )
 
@@ -78,12 +79,6 @@ var (
 	renamedComplex128Val renamedComplex128
 )
 
-type FloatTest struct {
-	text string
-	in   float64
-	out  float64
-}
-
 // Xs accepts any non-empty run of the verb character
 type Xs string
 
@@ -124,20 +119,6 @@ func (s *IntString) Scan(state ScanState, verb rune) error {
 
 var intStringVal IntString
 
-// myStringReader implements Read but not ReadRune, allowing us to test our readRune wrapper
-// type that creates something that can read runes given only Read().
-type myStringReader struct {
-	r *strings.Reader
-}
-
-func (s *myStringReader) Read(p []byte) (n int, err error) {
-	return s.r.Read(p)
-}
-
-func newReader(s string) *myStringReader {
-	return &myStringReader{strings.NewReader(s)}
-}
-
 var scanTests = []ScanTest{
 	// Basic types
 	{"T\n", &boolVal, true},  // boolean test vals toggle to be sure they are written
@@ -369,25 +350,38 @@ var multiTests = []ScanfMultiTest{
 	{"%v%v", "FALSE23", args(&truth, &i), args(false, 23), ""},
 }
 
-func testScan(name string, t *testing.T, scan func(r io.Reader, a ...interface{}) (int, error)) {
+var readers = []struct {
+	name string
+	f    func(string) io.Reader
+}{
+	{"StringReader", func(s string) io.Reader {
+		return strings.NewReader(s)
+	}},
+	{"ReaderOnly", func(s string) io.Reader {
+		return struct{ io.Reader }{strings.NewReader(s)}
+	}},
+	{"OneByteReader", func(s string) io.Reader {
+		return iotest.OneByteReader(strings.NewReader(s))
+	}},
+	{"DataErrReader", func(s string) io.Reader {
+		return iotest.DataErrReader(strings.NewReader(s))
+	}},
+}
+
+func testScan(t *testing.T, f func(string) io.Reader, scan func(r io.Reader, a ...interface{}) (int, error)) {
 	for _, test := range scanTests {
-		var r io.Reader
-		if name == "StringReader" {
-			r = strings.NewReader(test.text)
-		} else {
-			r = newReader(test.text)
-		}
+		r := f(test.text)
 		n, err := scan(r, test.in)
 		if err != nil {
 			m := ""
 			if n > 0 {
 				m = Sprintf(" (%d fields ok)", n)
 			}
-			t.Errorf("%s got error scanning %q: %s%s", name, test.text, err, m)
+			t.Errorf("got error scanning %q: %s%s", test.text, err, m)
 			continue
 		}
 		if n != 1 {
-			t.Errorf("%s count error on entry %q: got %d", name, test.text, n)
+			t.Errorf("count error on entry %q: got %d", test.text, n)
 			continue
 		}
 		// The incoming value may be a pointer
@@ -397,25 +391,25 @@ func testScan(name string, t *testing.T, scan func(r io.Reader, a ...interface{}
 		}
 		val := v.Interface()
 		if !reflect.DeepEqual(val, test.out) {
-			t.Errorf("%s scanning %q: expected %#v got %#v, type %T", name, test.text, test.out, val, val)
+			t.Errorf("scanning %q: expected %#v got %#v, type %T", test.text, test.out, val, val)
 		}
 	}
 }
 
 func TestScan(t *testing.T) {
-	testScan("StringReader", t, Fscan)
-}
-
-func TestMyReaderScan(t *testing.T) {
-	testScan("myStringReader", t, Fscan)
+	for _, r := range readers {
+		t.Run(r.name, func(t *testing.T) {
+			testScan(t, r.f, Fscan)
+		})
+	}
 }
 
 func TestScanln(t *testing.T) {
-	testScan("StringReader", t, Fscanln)
-}
-
-func TestMyReaderScanln(t *testing.T) {
-	testScan("myStringReader", t, Fscanln)
+	for _, r := range readers {
+		t.Run(r.name, func(t *testing.T) {
+			testScan(t, r.f, Fscanln)
+		})
+	}
 }
 
 func TestScanf(t *testing.T) {
@@ -506,20 +500,15 @@ func TestInf(t *testing.T) {
 	}
 }
 
-func testScanfMulti(name string, t *testing.T) {
+func testScanfMulti(t *testing.T, f func(string) io.Reader) {
 	sliceType := reflect.TypeOf(make([]interface{}, 1))
 	for _, test := range multiTests {
-		var r io.Reader
-		if name == "StringReader" {
-			r = strings.NewReader(test.text)
-		} else {
-			r = newReader(test.text)
-		}
+		r := f(test.text)
 		n, err := Fscanf(r, test.format, test.in...)
 		if err != nil {
 			if test.err == "" {
 				t.Errorf("got error scanning (%q, %q): %q", test.format, test.text, err)
-			} else if strings.Index(err.Error(), test.err) < 0 {
+			} else if !strings.Contains(err.Error(), test.err) {
 				t.Errorf("got wrong error scanning (%q, %q): %q; expected %q", test.format, test.text, err, test.err)
 			}
 			continue
@@ -545,11 +534,11 @@ func testScanfMulti(name string, t *testing.T) {
 }
 
 func TestScanfMulti(t *testing.T) {
-	testScanfMulti("StringReader", t)
-}
-
-func TestMyReaderScanfMulti(t *testing.T) {
-	testScanfMulti("myStringReader", t)
+	for _, r := range readers {
+		t.Run(r.name, func(t *testing.T) {
+			testScanfMulti(t, r.f)
+		})
+	}
 }
 
 func TestScanMultiple(t *testing.T) {
@@ -613,7 +602,7 @@ func TestScanNotPointer(t *testing.T) {
 	_, err := Fscan(r, a)
 	if err == nil {
 		t.Error("expected error scanning non-pointer")
-	} else if strings.Index(err.Error(), "pointer") < 0 {
+	} else if !strings.Contains(err.Error(), "pointer") {
 		t.Errorf("expected pointer error scanning non-pointer, got: %s", err)
 	}
 }
@@ -623,7 +612,7 @@ func TestScanlnNoNewline(t *testing.T) {
 	_, err := Sscanln("1 x\n", &a)
 	if err == nil {
 		t.Error("expected error scanning string missing newline")
-	} else if strings.Index(err.Error(), "newline") < 0 {
+	} else if !strings.Contains(err.Error(), "newline") {
 		t.Errorf("expected newline error scanning string missing newline, got: %s", err)
 	}
 }
@@ -634,7 +623,7 @@ func TestScanlnWithMiddleNewline(t *testing.T) {
 	_, err := Fscanln(r, &a, &b)
 	if err == nil {
 		t.Error("expected error scanning string with extra newline")
-	} else if strings.Index(err.Error(), "newline") < 0 {
+	} else if !strings.Contains(err.Error(), "newline") {
 		t.Errorf("expected newline error scanning string with extra newline, got: %s", err)
 	}
 }
@@ -767,7 +756,7 @@ func TestUnreadRuneWithBufio(t *testing.T) {
 
 type TwoLines string
 
-// Scan attempts to read two lines into the object.  Scanln should prevent this
+// Scan attempts to read two lines into the object. Scanln should prevent this
 // because it stops at newline; Scan and Scanf should be fine.
 func (t *TwoLines) Scan(state ScanState, verb rune) error {
 	chars := make([]rune, 0, 100)
@@ -824,20 +813,10 @@ func TestMultiLine(t *testing.T) {
 	}
 }
 
-// simpleReader is a strings.Reader that implements only Read, not ReadRune.
-// Good for testing readahead.
-type simpleReader struct {
-	sr *strings.Reader
-}
-
-func (s *simpleReader) Read(b []byte) (n int, err error) {
-	return s.sr.Read(b)
-}
-
 // TestLineByLineFscanf tests that Fscanf does not read past newline. Issue
 // 3481.
 func TestLineByLineFscanf(t *testing.T) {
-	r := &simpleReader{strings.NewReader("1\n2\n")}
+	r := struct{ io.Reader }{strings.NewReader("1\n2\n")}
 	var i, j int
 	n, err := Fscanf(r, "%v\n", &i)
 	if n != 1 || err != nil {
@@ -1001,6 +980,18 @@ func BenchmarkScanRecursiveInt(b *testing.B) {
 	}
 }
 
+func BenchmarkScanRecursiveIntReaderWrapper(b *testing.B) {
+	b.ResetTimer()
+	ints := makeInts(intCount)
+	var r RecursiveInt
+	for i := b.N - 1; i >= 0; i-- {
+		buf := struct{ io.Reader }{strings.NewReader(string(ints))}
+		b.StartTimer()
+		Fscan(buf, &r)
+		b.StopTimer()
+	}
+}
+
 // Issue 9124.
 // %x on bytes couldn't handle non-space bytes terminating the scan.
 func TestHexBytes(t *testing.T) {