libgo: Update to current sources.

From-SVN: r192704

6 files changed, 337 insertions, 93 deletions

diff --git a/libgo/go/image/png/paeth.go b/libgo/go/image/png/paeth.go
new file mode 100644
index 0000000..37978aa
--- /dev/null
+++ b/libgo/go/image/png/paeth.go
@@ -0,0 +1,70 @@
+// 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.
+
+package png
+
+// paeth implements the Paeth filter function, as per the PNG specification.
+func paeth(a, b, c uint8) uint8 {
+	// This is an optimized version of the sample code in the PNG spec.
+	// For example, the sample code starts with:
+	//	p := int(a) + int(b) - int(c)
+	//	pa := abs(p - int(a))
+	// but the optimized form uses fewer arithmetic operations:
+	//	pa := int(b) - int(c)
+	//	pa = abs(pa)
+	pc := int(c)
+	pa := int(b) - pc
+	pb := int(a) - pc
+	pc = pa + pb
+	if pa < 0 {
+		pa = -pa
+	}
+	if pb < 0 {
+		pb = -pb
+	}
+	if pc < 0 {
+		pc = -pc
+	}
+	if pa <= pb && pa <= pc {
+		return a
+	} else if pb <= pc {
+		return b
+	}
+	return c
+}
+
+// filterPaeth applies the Paeth filter to the cdat slice.
+// cdat is the current row's data, pdat is the previous row's data.
+func filterPaeth(cdat, pdat []byte, bytesPerPixel int) {
+	var a, b, c, pa, pb, pc int
+	for i := 0; i < bytesPerPixel; i++ {
+		a, c = 0, 0
+		for j := i; j < len(cdat); j += bytesPerPixel {
+			b = int(pdat[j])
+			pa = b - c
+			pb = a - c
+			pc = pa + pb
+			if pa < 0 {
+				pa = -pa
+			}
+			if pb < 0 {
+				pb = -pb
+			}
+			if pc < 0 {
+				pc = -pc
+			}
+			if pa <= pb && pa <= pc {
+				// No-op.
+			} else if pb <= pc {
+				a = b
+			} else {
+				a = c
+			}
+			a += int(cdat[j])
+			a &= 0xff
+			cdat[j] = uint8(a)
+			c = b
+		}
+	}
+}
diff --git a/libgo/go/image/png/paeth_test.go b/libgo/go/image/png/paeth_test.go
new file mode 100644
index 0000000..bb08486
--- /dev/null
+++ b/libgo/go/image/png/paeth_test.go
@@ -0,0 +1,91 @@
+// 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.
+
+package png
+
+import (
+	"bytes"
+	"math/rand"
+	"testing"
+)
+
+func abs(x int) int {
+	if x < 0 {
+		return -x
+	}
+	return x
+}
+
+// slowPaeth is a slow but simple implementation of the Paeth function.
+// It is a straight port of the sample code in the PNG spec, section 9.4.
+func slowPaeth(a, b, c uint8) uint8 {
+	p := int(a) + int(b) - int(c)
+	pa := abs(p - int(a))
+	pb := abs(p - int(b))
+	pc := abs(p - int(c))
+	if pa <= pb && pa <= pc {
+		return a
+	} else if pb <= pc {
+		return b
+	}
+	return c
+}
+
+// slowFilterPaeth is a slow but simple implementation of func filterPaeth.
+func slowFilterPaeth(cdat, pdat []byte, bytesPerPixel int) {
+	for i := 0; i < bytesPerPixel; i++ {
+		cdat[i] += paeth(0, pdat[i], 0)
+	}
+	for i := bytesPerPixel; i < len(cdat); i++ {
+		cdat[i] += paeth(cdat[i-bytesPerPixel], pdat[i], pdat[i-bytesPerPixel])
+	}
+}
+
+func TestPaeth(t *testing.T) {
+	for a := 0; a < 256; a += 15 {
+		for b := 0; b < 256; b += 15 {
+			for c := 0; c < 256; c += 15 {
+				got := paeth(uint8(a), uint8(b), uint8(c))
+				want := slowPaeth(uint8(a), uint8(b), uint8(c))
+				if got != want {
+					t.Errorf("a, b, c = %d, %d, %d: got %d, want %d", a, b, c, got, want)
+				}
+			}
+		}
+	}
+}
+
+func BenchmarkPaeth(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		paeth(uint8(i>>16), uint8(i>>8), uint8(i))
+	}
+}
+
+func TestPaethDecode(t *testing.T) {
+	pdat0 := make([]byte, 32)
+	pdat1 := make([]byte, 32)
+	pdat2 := make([]byte, 32)
+	cdat0 := make([]byte, 32)
+	cdat1 := make([]byte, 32)
+	cdat2 := make([]byte, 32)
+	r := rand.New(rand.NewSource(1))
+	for bytesPerPixel := 1; bytesPerPixel <= 8; bytesPerPixel++ {
+		for i := 0; i < 100; i++ {
+			for j := range pdat0 {
+				pdat0[j] = uint8(r.Uint32())
+				cdat0[j] = uint8(r.Uint32())
+			}
+			copy(pdat1, pdat0)
+			copy(pdat2, pdat0)
+			copy(cdat1, cdat0)
+			copy(cdat2, cdat0)
+			filterPaeth(cdat1, pdat1, bytesPerPixel)
+			slowFilterPaeth(cdat2, pdat2, bytesPerPixel)
+			if !bytes.Equal(cdat1, cdat2) {
+				t.Errorf("bytesPerPixel: %d\npdat0: % x\ncdat0: % x\ngot:   % x\nwant:  % x", bytesPerPixel, pdat0, cdat0, cdat1, cdat2)
+				break
+			}
+		}
+	}
+}
diff --git a/libgo/go/image/png/reader.go b/libgo/go/image/png/reader.go
index fe07d60..b3901b2 100644
--- a/libgo/go/image/png/reader.go
+++ b/libgo/go/image/png/reader.go
@@ -98,13 +98,6 @@ type UnsupportedError string
 
 func (e UnsupportedError) Error() string { return "png: unsupported feature: " + string(e) }
 
-func abs(x int) int {
-	if x < 0 {
-		return -x
-	}
-	return x
-}
-
 func min(a, b int) int {
 	if a < b {
 		return a
@@ -233,7 +226,7 @@ func (d *decoder) parsetRNS(length uint32) error {
 		}
 		for i := 0; i < n; i++ {
 			rgba := d.palette[i].(color.RGBA)
-			d.palette[i] = color.RGBA{rgba.R, rgba.G, rgba.B, d.tmp[i]}
+			d.palette[i] = color.NRGBA{rgba.R, rgba.G, rgba.B, d.tmp[i]}
 		}
 	case cbGA8, cbGA16, cbTCA8, cbTCA16:
 		return FormatError("tRNS, color type mismatch")
@@ -241,20 +234,6 @@ func (d *decoder) parsetRNS(length uint32) error {
 	return d.verifyChecksum()
 }
 
-// The Paeth filter function, as per the PNG specification.
-func paeth(a, b, c uint8) uint8 {
-	p := int(a) + int(b) - int(c)
-	pa := abs(p - int(a))
-	pb := abs(p - int(b))
-	pc := abs(p - int(c))
-	if pa <= pb && pa <= pc {
-		return a
-	} else if pb <= pc {
-		return b
-	}
-	return c
-}
-
 // Read presents one or more IDAT chunks as one continuous stream (minus the
 // intermediate chunk headers and footers). If the PNG data looked like:
 //   ... len0 IDAT xxx crc0 len1 IDAT yy crc1 len2 IEND crc2
@@ -301,6 +280,7 @@ func (d *decoder) decode() (image.Image, error) {
 	defer r.Close()
 	bitsPerPixel := 0
 	maxPalette := uint8(0)
+	pixOffset := 0
 	var (
 		gray     *image.Gray
 		rgba     *image.RGBA
@@ -375,8 +355,8 @@ func (d *decoder) decode() (image.Image, error) {
 				cdat[i] += cdat[i-bytesPerPixel]
 			}
 		case ftUp:
-			for i := 0; i < len(cdat); i++ {
-				cdat[i] += pdat[i]
+			for i, p := range pdat {
+				cdat[i] += p
 			}
 		case ftAverage:
 			for i := 0; i < bytesPerPixel; i++ {
@@ -386,12 +366,7 @@ func (d *decoder) decode() (image.Image, error) {
 				cdat[i] += uint8((int(cdat[i-bytesPerPixel]) + int(pdat[i])) / 2)
 			}
 		case ftPaeth:
-			for i := 0; i < bytesPerPixel; i++ {
-				cdat[i] += paeth(0, pdat[i], 0)
-			}
-			for i := bytesPerPixel; i < len(cdat); i++ {
-				cdat[i] += paeth(cdat[i-bytesPerPixel], pdat[i], pdat[i-bytesPerPixel])
-			}
+			filterPaeth(cdat, pdat, bytesPerPixel)
 		default:
 			return nil, FormatError("bad filter type")
 		}
@@ -423,18 +398,24 @@ func (d *decoder) decode() (image.Image, error) {
 				}
 			}
 		case cbG8:
-			for x := 0; x < d.width; x++ {
-				gray.SetGray(x, y, color.Gray{cdat[x]})
-			}
+			copy(gray.Pix[pixOffset:], cdat)
+			pixOffset += gray.Stride
 		case cbGA8:
 			for x := 0; x < d.width; x++ {
 				ycol := cdat[2*x+0]
 				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 < d.width; x++ {
-				rgba.SetRGBA(x, y, color.RGBA{cdat[3*x+0], cdat[3*x+1], cdat[3*x+2], 0xff})
+				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
 		case cbP1:
 			for x := 0; x < d.width; x += 8 {
 				b := cdat[x/8]
@@ -472,16 +453,18 @@ func (d *decoder) decode() (image.Image, error) {
 				}
 			}
 		case cbP8:
-			for x := 0; x < d.width; x++ {
-				if cdat[x] > maxPalette {
-					return nil, FormatError("palette index out of range")
+			if maxPalette != 255 {
+				for x := 0; x < d.width; x++ {
+					if cdat[x] > maxPalette {
+						return nil, FormatError("palette index out of range")
+					}
 				}
-				paletted.SetColorIndex(x, y, cdat[x])
 			}
+			copy(paletted.Pix[pixOffset:], cdat)
+			pixOffset += paletted.Stride
 		case cbTCA8:
-			for x := 0; x < d.width; x++ {
-				nrgba.SetNRGBA(x, y, color.NRGBA{cdat[4*x+0], cdat[4*x+1], cdat[4*x+2], cdat[4*x+3]})
-			}
+			copy(nrgba.Pix[pixOffset:], cdat)
+			pixOffset += nrgba.Stride
 		case cbG16:
 			for x := 0; x < d.width; x++ {
 				ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
diff --git a/libgo/go/image/png/reader_test.go b/libgo/go/image/png/reader_test.go
index 24c4ea4..8223f52 100644
--- a/libgo/go/image/png/reader_test.go
+++ b/libgo/go/image/png/reader_test.go
@@ -10,6 +10,7 @@ import (
 	"image"
 	"image/color"
 	"io"
+	"io/ioutil"
 	"os"
 	"strings"
 	"testing"
@@ -106,13 +107,18 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
 		lastAlpha := -1
 		io.WriteString(w, "PLTE {\n")
 		for i, c := range cpm {
-			r, g, b, a := c.RGBA()
-			if a != 0xffff {
+			var r, g, b, a uint8
+			switch c := c.(type) {
+			case color.RGBA:
+				r, g, b, a = c.R, c.G, c.B, 0xff
+			case color.NRGBA:
+				r, g, b, a = c.R, c.G, c.B, c.A
+			default:
+				panic("unknown palette color type")
+			}
+			if a != 0xff {
 				lastAlpha = i
 			}
-			r >>= 8
-			g >>= 8
-			b >>= 8
 			fmt.Fprintf(w, "    (%3d,%3d,%3d)     # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
 		}
 		io.WriteString(w, "}\n")
@@ -267,3 +273,41 @@ func TestReaderError(t *testing.T) {
 		}
 	}
 }
+
+func benchmarkDecode(b *testing.B, filename string, bytesPerPixel int) {
+	b.StopTimer()
+	data, err := ioutil.ReadFile(filename)
+	if err != nil {
+		b.Fatal(err)
+	}
+	s := string(data)
+	cfg, err := DecodeConfig(strings.NewReader(s))
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.SetBytes(int64(cfg.Width * cfg.Height * bytesPerPixel))
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		Decode(strings.NewReader(s))
+	}
+}
+
+func BenchmarkDecodeGray(b *testing.B) {
+	benchmarkDecode(b, "testdata/benchGray.png", 1)
+}
+
+func BenchmarkDecodeNRGBAGradient(b *testing.B) {
+	benchmarkDecode(b, "testdata/benchNRGBA-gradient.png", 4)
+}
+
+func BenchmarkDecodeNRGBAOpaque(b *testing.B) {
+	benchmarkDecode(b, "testdata/benchNRGBA-opaque.png", 4)
+}
+
+func BenchmarkDecodePaletted(b *testing.B) {
+	benchmarkDecode(b, "testdata/benchPaletted.png", 1)
+}
+
+func BenchmarkDecodeRGB(b *testing.B) {
+	benchmarkDecode(b, "testdata/benchRGB.png", 4)
+}
diff --git a/libgo/go/image/png/writer.go b/libgo/go/image/png/writer.go
index 57c0379..093d471 100644
--- a/libgo/go/image/png/writer.go
+++ b/libgo/go/image/png/writer.go
@@ -21,7 +21,7 @@ type encoder struct {
 	err    error
 	header [8]byte
 	footer [4]byte
-	tmp    [3 * 256]byte
+	tmp    [4 * 256]byte
 }
 
 // Big-endian.
@@ -70,7 +70,7 @@ func (e *encoder) writeChunk(b []byte, name string) {
 		e.err = UnsupportedError(name + " chunk is too large: " + strconv.Itoa(len(b)))
 		return
 	}
-	writeUint32(e.header[0:4], n)
+	writeUint32(e.header[:4], n)
 	e.header[4] = name[0]
 	e.header[5] = name[1]
 	e.header[6] = name[2]
@@ -78,9 +78,9 @@ func (e *encoder) writeChunk(b []byte, name string) {
 	crc := crc32.NewIEEE()
 	crc.Write(e.header[4:8])
 	crc.Write(b)
-	writeUint32(e.footer[0:4], crc.Sum32())
+	writeUint32(e.footer[:4], crc.Sum32())
 
-	_, e.err = e.w.Write(e.header[0:8])
+	_, e.err = e.w.Write(e.header[:8])
 	if e.err != nil {
 		return
 	}
@@ -88,7 +88,7 @@ func (e *encoder) writeChunk(b []byte, name string) {
 	if e.err != nil {
 		return
 	}
-	_, e.err = e.w.Write(e.footer[0:4])
+	_, e.err = e.w.Write(e.footer[:4])
 }
 
 func (e *encoder) writeIHDR() {
@@ -122,36 +122,29 @@ func (e *encoder) writeIHDR() {
 	e.tmp[10] = 0 // default compression method
 	e.tmp[11] = 0 // default filter method
 	e.tmp[12] = 0 // non-interlaced
-	e.writeChunk(e.tmp[0:13], "IHDR")
+	e.writeChunk(e.tmp[:13], "IHDR")
 }
 
-func (e *encoder) writePLTE(p color.Palette) {
+func (e *encoder) writePLTEAndTRNS(p color.Palette) {
 	if len(p) < 1 || len(p) > 256 {
 		e.err = FormatError("bad palette length: " + strconv.Itoa(len(p)))
 		return
 	}
-	for i, c := range p {
-		r, g, b, _ := c.RGBA()
-		e.tmp[3*i+0] = uint8(r >> 8)
-		e.tmp[3*i+1] = uint8(g >> 8)
-		e.tmp[3*i+2] = uint8(b >> 8)
-	}
-	e.writeChunk(e.tmp[0:3*len(p)], "PLTE")
-}
-
-func (e *encoder) maybeWritetRNS(p color.Palette) {
 	last := -1
 	for i, c := range p {
-		_, _, _, a := c.RGBA()
-		if a != 0xffff {
+		c1 := color.NRGBAModel.Convert(c).(color.NRGBA)
+		e.tmp[3*i+0] = c1.R
+		e.tmp[3*i+1] = c1.G
+		e.tmp[3*i+2] = c1.B
+		if c1.A != 0xff {
 			last = i
 		}
-		e.tmp[i] = uint8(a >> 8)
+		e.tmp[3*256+i] = c1.A
 	}
-	if last == -1 {
-		return
+	e.writeChunk(e.tmp[:3*len(p)], "PLTE")
+	if last != -1 {
+		e.writeChunk(e.tmp[3*256:3*256+1+last], "tRNS")
 	}
-	e.writeChunk(e.tmp[:last+1], "tRNS")
 }
 
 // An encoder is an io.Writer that satisfies writes by writing PNG IDAT chunks,
@@ -297,26 +290,42 @@ func writeImage(w io.Writer, m image.Image, cb int) error {
 	}
 	pr := make([]uint8, 1+bpp*b.Dx())
 
+	gray, _ := m.(*image.Gray)
+	rgba, _ := m.(*image.RGBA)
+	paletted, _ := m.(*image.Paletted)
+	nrgba, _ := m.(*image.NRGBA)
+
 	for y := b.Min.Y; y < b.Max.Y; y++ {
 		// Convert from colors to bytes.
 		i := 1
 		switch cb {
 		case cbG8:
-			for x := b.Min.X; x < b.Max.X; x++ {
-				c := color.GrayModel.Convert(m.At(x, y)).(color.Gray)
-				cr[0][i] = c.Y
-				i++
+			if gray != nil {
+				offset := (y - b.Min.Y) * gray.Stride
+				copy(cr[0][1:], gray.Pix[offset:offset+b.Dx()])
+			} else {
+				for x := b.Min.X; x < b.Max.X; x++ {
+					c := color.GrayModel.Convert(m.At(x, y)).(color.Gray)
+					cr[0][i] = c.Y
+					i++
+				}
 			}
 		case cbTC8:
 			// We have previously verified that the alpha value is fully opaque.
 			cr0 := cr[0]
-			if rgba, _ := m.(*image.RGBA); rgba != nil {
-				j0 := (y - b.Min.Y) * rgba.Stride
+			stride, pix := 0, []byte(nil)
+			if rgba != nil {
+				stride, pix = rgba.Stride, rgba.Pix
+			} else if nrgba != nil {
+				stride, pix = nrgba.Stride, nrgba.Pix
+			}
+			if stride != 0 {
+				j0 := (y - b.Min.Y) * stride
 				j1 := j0 + b.Dx()*4
 				for j := j0; j < j1; j += 4 {
-					cr0[i+0] = rgba.Pix[j+0]
-					cr0[i+1] = rgba.Pix[j+1]
-					cr0[i+2] = rgba.Pix[j+2]
+					cr0[i+0] = pix[j+0]
+					cr0[i+1] = pix[j+1]
+					cr0[i+2] = pix[j+2]
 					i += 3
 				}
 			} else {
@@ -329,9 +338,9 @@ func writeImage(w io.Writer, m image.Image, cb int) error {
 				}
 			}
 		case cbP8:
-			if p, _ := m.(*image.Paletted); p != nil {
-				offset := (y - b.Min.Y) * p.Stride
-				copy(cr[0][1:], p.Pix[offset:offset+b.Dx()])
+			if paletted != nil {
+				offset := (y - b.Min.Y) * paletted.Stride
+				copy(cr[0][1:], paletted.Pix[offset:offset+b.Dx()])
 			} else {
 				pi := m.(image.PalettedImage)
 				for x := b.Min.X; x < b.Max.X; x++ {
@@ -340,14 +349,19 @@ func writeImage(w io.Writer, m image.Image, cb int) error {
 				}
 			}
 		case cbTCA8:
-			// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
-			for x := b.Min.X; x < b.Max.X; x++ {
-				c := color.NRGBAModel.Convert(m.At(x, y)).(color.NRGBA)
-				cr[0][i+0] = c.R
-				cr[0][i+1] = c.G
-				cr[0][i+2] = c.B
-				cr[0][i+3] = c.A
-				i += 4
+			if nrgba != nil {
+				offset := (y - b.Min.Y) * nrgba.Stride
+				copy(cr[0][1:], nrgba.Pix[offset:offset+b.Dx()*4])
+			} else {
+				// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
+				for x := b.Min.X; x < b.Max.X; x++ {
+					c := color.NRGBAModel.Convert(m.At(x, y)).(color.NRGBA)
+					cr[0][i+0] = c.R
+					cr[0][i+1] = c.G
+					cr[0][i+2] = c.B
+					cr[0][i+3] = c.A
+					i += 4
+				}
 			}
 		case cbG16:
 			for x := b.Min.X; x < b.Max.X; x++ {
@@ -412,7 +426,7 @@ func (e *encoder) writeIDATs() {
 	e.err = bw.Flush()
 }
 
-func (e *encoder) writeIEND() { e.writeChunk(e.tmp[0:0], "IEND") }
+func (e *encoder) writeIEND() { e.writeChunk(nil, "IEND") }
 
 // Encode writes the Image m to w in PNG format. Any Image may be encoded, but
 // images that are not image.NRGBA might be encoded lossily.
@@ -460,8 +474,7 @@ func Encode(w io.Writer, m image.Image) error {
 	_, e.err = io.WriteString(w, pngHeader)
 	e.writeIHDR()
 	if pal != nil {
-		e.writePLTE(pal)
-		e.maybeWritetRNS(pal)
+		e.writePLTEAndTRNS(pal)
 	}
 	e.writeIDATs()
 	e.writeIEND()
diff --git a/libgo/go/image/png/writer_test.go b/libgo/go/image/png/writer_test.go
index 644c4fb..3116fc9 100644
--- a/libgo/go/image/png/writer_test.go
+++ b/libgo/go/image/png/writer_test.go
@@ -101,6 +101,49 @@ func TestSubImage(t *testing.T) {
 	}
 }
 
+func BenchmarkEncodeGray(b *testing.B) {
+	b.StopTimer()
+	img := image.NewGray(image.Rect(0, 0, 640, 480))
+	b.SetBytes(640 * 480 * 1)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		Encode(ioutil.Discard, img)
+	}
+}
+
+func BenchmarkEncodeNRGBOpaque(b *testing.B) {
+	b.StopTimer()
+	img := image.NewNRGBA(image.Rect(0, 0, 640, 480))
+	// Set all pixels to 0xFF alpha to force opaque mode.
+	bo := img.Bounds()
+	for y := bo.Min.Y; y < bo.Max.Y; y++ {
+		for x := bo.Min.X; x < bo.Max.X; x++ {
+			img.Set(x, y, color.NRGBA{0, 0, 0, 255})
+		}
+	}
+	if !img.Opaque() {
+		b.Fatal("expected image to be opaque")
+	}
+	b.SetBytes(640 * 480 * 4)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		Encode(ioutil.Discard, img)
+	}
+}
+
+func BenchmarkEncodeNRGBA(b *testing.B) {
+	b.StopTimer()
+	img := image.NewNRGBA(image.Rect(0, 0, 640, 480))
+	if img.Opaque() {
+		b.Fatal("expected image not to be opaque")
+	}
+	b.SetBytes(640 * 480 * 4)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		Encode(ioutil.Discard, img)
+	}
+}
+
 func BenchmarkEncodePaletted(b *testing.B) {
 	b.StopTimer()
 	img := image.NewPaletted(image.Rect(0, 0, 640, 480), color.Palette{
@@ -138,7 +181,7 @@ func BenchmarkEncodeRGBA(b *testing.B) {
 	b.StopTimer()
 	img := image.NewRGBA(image.Rect(0, 0, 640, 480))
 	if img.Opaque() {
-		b.Fatal("expected image to not be opaque")
+		b.Fatal("expected image not to be opaque")
 	}
 	b.SetBytes(640 * 480 * 4)
 	b.StartTimer()