libgo: update to Go 1.8 release candidate 1

    
    Compiler changes:
      * Change map assignment to use mapassign and assign value directly.
      * Change string iteration to use decoderune, faster for ASCII strings.
      * Change makeslice to take int, and use makeslice64 for larger values.
      * Add new noverflow field to hmap struct used for maps.
    
    Unresolved problems, to be fixed later:
      * Commented out test in go/types/sizes_test.go that doesn't compile.
      * Commented out reflect.TestStructOf test for padding after zero-sized field.
    
    Reviewed-on: https://go-review.googlesource.com/35231

gotools/:
	Updates for Go 1.8rc1.
	* Makefile.am (go_cmd_go_files): Add bug.go.
	(s-zdefaultcc): Write defaultPkgConfig.
	* Makefile.in: Rebuild.

From-SVN: r244456

13 files changed, 735 insertions, 159 deletions

diff --git a/libgo/go/image/color/color.go b/libgo/go/image/color/color.go
index 1044339..0832c59 100644
--- a/libgo/go/image/color/color.go
+++ b/libgo/go/image/color/color.go
@@ -246,8 +246,18 @@ func grayModel(c Color) Color {
 		return c
 	}
 	r, g, b, _ := c.RGBA()
-	y := (299*r + 587*g + 114*b + 500) / 1000
-	return Gray{uint8(y >> 8)}
+
+	// These coefficients (the fractions 0.299, 0.587 and 0.114) are the same
+	// as those given by the JFIF specification and used by func RGBToYCbCr in
+	// ycbcr.go.
+	//
+	// Note that 19595 + 38470 + 7471 equals 65536.
+	//
+	// The 24 is 16 + 8. The 16 is the same as used in RGBToYCbCr. The 8 is
+	// because the return value is 8 bit color, not 16 bit color.
+	y := (19595*r + 38470*g + 7471*b + 1<<15) >> 24
+
+	return Gray{uint8(y)}
 }
 
 func gray16Model(c Color) Color {
@@ -255,7 +265,14 @@ func gray16Model(c Color) Color {
 		return c
 	}
 	r, g, b, _ := c.RGBA()
-	y := (299*r + 587*g + 114*b + 500) / 1000
+
+	// These coefficients (the fractions 0.299, 0.587 and 0.114) are the same
+	// as those given by the JFIF specification and used by func RGBToYCbCr in
+	// ycbcr.go.
+	//
+	// Note that 19595 + 38470 + 7471 equals 65536.
+	y := (19595*r + 38470*g + 7471*b + 1<<15) >> 16
+
 	return Gray16{uint16(y)}
 }
 
diff --git a/libgo/go/image/color/ycbcr.go b/libgo/go/image/color/ycbcr.go
index 3df5d367..18d1a56 100644
--- a/libgo/go/image/color/ycbcr.go
+++ b/libgo/go/image/color/ycbcr.go
@@ -17,6 +17,8 @@ func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8) {
 	b1 := int32(b)
 
 	// yy is in range [0,0xff].
+	//
+	// Note that 19595 + 38470 + 7471 equals 65536.
 	yy := (19595*r1 + 38470*g1 + 7471*b1 + 1<<15) >> 16
 
 	// The bit twiddling below is equivalent to
@@ -32,6 +34,8 @@ func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8) {
 	// Note that the uint8 type conversion in the return
 	// statement will convert ^int32(0) to 0xff.
 	// The code below to compute cr uses a similar pattern.
+	//
+	// Note that -11056 - 21712 + 32768 equals 0.
 	cb := -11056*r1 - 21712*g1 + 32768*b1 + 257<<15
 	if uint32(cb)&0xff000000 == 0 {
 		cb >>= 16
@@ -39,6 +43,7 @@ func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8) {
 		cb = ^(cb >> 31)
 	}
 
+	// Note that 32768 - 27440 - 5328 equals 0.
 	cr := 32768*r1 - 27440*g1 - 5328*b1 + 257<<15
 	if uint32(cr)&0xff000000 == 0 {
 		cr >>= 16
@@ -134,24 +139,39 @@ func (c YCbCr) RGBA() (uint32, uint32, uint32, uint32) {
 	yy1 := int32(c.Y) * 0x10100 // Convert 0x12 to 0x121200.
 	cb1 := int32(c.Cb) - 128
 	cr1 := int32(c.Cr) - 128
-	r := (yy1 + 91881*cr1) >> 8
-	g := (yy1 - 22554*cb1 - 46802*cr1) >> 8
-	b := (yy1 + 116130*cb1) >> 8
-	if r < 0 {
-		r = 0
-	} else if r > 0xffff {
-		r = 0xffff
+
+	// The bit twiddling below is equivalent to
+	//
+	// r := (yy1 + 91881*cr1) >> 8
+	// if r < 0 {
+	//     r = 0
+	// } else if r > 0xff {
+	//     r = 0xffff
+	// }
+	//
+	// but uses fewer branches and is faster.
+	// The code below to compute g and b uses a similar pattern.
+	r := yy1 + 91881*cr1
+	if uint32(r)&0xff000000 == 0 {
+		r >>= 8
+	} else {
+		r = ^(r >> 31) & 0xffff
 	}
-	if g < 0 {
-		g = 0
-	} else if g > 0xffff {
-		g = 0xffff
+
+	g := yy1 - 22554*cb1 - 46802*cr1
+	if uint32(g)&0xff000000 == 0 {
+		g >>= 8
+	} else {
+		g = ^(g >> 31) & 0xffff
 	}
-	if b < 0 {
-		b = 0
-	} else if b > 0xffff {
-		b = 0xffff
+
+	b := yy1 + 116130*cb1
+	if uint32(b)&0xff000000 == 0 {
+		b >>= 8
+	} else {
+		b = ^(b >> 31) & 0xffff
 	}
+
 	return uint32(r), uint32(g), uint32(b), 0xffff
 }
 
@@ -179,23 +199,37 @@ func (c NYCbCrA) RGBA() (uint32, uint32, uint32, uint32) {
 	yy1 := int32(c.Y) * 0x10100 // Convert 0x12 to 0x121200.
 	cb1 := int32(c.Cb) - 128
 	cr1 := int32(c.Cr) - 128
-	r := (yy1 + 91881*cr1) >> 8
-	g := (yy1 - 22554*cb1 - 46802*cr1) >> 8
-	b := (yy1 + 116130*cb1) >> 8
-	if r < 0 {
-		r = 0
-	} else if r > 0xffff {
-		r = 0xffff
+
+	// The bit twiddling below is equivalent to
+	//
+	// r := (yy1 + 91881*cr1) >> 8
+	// if r < 0 {
+	//     r = 0
+	// } else if r > 0xff {
+	//     r = 0xffff
+	// }
+	//
+	// but uses fewer branches and is faster.
+	// The code below to compute g and b uses a similar pattern.
+	r := yy1 + 91881*cr1
+	if uint32(r)&0xff000000 == 0 {
+		r >>= 8
+	} else {
+		r = ^(r >> 31) & 0xffff
 	}
-	if g < 0 {
-		g = 0
-	} else if g > 0xffff {
-		g = 0xffff
+
+	g := yy1 - 22554*cb1 - 46802*cr1
+	if uint32(g)&0xff000000 == 0 {
+		g >>= 8
+	} else {
+		g = ^(g >> 31) & 0xffff
 	}
-	if b < 0 {
-		b = 0
-	} else if b > 0xffff {
-		b = 0xffff
+
+	b := yy1 + 116130*cb1
+	if uint32(b)&0xff000000 == 0 {
+		b >>= 8
+	} else {
+		b = ^(b >> 31) & 0xffff
 	}
 
 	// The second part of this method applies the alpha.
diff --git a/libgo/go/image/color/ycbcr_test.go b/libgo/go/image/color/ycbcr_test.go
index 561699f..85c1b98 100644
--- a/libgo/go/image/color/ycbcr_test.go
+++ b/libgo/go/image/color/ycbcr_test.go
@@ -172,7 +172,8 @@ func TestPalette(t *testing.T) {
 	}
 }
 
-var sink uint8
+var sink8 uint8
+var sink32 uint32
 
 func BenchmarkYCbCrToRGB(b *testing.B) {
 	// YCbCrToRGB does saturating arithmetic.
@@ -180,17 +181,17 @@ func BenchmarkYCbCrToRGB(b *testing.B) {
 	// different paths through the generated code.
 	b.Run("0", func(b *testing.B) {
 		for i := 0; i < b.N; i++ {
-			sink, sink, sink = YCbCrToRGB(0, 0, 0)
+			sink8, sink8, sink8 = YCbCrToRGB(0, 0, 0)
 		}
 	})
 	b.Run("128", func(b *testing.B) {
 		for i := 0; i < b.N; i++ {
-			sink, sink, sink = YCbCrToRGB(128, 128, 128)
+			sink8, sink8, sink8 = YCbCrToRGB(128, 128, 128)
 		}
 	})
 	b.Run("255", func(b *testing.B) {
 		for i := 0; i < b.N; i++ {
-			sink, sink, sink = YCbCrToRGB(255, 255, 255)
+			sink8, sink8, sink8 = YCbCrToRGB(255, 255, 255)
 		}
 	})
 }
@@ -201,17 +202,65 @@ func BenchmarkRGBToYCbCr(b *testing.B) {
 	// through the generated code.
 	b.Run("0", func(b *testing.B) {
 		for i := 0; i < b.N; i++ {
-			sink, sink, sink = RGBToYCbCr(0, 0, 0)
+			sink8, sink8, sink8 = RGBToYCbCr(0, 0, 0)
 		}
 	})
 	b.Run("Cb", func(b *testing.B) {
 		for i := 0; i < b.N; i++ {
-			sink, sink, sink = RGBToYCbCr(0, 0, 255)
+			sink8, sink8, sink8 = RGBToYCbCr(0, 0, 255)
 		}
 	})
 	b.Run("Cr", func(b *testing.B) {
 		for i := 0; i < b.N; i++ {
-			sink, sink, sink = RGBToYCbCr(255, 0, 0)
+			sink8, sink8, sink8 = RGBToYCbCr(255, 0, 0)
+		}
+	})
+}
+
+func BenchmarkYCbCrToRGBA(b *testing.B) {
+	// RGB does saturating arithmetic.
+	// Low, middle, and high values can take
+	// different paths through the generated code.
+	b.Run("0", func(b *testing.B) {
+		c := YCbCr{0, 0, 0}
+		for i := 0; i < b.N; i++ {
+			sink32, sink32, sink32, sink32 = c.RGBA()
+		}
+	})
+	b.Run("128", func(b *testing.B) {
+		c := YCbCr{128, 128, 128}
+		for i := 0; i < b.N; i++ {
+			sink32, sink32, sink32, sink32 = c.RGBA()
+		}
+	})
+	b.Run("255", func(b *testing.B) {
+		c := YCbCr{255, 255, 255}
+		for i := 0; i < b.N; i++ {
+			sink32, sink32, sink32, sink32 = c.RGBA()
+		}
+	})
+}
+
+func BenchmarkNYCbCrAToRGBA(b *testing.B) {
+	// RGBA does saturating arithmetic.
+	// Low, middle, and high values can take
+	// different paths through the generated code.
+	b.Run("0", func(b *testing.B) {
+		c := NYCbCrA{YCbCr{0, 0, 0}, 0xff}
+		for i := 0; i < b.N; i++ {
+			sink32, sink32, sink32, sink32 = c.RGBA()
+		}
+	})
+	b.Run("128", func(b *testing.B) {
+		c := NYCbCrA{YCbCr{128, 128, 128}, 0xff}
+		for i := 0; i < b.N; i++ {
+			sink32, sink32, sink32, sink32 = c.RGBA()
+		}
+	})
+	b.Run("255", func(b *testing.B) {
+		c := NYCbCrA{YCbCr{255, 255, 255}, 0xff}
+		for i := 0; i < b.N; i++ {
+			sink32, sink32, sink32, sink32 = c.RGBA()
 		}
 	})
 }
diff --git a/libgo/go/image/draw/bench_test.go b/libgo/go/image/draw/bench_test.go
index 7b89f95..a41d7e7 100644
--- a/libgo/go/image/draw/bench_test.go
+++ b/libgo/go/image/draw/bench_test.go
@@ -74,7 +74,7 @@ func bench(b *testing.B, dcm, scm, mcm color.Model, op Op) {
 	var src image.Image
 	switch scm {
 	case nil:
-		src = &image.Uniform{C: color.RGBA{0x11, 0x22, 0x33, 0xff}}
+		src = &image.Uniform{C: color.RGBA{0x11, 0x22, 0x33, 0x44}}
 	case color.CMYKModel:
 		src1 := image.NewCMYK(image.Rect(0, 0, srcw, srch))
 		for y := 0; y < srch; y++ {
diff --git a/libgo/go/image/draw/draw.go b/libgo/go/image/draw/draw.go
index 6a16cd3..a31dd42 100644
--- a/libgo/go/image/draw/draw.go
+++ b/libgo/go/image/draw/draw.go
@@ -116,7 +116,12 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
 			if mask == nil {
 				switch src0 := src.(type) {
 				case *image.Uniform:
-					drawFillOver(dst0, r, src0)
+					sr, sg, sb, sa := src0.RGBA()
+					if sa == 0xffff {
+						drawFillSrc(dst0, r, sr, sg, sb, sa)
+					} else {
+						drawFillOver(dst0, r, sr, sg, sb, sa)
+					}
 					return
 				case *image.RGBA:
 					drawCopyOver(dst0, r, src0, sp)
@@ -150,7 +155,8 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
 			if mask == nil {
 				switch src0 := src.(type) {
 				case *image.Uniform:
-					drawFillSrc(dst0, r, src0)
+					sr, sg, sb, sa := src0.RGBA()
+					drawFillSrc(dst0, r, sr, sg, sb, sa)
 					return
 				case *image.RGBA:
 					drawCopySrc(dst0, r, src0, sp)
@@ -232,8 +238,7 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
 	}
 }
 
-func drawFillOver(dst *image.RGBA, r image.Rectangle, src *image.Uniform) {
-	sr, sg, sb, sa := src.RGBA()
+func drawFillOver(dst *image.RGBA, r image.Rectangle, sr, sg, sb, sa uint32) {
 	// The 0x101 is here for the same reason as in drawRGBA.
 	a := (m - sa) * 0x101
 	i0 := dst.PixOffset(r.Min.X, r.Min.Y)
@@ -255,8 +260,7 @@ func drawFillOver(dst *image.RGBA, r image.Rectangle, src *image.Uniform) {
 	}
 }
 
-func drawFillSrc(dst *image.RGBA, r image.Rectangle, src *image.Uniform) {
-	sr, sg, sb, sa := src.RGBA()
+func drawFillSrc(dst *image.RGBA, r image.Rectangle, sr, sg, sb, sa uint32) {
 	sr8 := uint8(sr >> 8)
 	sg8 := uint8(sg >> 8)
 	sb8 := uint8(sb >> 8)
diff --git a/libgo/go/image/draw/example_test.go b/libgo/go/image/draw/example_test.go
new file mode 100644
index 0000000..d381c1c
--- /dev/null
+++ b/libgo/go/image/draw/example_test.go
@@ -0,0 +1,50 @@
+// Copyright 2016 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.
+
+// +build ignore
+
+package draw_test
+
+import (
+	"fmt"
+	"image"
+	"image/color"
+	"image/draw"
+	"math"
+)
+
+func ExampleDrawer_floydSteinberg() {
+	const width = 130
+	const height = 50
+
+	im := image.NewGray(image.Rectangle{Max: image.Point{X: width, Y: height}})
+	for x := 0; x < width; x++ {
+		for y := 0; y < height; y++ {
+			dist := math.Sqrt(math.Pow(float64(x-width/2), 2)/3+math.Pow(float64(y-height/2), 2)) / (height / 1.5) * 255
+			var gray uint8
+			if dist > 255 {
+				gray = 255
+			} else {
+				gray = uint8(dist)
+			}
+			im.SetGray(x, y, color.Gray{Y: 255 - gray})
+		}
+	}
+	pi := image.NewPaletted(im.Bounds(), []color.Color{
+		color.Gray{Y: 255},
+		color.Gray{Y: 160},
+		color.Gray{Y: 70},
+		color.Gray{Y: 35},
+		color.Gray{Y: 0},
+	})
+
+	draw.FloydSteinberg.Draw(pi, im.Bounds(), im, image.ZP)
+	shade := []string{" ", "░", "▒", "▓", "█"}
+	for i, p := range pi.Pix {
+		fmt.Print(shade[p])
+		if (i+1)%width == 0 {
+			fmt.Print("\n")
+		}
+	}
+}
diff --git a/libgo/go/image/gif/reader.go b/libgo/go/image/gif/reader.go
index 6181a94..e6111281 100644
--- a/libgo/go/image/gif/reader.go
+++ b/libgo/go/image/gif/reader.go
@@ -63,6 +63,22 @@ const (
 	eApplication    = 0xFF // Application
 )
 
+func readFull(r io.Reader, b []byte) error {
+	_, err := io.ReadFull(r, b)
+	if err == io.EOF {
+		err = io.ErrUnexpectedEOF
+	}
+	return err
+}
+
+func readByte(r io.ByteReader) (byte, error) {
+	b, err := r.ReadByte()
+	if err == io.EOF {
+		err = io.ErrUnexpectedEOF
+	}
+	return b, err
+}
+
 // decoder is the type used to decode a GIF file.
 type decoder struct {
 	r reader
@@ -124,7 +140,7 @@ func (b *blockReader) Read(p []byte) (int, error) {
 			return 0, b.err
 		}
 		b.slice = b.tmp[:blockLen]
-		if _, b.err = io.ReadFull(b.r, b.slice); b.err != nil {
+		if b.err = readFull(b.r, b.slice); b.err != nil {
 			return 0, b.err
 		}
 	}
@@ -151,9 +167,9 @@ func (d *decoder) decode(r io.Reader, configOnly bool) error {
 	}
 
 	for {
-		c, err := d.r.ReadByte()
+		c, err := readByte(d.r)
 		if err != nil {
-			return err
+			return fmt.Errorf("gif: reading frames: %v", err)
 		}
 		switch c {
 		case sExtension:
@@ -198,9 +214,9 @@ func (d *decoder) decode(r io.Reader, configOnly bool) error {
 					m.Palette = p
 				}
 			}
-			litWidth, err := d.r.ReadByte()
+			litWidth, err := readByte(d.r)
 			if err != nil {
-				return err
+				return fmt.Errorf("gif: reading image data: %v", err)
 			}
 			if litWidth < 2 || litWidth > 8 {
 				return fmt.Errorf("gif: pixel size in decode out of range: %d", litWidth)
@@ -209,9 +225,9 @@ func (d *decoder) decode(r io.Reader, configOnly bool) error {
 			br := &blockReader{r: d.r}
 			lzwr := lzw.NewReader(br, lzw.LSB, int(litWidth))
 			defer lzwr.Close()
-			if _, err = io.ReadFull(lzwr, m.Pix); err != nil {
+			if err = readFull(lzwr, m.Pix); err != nil {
 				if err != io.ErrUnexpectedEOF {
-					return err
+					return fmt.Errorf("gif: reading image data: %v", err)
 				}
 				return errNotEnough
 			}
@@ -228,13 +244,13 @@ func (d *decoder) decode(r io.Reader, configOnly bool) error {
 			// See https://golang.org/issue/9856 for an example GIF.
 			if n, err := lzwr.Read(d.tmp[:1]); n != 0 || (err != io.EOF && err != io.ErrUnexpectedEOF) {
 				if err != nil {
-					return err
+					return fmt.Errorf("gif: reading image data: %v", err)
 				}
 				return errTooMuch
 			}
 			if n, err := br.Read(d.tmp[:1]); n != 0 || err != io.EOF {
 				if err != nil {
-					return err
+					return fmt.Errorf("gif: reading image data: %v", err)
 				}
 				return errTooMuch
 			}
@@ -264,7 +280,7 @@ func (d *decoder) decode(r io.Reader, configOnly bool) error {
 
 		case sTrailer:
 			if len(d.image) == 0 {
-				return io.ErrUnexpectedEOF
+				return fmt.Errorf("gif: missing image data")
 			}
 			return nil
 
@@ -275,13 +291,13 @@ func (d *decoder) decode(r io.Reader, configOnly bool) error {
 }
 
 func (d *decoder) readHeaderAndScreenDescriptor() error {
-	_, err := io.ReadFull(d.r, d.tmp[:13])
+	err := readFull(d.r, d.tmp[:13])
 	if err != nil {
-		return err
+		return fmt.Errorf("gif: reading header: %v", err)
 	}
 	d.vers = string(d.tmp[:6])
 	if d.vers != "GIF87a" && d.vers != "GIF89a" {
-		return fmt.Errorf("gif: can't recognize format %s", d.vers)
+		return fmt.Errorf("gif: can't recognize format %q", d.vers)
 	}
 	d.width = int(d.tmp[6]) + int(d.tmp[7])<<8
 	d.height = int(d.tmp[8]) + int(d.tmp[9])<<8
@@ -298,9 +314,9 @@ func (d *decoder) readHeaderAndScreenDescriptor() error {
 
 func (d *decoder) readColorTable(fields byte) (color.Palette, error) {
 	n := 1 << (1 + uint(fields&fColorTableBitsMask))
-	_, err := io.ReadFull(d.r, d.tmp[:3*n])
+	err := readFull(d.r, d.tmp[:3*n])
 	if err != nil {
-		return nil, fmt.Errorf("gif: short read on color table: %s", err)
+		return nil, fmt.Errorf("gif: reading color table: %s", err)
 	}
 	j, p := 0, make(color.Palette, n)
 	for i := range p {
@@ -311,9 +327,9 @@ func (d *decoder) readColorTable(fields byte) (color.Palette, error) {
 }
 
 func (d *decoder) readExtension() error {
-	extension, err := d.r.ReadByte()
+	extension, err := readByte(d.r)
 	if err != nil {
-		return err
+		return fmt.Errorf("gif: reading extension: %v", err)
 	}
 	size := 0
 	switch extension {
@@ -324,9 +340,9 @@ func (d *decoder) readExtension() error {
 	case eComment:
 		// nothing to do but read the data.
 	case eApplication:
-		b, err := d.r.ReadByte()
+		b, err := readByte(d.r)
 		if err != nil {
-			return err
+			return fmt.Errorf("gif: reading extension: %v", err)
 		}
 		// The spec requires size be 11, but Adobe sometimes uses 10.
 		size = int(b)
@@ -334,8 +350,8 @@ func (d *decoder) readExtension() error {
 		return fmt.Errorf("gif: unknown extension 0x%.2x", extension)
 	}
 	if size > 0 {
-		if _, err := io.ReadFull(d.r, d.tmp[:size]); err != nil {
-			return err
+		if err := readFull(d.r, d.tmp[:size]); err != nil {
+			return fmt.Errorf("gif: reading extension: %v", err)
 		}
 	}
 
@@ -343,8 +359,11 @@ func (d *decoder) readExtension() error {
 	// this extension defines a loop count.
 	if extension == eApplication && string(d.tmp[:size]) == "NETSCAPE2.0" {
 		n, err := d.readBlock()
-		if n == 0 || err != nil {
-			return err
+		if err != nil {
+			return fmt.Errorf("gif: reading extension: %v", err)
+		}
+		if n == 0 {
+			return nil
 		}
 		if n == 3 && d.tmp[0] == 1 {
 			d.loopCount = int(d.tmp[1]) | int(d.tmp[2])<<8
@@ -352,14 +371,17 @@ func (d *decoder) readExtension() error {
 	}
 	for {
 		n, err := d.readBlock()
-		if n == 0 || err != nil {
-			return err
+		if err != nil {
+			return fmt.Errorf("gif: reading extension: %v", err)
+		}
+		if n == 0 {
+			return nil
 		}
 	}
 }
 
 func (d *decoder) readGraphicControl() error {
-	if _, err := io.ReadFull(d.r, d.tmp[:6]); err != nil {
+	if err := readFull(d.r, d.tmp[:6]); err != nil {
 		return fmt.Errorf("gif: can't read graphic control: %s", err)
 	}
 	if d.tmp[0] != 4 {
@@ -379,7 +401,7 @@ func (d *decoder) readGraphicControl() error {
 }
 
 func (d *decoder) newImageFromDescriptor() (*image.Paletted, error) {
-	if _, err := io.ReadFull(d.r, d.tmp[:9]); err != nil {
+	if err := readFull(d.r, d.tmp[:9]); err != nil {
 		return nil, fmt.Errorf("gif: can't read image descriptor: %s", err)
 	}
 	left := int(d.tmp[0]) + int(d.tmp[1])<<8
@@ -399,11 +421,14 @@ func (d *decoder) newImageFromDescriptor() (*image.Paletted, error) {
 }
 
 func (d *decoder) readBlock() (int, error) {
-	n, err := d.r.ReadByte()
+	n, err := readByte(d.r)
 	if n == 0 || err != nil {
 		return 0, err
 	}
-	return io.ReadFull(d.r, d.tmp[:n])
+	if err := readFull(d.r, d.tmp[:n]); err != nil {
+		return 0, err
+	}
+	return int(n), nil
 }
 
 // interlaceScan defines the ordering for a pass of the interlace algorithm.
diff --git a/libgo/go/image/gif/reader_test.go b/libgo/go/image/gif/reader_test.go
index 90c8149..1267ba0 100644
--- a/libgo/go/image/gif/reader_test.go
+++ b/libgo/go/image/gif/reader_test.go
@@ -10,6 +10,7 @@ import (
 	"image"
 	"image/color"
 	"reflect"
+	"strings"
 	"testing"
 )
 
@@ -292,3 +293,19 @@ func TestLoopCount(t *testing.T) {
 		t.Errorf("loop count mismatch: %d vs %d", img.LoopCount, img1.LoopCount)
 	}
 }
+
+func TestUnexpectedEOF(t *testing.T) {
+	for i := len(testGIF) - 1; i >= 0; i-- {
+		_, err := Decode(bytes.NewReader(testGIF[:i]))
+		if err == errNotEnough {
+			continue
+		}
+		text := ""
+		if err != nil {
+			text = err.Error()
+		}
+		if !strings.HasPrefix(text, "gif:") || !strings.HasSuffix(text, ": unexpected EOF") {
+			t.Errorf("Decode(testGIF[:%d]) = %v, want gif: ...: unexpected EOF", i, err)
+		}
+	}
+}
diff --git a/libgo/go/image/png/example_test.go b/libgo/go/image/png/example_test.go
new file mode 100644
index 0000000..2a03be5
--- /dev/null
+++ b/libgo/go/image/png/example_test.go
@@ -0,0 +1,79 @@
+// Copyright 2016 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.
+
+// +build ignore
+
+package png_test
+
+import (
+	"encoding/base64"
+	"fmt"
+	"image"
+	"image/color"
+	"image/png"
+	"io"
+	"log"
+	"os"
+	"strings"
+)
+
+const gopher = `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`
+
+// gopherPNG creates an io.Reader by decoding the base64 encoded image data string in the gopher constant.
+func gopherPNG() io.Reader { return base64.NewDecoder(base64.StdEncoding, strings.NewReader(gopher)) }
+
+func ExampleDecode() {
+	// This example uses png.Decode which can only decode PNG images.
+	// Consider using the general image.Decode as it can sniff and decode any registered image format.
+	img, err := png.Decode(gopherPNG())
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	levels := []string{" ", "░", "▒", "▓", "█"}
+
+	for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ {
+		for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ {
+			c := color.GrayModel.Convert(img.At(x, y)).(color.Gray)
+			level := c.Y / 51 // 51 * 5 = 255
+			if level == 5 {
+				level--
+			}
+			fmt.Print(levels[level])
+		}
+		fmt.Print("\n")
+	}
+}
+
+func ExampleEncode() {
+	const width, height = 256, 256
+
+	// Create a colored image of the given width and height.
+	img := image.NewNRGBA(image.Rect(0, 0, width, height))
+
+	for y := 0; y < height; y++ {
+		for x := 0; x < width; x++ {
+			img.Set(x, y, color.NRGBA{
+				R: uint8((x + y) & 255),
+				G: uint8((x + y) << 1 & 255),
+				B: uint8((x + y) << 2 & 255),
+				A: 255,
+			})
+		}
+	}
+
+	f, err := os.Create("image.png")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if err := png.Encode(f, img); err != nil {
+		f.Close()
+		log.Fatal(err)
+	}
+
+	if err := f.Close(); err != nil {
+		log.Fatal(err)
+	}
+}
diff --git a/libgo/go/image/png/reader.go b/libgo/go/image/png/reader.go
index 2dd5ed8..32f78f0 100644
--- a/libgo/go/image/png/reader.go
+++ b/libgo/go/image/png/reader.go
@@ -113,6 +113,11 @@ type decoder struct {
 	idatLength    uint32
 	tmp           [3 * 256]byte
 	interlace     int
+
+	// useTransparent and transparent are used for grayscale and truecolor
+	// transparency, as opposed to palette transparency.
+	useTransparent bool
+	transparent    [6]byte
 }
 
 // A FormatError reports that the input is not a valid PNG.
@@ -252,20 +257,51 @@ func (d *decoder) parsePLTE(length uint32) error {
 }
 
 func (d *decoder) parsetRNS(length uint32) error {
-	if length > 256 {
-		return FormatError("bad tRNS length")
-	}
-	n, err := io.ReadFull(d.r, d.tmp[:length])
-	if err != nil {
-		return err
-	}
-	d.crc.Write(d.tmp[:n])
 	switch d.cb {
-	case cbG8, cbG16:
-		return UnsupportedError("grayscale transparency")
+	case cbG1, cbG2, cbG4, cbG8, cbG16:
+		if length != 2 {
+			return FormatError("bad tRNS length")
+		}
+		n, err := io.ReadFull(d.r, d.tmp[:length])
+		if err != nil {
+			return err
+		}
+		d.crc.Write(d.tmp[:n])
+
+		copy(d.transparent[:], d.tmp[:length])
+		switch d.cb {
+		case cbG1:
+			d.transparent[1] *= 0xff
+		case cbG2:
+			d.transparent[1] *= 0x55
+		case cbG4:
+			d.transparent[1] *= 0x11
+		}
+		d.useTransparent = true
+
 	case cbTC8, cbTC16:
-		return UnsupportedError("truecolor transparency")
+		if length != 6 {
+			return FormatError("bad tRNS length")
+		}
+		n, err := io.ReadFull(d.r, d.tmp[:length])
+		if err != nil {
+			return err
+		}
+		d.crc.Write(d.tmp[:n])
+
+		copy(d.transparent[:], d.tmp[:length])
+		d.useTransparent = true
+
 	case cbP1, cbP2, cbP4, cbP8:
+		if length > 256 {
+			return FormatError("bad tRNS length")
+		}
+		n, err := io.ReadFull(d.r, d.tmp[:length])
+		if err != nil {
+			return err
+		}
+		d.crc.Write(d.tmp[:n])
+
 		if len(d.palette) < n {
 			d.palette = d.palette[:n]
 		}
@@ -273,7 +309,8 @@ func (d *decoder) parsetRNS(length uint32) error {
 			rgba := d.palette[i].(color.RGBA)
 			d.palette[i] = color.NRGBA{rgba.R, rgba.G, rgba.B, d.tmp[i]}
 		}
-	case cbGA8, cbGA16, cbTCA8, cbTCA16:
+
+	default:
 		return FormatError("tRNS, color type mismatch")
 	}
 	return d.verifyChecksum()
@@ -366,7 +403,7 @@ func (d *decoder) decode() (image.Image, error) {
 
 // readImagePass reads a single image pass, sized according to the pass number.
 func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image.Image, error) {
-	var bitsPerPixel int = 0
+	bitsPerPixel := 0
 	pixOffset := 0
 	var (
 		gray     *image.Gray
@@ -394,16 +431,26 @@ func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image
 	switch d.cb {
 	case cbG1, cbG2, cbG4, cbG8:
 		bitsPerPixel = d.depth
-		gray = image.NewGray(image.Rect(0, 0, width, height))
-		img = gray
+		if d.useTransparent {
+			nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
+			img = nrgba
+		} else {
+			gray = image.NewGray(image.Rect(0, 0, width, height))
+			img = gray
+		}
 	case cbGA8:
 		bitsPerPixel = 16
 		nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
 		img = nrgba
 	case cbTC8:
 		bitsPerPixel = 24
-		rgba = image.NewRGBA(image.Rect(0, 0, width, height))
-		img = rgba
+		if d.useTransparent {
+			nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
+			img = nrgba
+		} else {
+			rgba = image.NewRGBA(image.Rect(0, 0, width, height))
+			img = rgba
+		}
 	case cbP1, cbP2, cbP4, cbP8:
 		bitsPerPixel = d.depth
 		paletted = image.NewPaletted(image.Rect(0, 0, width, height), d.palette)
@@ -414,16 +461,26 @@ func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image
 		img = nrgba
 	case cbG16:
 		bitsPerPixel = 16
-		gray16 = image.NewGray16(image.Rect(0, 0, width, height))
-		img = gray16
+		if d.useTransparent {
+			nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
+			img = nrgba64
+		} else {
+			gray16 = image.NewGray16(image.Rect(0, 0, width, height))
+			img = gray16
+		}
 	case cbGA16:
 		bitsPerPixel = 32
 		nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
 		img = nrgba64
 	case cbTC16:
 		bitsPerPixel = 48
-		rgba64 = image.NewRGBA64(image.Rect(0, 0, width, height))
-		img = rgba64
+		if d.useTransparent {
+			nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
+			img = nrgba64
+		} else {
+			rgba64 = image.NewRGBA64(image.Rect(0, 0, width, height))
+			img = rgba64
+		}
 	case cbTCA16:
 		bitsPerPixel = 64
 		nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
@@ -483,27 +540,75 @@ func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image
 		// Convert from bytes to colors.
 		switch d.cb {
 		case cbG1:
-			for x := 0; x < width; x += 8 {
-				b := cdat[x/8]
-				for x2 := 0; x2 < 8 && x+x2 < width; x2++ {
-					gray.SetGray(x+x2, y, color.Gray{(b >> 7) * 0xff})
-					b <<= 1
+			if d.useTransparent {
+				ty := d.transparent[1]
+				for x := 0; x < width; x += 8 {
+					b := cdat[x/8]
+					for x2 := 0; x2 < 8 && x+x2 < width; x2++ {
+						ycol := (b >> 7) * 0xff
+						acol := uint8(0xff)
+						if ycol == ty {
+							acol = 0x00
+						}
+						nrgba.SetNRGBA(x+x2, y, color.NRGBA{ycol, ycol, ycol, acol})
+						b <<= 1
+					}
+				}
+			} else {
+				for x := 0; x < width; x += 8 {
+					b := cdat[x/8]
+					for x2 := 0; x2 < 8 && x+x2 < width; x2++ {
+						gray.SetGray(x+x2, y, color.Gray{(b >> 7) * 0xff})
+						b <<= 1
+					}
 				}
 			}
 		case cbG2:
-			for x := 0; x < width; x += 4 {
-				b := cdat[x/4]
-				for x2 := 0; x2 < 4 && x+x2 < width; x2++ {
-					gray.SetGray(x+x2, y, color.Gray{(b >> 6) * 0x55})
-					b <<= 2
+			if d.useTransparent {
+				ty := d.transparent[1]
+				for x := 0; x < width; x += 4 {
+					b := cdat[x/4]
+					for x2 := 0; x2 < 4 && x+x2 < width; x2++ {
+						ycol := (b >> 6) * 0x55
+						acol := uint8(0xff)
+						if ycol == ty {
+							acol = 0x00
+						}
+						nrgba.SetNRGBA(x+x2, y, color.NRGBA{ycol, ycol, ycol, acol})
+						b <<= 2
+					}
+				}
+			} else {
+				for x := 0; x < width; x += 4 {
+					b := cdat[x/4]
+					for x2 := 0; x2 < 4 && x+x2 < width; x2++ {
+						gray.SetGray(x+x2, y, color.Gray{(b >> 6) * 0x55})
+						b <<= 2
+					}
 				}
 			}
 		case cbG4:
-			for x := 0; x < width; x += 2 {
-				b := cdat[x/2]
-				for x2 := 0; x2 < 2 && x+x2 < width; x2++ {
-					gray.SetGray(x+x2, y, color.Gray{(b >> 4) * 0x11})
-					b <<= 4
+			if d.useTransparent {
+				ty := d.transparent[1]
+				for x := 0; x < width; x += 2 {
+					b := cdat[x/2]
+					for x2 := 0; x2 < 2 && x+x2 < width; x2++ {
+						ycol := (b >> 4) * 0x11
+						acol := uint8(0xff)
+						if ycol == ty {
+							acol = 0x00
+						}
+						nrgba.SetNRGBA(x+x2, y, color.NRGBA{ycol, ycol, ycol, acol})
+						b <<= 4
+					}
+				}
+			} else {
+				for x := 0; x < width; x += 2 {
+					b := cdat[x/2]
+					for x2 := 0; x2 < 2 && x+x2 < width; x2++ {
+						gray.SetGray(x+x2, y, color.Gray{(b >> 4) * 0x11})
+						b <<= 4
+					}
 				}
 			}
 		case cbG8:
@@ -515,16 +620,37 @@ func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image
 				nrgba.SetNRGBA(x, y, color.NRGBA{ycol, ycol, ycol, cdat[2*x+1]})
 			}
 		case cbTC8:
-			pix, i, j := rgba.Pix, pixOffset, 0
-			for x := 0; x < width; x++ {
-				pix[i+0] = cdat[j+0]
-				pix[i+1] = cdat[j+1]
-				pix[i+2] = cdat[j+2]
-				pix[i+3] = 0xff
-				i += 4
-				j += 3
+			if d.useTransparent {
+				pix, i, j := nrgba.Pix, pixOffset, 0
+				tr, tg, tb := d.transparent[1], d.transparent[3], d.transparent[5]
+				for x := 0; x < width; x++ {
+					r := cdat[j+0]
+					g := cdat[j+1]
+					b := cdat[j+2]
+					a := uint8(0xff)
+					if r == tr && g == tg && b == tb {
+						a = 0x00
+					}
+					pix[i+0] = r
+					pix[i+1] = g
+					pix[i+2] = b
+					pix[i+3] = a
+					i += 4
+					j += 3
+				}
+				pixOffset += nrgba.Stride
+			} else {
+				pix, i, j := rgba.Pix, pixOffset, 0
+				for x := 0; x < width; x++ {
+					pix[i+0] = cdat[j+0]
+					pix[i+1] = cdat[j+1]
+					pix[i+2] = cdat[j+2]
+					pix[i+3] = 0xff
+					i += 4
+					j += 3
+				}
+				pixOffset += rgba.Stride
 			}
-			pixOffset += rgba.Stride
 		case cbP1:
 			for x := 0; x < width; x += 8 {
 				b := cdat[x/8]
@@ -575,9 +701,21 @@ func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image
 			copy(nrgba.Pix[pixOffset:], cdat)
 			pixOffset += nrgba.Stride
 		case cbG16:
-			for x := 0; x < width; x++ {
-				ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
-				gray16.SetGray16(x, y, color.Gray16{ycol})
+			if d.useTransparent {
+				ty := uint16(d.transparent[0])<<8 | uint16(d.transparent[1])
+				for x := 0; x < width; x++ {
+					ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
+					acol := uint16(0xffff)
+					if ycol == ty {
+						acol = 0x0000
+					}
+					nrgba64.SetNRGBA64(x, y, color.NRGBA64{ycol, ycol, ycol, acol})
+				}
+			} else {
+				for x := 0; x < width; x++ {
+					ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
+					gray16.SetGray16(x, y, color.Gray16{ycol})
+				}
 			}
 		case cbGA16:
 			for x := 0; x < width; x++ {
@@ -586,11 +724,27 @@ func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image
 				nrgba64.SetNRGBA64(x, y, color.NRGBA64{ycol, ycol, ycol, acol})
 			}
 		case cbTC16:
-			for x := 0; x < width; x++ {
-				rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
-				gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
-				bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
-				rgba64.SetRGBA64(x, y, color.RGBA64{rcol, gcol, bcol, 0xffff})
+			if d.useTransparent {
+				tr := uint16(d.transparent[0])<<8 | uint16(d.transparent[1])
+				tg := uint16(d.transparent[2])<<8 | uint16(d.transparent[3])
+				tb := uint16(d.transparent[4])<<8 | uint16(d.transparent[5])
+				for x := 0; x < width; x++ {
+					rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
+					gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
+					bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
+					acol := uint16(0xffff)
+					if rcol == tr && gcol == tg && bcol == tb {
+						acol = 0x0000
+					}
+					nrgba64.SetNRGBA64(x, y, color.NRGBA64{rcol, gcol, bcol, acol})
+				}
+			} else {
+				for x := 0; x < width; x++ {
+					rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
+					gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
+					bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
+					rgba64.SetRGBA64(x, y, color.RGBA64{rcol, gcol, bcol, 0xffff})
+				}
 			}
 		case cbTCA16:
 			for x := 0; x < width; x++ {
@@ -709,7 +863,11 @@ func (d *decoder) parseChunk() error {
 		d.stage = dsSeenPLTE
 		return d.parsePLTE(length)
 	case "tRNS":
-		if d.stage != dsSeenPLTE {
+		if cbPaletted(d.cb) {
+			if d.stage != dsSeenPLTE {
+				return chunkOrderError
+			}
+		} else if d.stage != dsSeenIHDR {
 			return chunkOrderError
 		}
 		d.stage = dsSeentRNS
diff --git a/libgo/go/image/png/reader_test.go b/libgo/go/image/png/reader_test.go
index 0bc4203..b9e9f4d 100644
--- a/libgo/go/image/png/reader_test.go
+++ b/libgo/go/image/png/reader_test.go
@@ -39,6 +39,21 @@ var filenames = []string{
 	"basn4a16",
 	"basn6a08",
 	"basn6a16",
+	"ftbbn0g01",
+	"ftbbn0g02",
+	"ftbbn0g04",
+	"ftbbn2c16",
+	"ftbbn3p08",
+	"ftbgn2c16",
+	"ftbgn3p08",
+	"ftbrn2c08",
+	"ftbwn0g16",
+	"ftbwn3p08",
+	"ftbyn3p08",
+	"ftp0n0g08",
+	"ftp0n2c08",
+	"ftp0n3p08",
+	"ftp1n3p08",
 }
 
 var filenamesPaletted = []string{
@@ -64,6 +79,50 @@ func readPNG(filename string) (image.Image, error) {
 	return Decode(f)
 }
 
+// fakebKGDs maps from filenames to fake bKGD chunks for our approximation to
+// the sng command-line tool. Package png doesn't keep that metadata when
+// png.Decode returns an image.Image.
+var fakebKGDs = map[string]string{
+	"ftbbn0g01": "bKGD {gray: 0;}\n",
+	"ftbbn0g02": "bKGD {gray: 0;}\n",
+	"ftbbn0g04": "bKGD {gray: 0;}\n",
+	"ftbbn2c16": "bKGD {red: 0;  green: 0;  blue: 65535;}\n",
+	"ftbbn3p08": "bKGD {index: 245}\n",
+	"ftbgn2c16": "bKGD {red: 0;  green: 65535;  blue: 0;}\n",
+	"ftbgn3p08": "bKGD {index: 245}\n",
+	"ftbrn2c08": "bKGD {red: 255;  green: 0;  blue: 0;}\n",
+	"ftbwn0g16": "bKGD {gray: 65535;}\n",
+	"ftbwn3p08": "bKGD {index: 0}\n",
+	"ftbyn3p08": "bKGD {index: 245}\n",
+}
+
+// fakegAMAs maps from filenames to fake gAMA chunks for our approximation to
+// the sng command-line tool. Package png doesn't keep that metadata when
+// png.Decode returns an image.Image.
+var fakegAMAs = map[string]string{
+	"ftbbn0g01": "",
+	"ftbbn0g02": "gAMA {0.45455}\n",
+}
+
+// fakeIHDRUsings maps from filenames to fake IHDR "using" lines for our
+// approximation to the sng command-line tool. The PNG model is that
+// transparency (in the tRNS chunk) is separate to the color/grayscale/palette
+// color model (in the IHDR chunk). The Go model is that the concrete
+// image.Image type returned by png.Decode, such as image.RGBA (with all pixels
+// having 100% alpha) or image.NRGBA, encapsulates whether or not the image has
+// transparency. This map is a hack to work around the fact that the Go model
+// can't otherwise discriminate PNG's "IHDR says color (with no alpha) but tRNS
+// says alpha" and "IHDR says color with alpha".
+var fakeIHDRUsings = map[string]string{
+	"ftbbn0g01": "    using grayscale;\n",
+	"ftbbn0g02": "    using grayscale;\n",
+	"ftbbn0g04": "    using grayscale;\n",
+	"ftbbn2c16": "    using color;\n",
+	"ftbgn2c16": "    using color;\n",
+	"ftbrn2c08": "    using color;\n",
+	"ftbwn0g16": "    using grayscale;\n",
+}
+
 // An approximation of the sng command-line tool.
 func sng(w io.WriteCloser, filename string, png image.Image) {
 	defer w.Close()
@@ -95,25 +154,35 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
 	// Write the filename and IHDR.
 	io.WriteString(w, "#SNG: from "+filename+".png\nIHDR {\n")
 	fmt.Fprintf(w, "    width: %d; height: %d; bitdepth: %d;\n", bounds.Dx(), bounds.Dy(), bitdepth)
-	switch {
-	case cm == color.RGBAModel, cm == color.RGBA64Model:
-		io.WriteString(w, "    using color;\n")
-	case cm == color.NRGBAModel, cm == color.NRGBA64Model:
-		io.WriteString(w, "    using color alpha;\n")
-	case cm == color.GrayModel, cm == color.Gray16Model:
-		io.WriteString(w, "    using grayscale;\n")
-	case cpm != nil:
-		io.WriteString(w, "    using color palette;\n")
-	default:
-		io.WriteString(w, "unknown PNG decoder color model\n")
+	if s, ok := fakeIHDRUsings[filename]; ok {
+		io.WriteString(w, s)
+	} else {
+		switch {
+		case cm == color.RGBAModel, cm == color.RGBA64Model:
+			io.WriteString(w, "    using color;\n")
+		case cm == color.NRGBAModel, cm == color.NRGBA64Model:
+			io.WriteString(w, "    using color alpha;\n")
+		case cm == color.GrayModel, cm == color.Gray16Model:
+			io.WriteString(w, "    using grayscale;\n")
+		case cpm != nil:
+			io.WriteString(w, "    using color palette;\n")
+		default:
+			io.WriteString(w, "unknown PNG decoder color model\n")
+		}
 	}
 	io.WriteString(w, "}\n")
 
-	// We fake a gAMA output. The test files have a gAMA chunk but the go PNG parser ignores it
-	// (the PNG spec section 11.3 says "Ancillary chunks may be ignored by a decoder").
-	io.WriteString(w, "gAMA {1.0000}\n")
+	// We fake a gAMA chunk. The test files have a gAMA chunk but the go PNG
+	// parser ignores it (the PNG spec section 11.3 says "Ancillary chunks may
+	// be ignored by a decoder").
+	if s, ok := fakegAMAs[filename]; ok {
+		io.WriteString(w, s)
+	} else {
+		io.WriteString(w, "gAMA {1.0000}\n")
+	}
 
 	// Write the PLTE and tRNS (if applicable).
+	useTransparent := false
 	if cpm != nil {
 		lastAlpha := -1
 		io.WriteString(w, "PLTE {\n")
@@ -133,6 +202,9 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
 			fmt.Fprintf(w, "    (%3d,%3d,%3d)     # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
 		}
 		io.WriteString(w, "}\n")
+		if s, ok := fakebKGDs[filename]; ok {
+			io.WriteString(w, s)
+		}
 		if lastAlpha != -1 {
 			io.WriteString(w, "tRNS {\n")
 			for i := 0; i <= lastAlpha; i++ {
@@ -142,6 +214,42 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
 			}
 			io.WriteString(w, "}\n")
 		}
+	} else if strings.HasPrefix(filename, "ft") {
+		if s, ok := fakebKGDs[filename]; ok {
+			io.WriteString(w, s)
+		}
+		// We fake a tRNS chunk. The test files' grayscale and truecolor
+		// transparent images all have their top left corner transparent.
+		switch c := png.At(0, 0).(type) {
+		case color.NRGBA:
+			if c.A == 0 {
+				useTransparent = true
+				io.WriteString(w, "tRNS {\n")
+				switch filename {
+				case "ftbbn0g01", "ftbbn0g02", "ftbbn0g04":
+					// The standard image package doesn't have a "gray with
+					// alpha" type. Instead, we use an image.NRGBA.
+					fmt.Fprintf(w, "    gray: %d;\n", c.R)
+				default:
+					fmt.Fprintf(w, "    red: %d; green: %d; blue: %d;\n", c.R, c.G, c.B)
+				}
+				io.WriteString(w, "}\n")
+			}
+		case color.NRGBA64:
+			if c.A == 0 {
+				useTransparent = true
+				io.WriteString(w, "tRNS {\n")
+				switch filename {
+				case "ftbwn0g16":
+					// The standard image package doesn't have a "gray16 with
+					// alpha" type. Instead, we use an image.NRGBA64.
+					fmt.Fprintf(w, "    gray: %d;\n", c.R)
+				default:
+					fmt.Fprintf(w, "    red: %d; green: %d; blue: %d;\n", c.R, c.G, c.B)
+				}
+				io.WriteString(w, "}\n")
+			}
+		}
 	}
 
 	// Write the IMAGE.
@@ -171,12 +279,30 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
 		case cm == color.NRGBAModel:
 			for x := bounds.Min.X; x < bounds.Max.X; x++ {
 				nrgba := png.At(x, y).(color.NRGBA)
-				fmt.Fprintf(w, "%02x%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B, nrgba.A)
+				switch filename {
+				case "ftbbn0g01", "ftbbn0g02", "ftbbn0g04":
+					fmt.Fprintf(w, "%02x", nrgba.R)
+				default:
+					if useTransparent {
+						fmt.Fprintf(w, "%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B)
+					} else {
+						fmt.Fprintf(w, "%02x%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B, nrgba.A)
+					}
+				}
 			}
 		case cm == color.NRGBA64Model:
 			for x := bounds.Min.X; x < bounds.Max.X; x++ {
 				nrgba64 := png.At(x, y).(color.NRGBA64)
-				fmt.Fprintf(w, "%04x%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B, nrgba64.A)
+				switch filename {
+				case "ftbwn0g16":
+					fmt.Fprintf(w, "%04x ", nrgba64.R)
+				default:
+					if useTransparent {
+						fmt.Fprintf(w, "%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B)
+					} else {
+						fmt.Fprintf(w, "%04x%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B, nrgba64.A)
+					}
+				}
 			}
 		case cpm != nil:
 			var b, c int
@@ -256,8 +382,23 @@ func TestReader(t *testing.T) {
 			}
 			ps := pb.Text()
 			ss := sb.Text()
+
+			// Newer versions of the sng command line tool append an optional
+			// color name to the RGB tuple. For example:
+			//	# rgb = (0xff,0xff,0xff) grey100
+			//	# rgb = (0x00,0x00,0xff) blue1
+			// instead of the older version's plainer:
+			//	# rgb = (0xff,0xff,0xff)
+			//	# rgb = (0x00,0x00,0xff)
+			// We strip any such name.
+			if strings.Contains(ss, "# rgb = (") && !strings.HasSuffix(ss, ")") {
+				if i := strings.LastIndex(ss, ") "); i >= 0 {
+					ss = ss[:i+1]
+				}
+			}
+
 			if ps != ss {
-				t.Errorf("%s: Mismatch\n%sversus\n%s\n", fn, ps, ss)
+				t.Errorf("%s: Mismatch\n%s\nversus\n%s\n", fn, ps, ss)
 				break
 			}
 		}
diff --git a/libgo/go/image/png/testdata/pngsuite/README b/libgo/go/image/png/testdata/pngsuite/README
index c0f78bd..01d1d89 100644
--- a/libgo/go/image/png/testdata/pngsuite/README
+++ b/libgo/go/image/png/testdata/pngsuite/README
@@ -1,21 +1,20 @@
 The *.png and README.original files in this directory are copied from
-libpng.org, specifically contrib/pngsuite/* in libpng-1.2.40.tar.gz.
+libpng.org, specifically contrib/pngsuite/* in libpng 1.6.26.
+
 README.original gives the following license for those files:
 
 	Permission to use, copy, and distribute these images for any purpose
 	and without fee is hereby granted.
 
-
-The files basn0g01-30.png, basn0g02-29.png and basn0g04-31.png are in fact
-not part of pngsuite but were created from files in pngsuite. Their non-power-
-of-two sizes makes them useful for testing bit-depths smaller than a byte.
+The files basn0g01-30.png, basn0g02-29.png and basn0g04-31.png are in fact not
+part of pngsuite but were created from files in pngsuite. Their non-power-of-2
+sizes makes them useful for testing bit-depths smaller than a byte.
 
 basn3a08.png was generated from basn6a08.png using the pngnq tool, which
 converted it to the 8-bit paletted image with alpha values in tRNS chunk.
 
-The *.sng files in this directory were generated from the *.png files
-by the sng command-line tool and some hand editing. The files
-basn0g0{1,2,4}.sng were actually generated by first converting the PNG
-to a bitdepth of 8 and then running sng on them. basn4a08.sng was generated
-by from a 16-bit rgba version of basn4a08.png rather than the original
-gray + alpha.
+The *.sng files in this directory were generated from the *.png files by the
+sng command-line tool and some hand editing. The files basn0g0{1,2,4}.sng and
+ftbbn0g0{1,2,4}.sng were actually generated by first converting the PNG to a
+bitdepth of 8 and then running sng on them. basn4a08.sng was generated from a
+16-bit rgba version of basn4a08.png rather than the original gray + alpha.
diff --git a/libgo/go/image/png/writer.go b/libgo/go/image/png/writer.go
index df23270..dd87d81 100644
--- a/libgo/go/image/png/writer.go
+++ b/libgo/go/image/png/writer.go
@@ -420,8 +420,11 @@ func writeImage(w io.Writer, m image.Image, cb int, level int) error {
 		}
 
 		// Apply the filter.
+		// Skip filter for NoCompression and paletted images (cbP8) as
+		// "filters are rarely useful on palette images" and will result
+		// in larger files (see http://www.libpng.org/pub/png/book/chapter09.html).
 		f := ftNone
-		if level != zlib.NoCompression {
+		if level != zlib.NoCompression && cb != cbP8 {
 			f = filter(&cr, pr, bpp)
 		}