libgo: update to go1.9

[official-gcc.git] / libgo / go / image / png / reader_test.go

// Copyright 2009 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 (
        "bufio"
        "bytes"
        "fmt"
        "image"
        "image/color"
        "io"
        "io/ioutil"
        "os"
        "reflect"
        "strings"
        "testing"
)

var filenames = []string{
        "basn0g01",
        "basn0g01-30",
        "basn0g02",
        "basn0g02-29",
        "basn0g04",
        "basn0g04-31",
        "basn0g08",
        "basn0g16",
        "basn2c08",
        "basn2c16",
        "basn3p01",
        "basn3p02",
        "basn3p04",
        "basn3p04-31i",
        "basn3p08",
        "basn3p08-trns",
        "basn4a08",
        "basn4a16",
        "basn6a08",
        "basn6a16",
        "ftbbn0g01",
        "ftbbn0g02",
        "ftbbn0g04",
        "ftbbn2c16",
        "ftbbn3p08",
        "ftbgn2c16",
        "ftbgn3p08",
        "ftbrn2c08",
        "ftbwn0g16",
        "ftbwn3p08",
        "ftbyn3p08",
        "ftp0n0g08",
        "ftp0n2c08",
        "ftp0n3p08",
        "ftp1n3p08",
}

var filenamesPaletted = []string{
        "basn3p01",
        "basn3p02",
        "basn3p04",
        "basn3p08",
        "basn3p08-trns",
}

var filenamesShort = []string{
        "basn0g01",
        "basn0g04-31",
        "basn6a16",
}

func readPNG(filename string) (image.Image, error) {
        f, err := os.Open(filename)
        if err != nil {
                return nil, err
        }
        defer f.Close()
        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()
        bounds := png.Bounds()
        cm := png.ColorModel()
        var bitdepth int
        switch cm {
        case color.RGBAModel, color.NRGBAModel, color.AlphaModel, color.GrayModel:
                bitdepth = 8
        default:
                bitdepth = 16
        }
        cpm, _ := cm.(color.Palette)
        var paletted *image.Paletted
        if cpm != nil {
                switch {
                case len(cpm) <= 2:
                        bitdepth = 1
                case len(cpm) <= 4:
                        bitdepth = 2
                case len(cpm) <= 16:
                        bitdepth = 4
                default:
                        bitdepth = 8
                }
                paletted = png.(*image.Paletted)
        }

        // 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)
        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 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")
                for i, c := range cpm {
                        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
                        }
                        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++ {
                                _, _, _, a := cpm[i].RGBA()
                                a >>= 8
                                fmt.Fprintf(w, " %d", a)
                        }
                        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.
        io.WriteString(w, "IMAGE {\n    pixels hex\n")
        for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
                switch {
                case cm == color.GrayModel:
                        for x := bounds.Min.X; x < bounds.Max.X; x++ {
                                gray := png.At(x, y).(color.Gray)
                                fmt.Fprintf(w, "%02x", gray.Y)
                        }
                case cm == color.Gray16Model:
                        for x := bounds.Min.X; x < bounds.Max.X; x++ {
                                gray16 := png.At(x, y).(color.Gray16)
                                fmt.Fprintf(w, "%04x ", gray16.Y)
                        }
                case cm == color.RGBAModel:
                        for x := bounds.Min.X; x < bounds.Max.X; x++ {
                                rgba := png.At(x, y).(color.RGBA)
                                fmt.Fprintf(w, "%02x%02x%02x ", rgba.R, rgba.G, rgba.B)
                        }
                case cm == color.RGBA64Model:
                        for x := bounds.Min.X; x < bounds.Max.X; x++ {
                                rgba64 := png.At(x, y).(color.RGBA64)
                                fmt.Fprintf(w, "%04x%04x%04x ", rgba64.R, rgba64.G, rgba64.B)
                        }
                case cm == color.NRGBAModel:
                        for x := bounds.Min.X; x < bounds.Max.X; x++ {
                                nrgba := png.At(x, y).(color.NRGBA)
                                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)
                                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
                        for x := bounds.Min.X; x < bounds.Max.X; x++ {
                                b = b<<uint(bitdepth) | int(paletted.ColorIndexAt(x, y))
                                c++
                                if c == 8/bitdepth {
                                        fmt.Fprintf(w, "%02x", b)
                                        b = 0
                                        c = 0
                                }
                        }
                        if c != 0 {
                                for c != 8/bitdepth {
                                        b = b << uint(bitdepth)
                                        c++
                                }
                                fmt.Fprintf(w, "%02x", b)
                        }
                }
                io.WriteString(w, "\n")
        }
        io.WriteString(w, "}\n")
}

func TestReader(t *testing.T) {
        names := filenames
        if testing.Short() {
                names = filenamesShort
        }
        for _, fn := range names {
                // Read the .png file.
                img, err := readPNG("testdata/pngsuite/" + fn + ".png")
                if err != nil {
                        t.Error(fn, err)
                        continue
                }

                if fn == "basn4a16" {
                        // basn4a16.sng is gray + alpha but sng() will produce true color + alpha
                        // so we just check a single random pixel.
                        c := img.At(2, 1).(color.NRGBA64)
                        if c.R != 0x11a7 || c.G != 0x11a7 || c.B != 0x11a7 || c.A != 0x1085 {
                                t.Error(fn, fmt.Errorf("wrong pixel value at (2, 1): %x", c))
                        }
                        continue
                }

                piper, pipew := io.Pipe()
                pb := bufio.NewScanner(piper)
                go sng(pipew, fn, img)
                defer piper.Close()

                // Read the .sng file.
                sf, err := os.Open("testdata/pngsuite/" + fn + ".sng")
                if err != nil {
                        t.Error(fn, err)
                        continue
                }
                defer sf.Close()
                sb := bufio.NewScanner(sf)
                if err != nil {
                        t.Error(fn, err)
                        continue
                }

                // Compare the two, in SNG format, line by line.
                for {
                        pdone := !pb.Scan()
                        sdone := !sb.Scan()
                        if pdone && sdone {
                                break
                        }
                        if pdone || sdone {
                                t.Errorf("%s: Different sizes", fn)
                                break
                        }
                        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%s\nversus\n%s\n", fn, ps, ss)
                                break
                        }
                }
                if pb.Err() != nil {
                        t.Error(fn, pb.Err())
                }
                if sb.Err() != nil {
                        t.Error(fn, sb.Err())
                }
        }
}

var readerErrors = []struct {
        file string
        err  string
}{
        {"invalid-zlib.png", "zlib: invalid checksum"},
        {"invalid-crc32.png", "invalid checksum"},
        {"invalid-noend.png", "unexpected EOF"},
        {"invalid-trunc.png", "unexpected EOF"},
}

func TestReaderError(t *testing.T) {
        for _, tt := range readerErrors {
                img, err := readPNG("testdata/" + tt.file)
                if err == nil {
                        t.Errorf("decoding %s: missing error", tt.file)
                        continue
                }
                if !strings.Contains(err.Error(), tt.err) {
                        t.Errorf("decoding %s: %s, want %s", tt.file, err, tt.err)
                }
                if img != nil {
                        t.Errorf("decoding %s: have image + error", tt.file)
                }
        }
}

func TestPalettedDecodeConfig(t *testing.T) {
        for _, fn := range filenamesPaletted {
                f, err := os.Open("testdata/pngsuite/" + fn + ".png")
                if err != nil {
                        t.Errorf("%s: open failed: %v", fn, err)
                        continue
                }
                defer f.Close()
                cfg, err := DecodeConfig(f)
                if err != nil {
                        t.Errorf("%s: %v", fn, err)
                        continue
                }
                pal, ok := cfg.ColorModel.(color.Palette)
                if !ok {
                        t.Errorf("%s: expected paletted color model", fn)
                        continue
                }
                if pal == nil {
                        t.Errorf("%s: palette not initialized", fn)
                        continue
                }
        }
}

func TestInterlaced(t *testing.T) {
        a, err := readPNG("testdata/gray-gradient.png")
        if err != nil {
                t.Fatal(err)
        }
        b, err := readPNG("testdata/gray-gradient.interlaced.png")
        if err != nil {
                t.Fatal(err)
        }
        if !reflect.DeepEqual(a, b) {
                t.Fatalf("decodings differ:\nnon-interlaced:\n%#v\ninterlaced:\n%#v", a, b)
        }
}

func TestIncompleteIDATOnRowBoundary(t *testing.T) {
        // The following is an invalid 1x2 grayscale PNG image. The header is OK,
        // but the zlib-compressed IDAT payload contains two bytes "\x02\x00",
        // which is only one row of data (the leading "\x02" is a row filter).
        const (
                ihdr = "\x00\x00\x00\x0dIHDR\x00\x00\x00\x01\x00\x00\x00\x02\x08\x00\x00\x00\x00\xbc\xea\xe9\xfb"
                idat = "\x00\x00\x00\x0eIDAT\x78\x9c\x62\x62\x00\x04\x00\x00\xff\xff\x00\x06\x00\x03\xfa\xd0\x59\xae"
                iend = "\x00\x00\x00\x00IEND\xae\x42\x60\x82"
        )
        _, err := Decode(strings.NewReader(pngHeader + ihdr + idat + iend))
        if err == nil {
                t.Fatal("got nil error, want non-nil")
        }
}

func TestTrailingIDATChunks(t *testing.T) {
        // The following is a valid 1x1 PNG image containing color.Gray{255} and
        // a trailing zero-length IDAT chunk (see PNG specification section 12.9):
        const (
                ihdr      = "\x00\x00\x00\x0dIHDR\x00\x00\x00\x01\x00\x00\x00\x01\x08\x00\x00\x00\x00\x3a\x7e\x9b\x55"
                idatWhite = "\x00\x00\x00\x0eIDAT\x78\x9c\x62\xfa\x0f\x08\x00\x00\xff\xff\x01\x05\x01\x02\x5a\xdd\x39\xcd"
                idatZero  = "\x00\x00\x00\x00IDAT\x35\xaf\x06\x1e"
                iend      = "\x00\x00\x00\x00IEND\xae\x42\x60\x82"
        )
        _, err := Decode(strings.NewReader(pngHeader + ihdr + idatWhite + idatZero + iend))
        if err != nil {
                t.Fatalf("decoding valid image: %v", err)
        }

        // Non-zero-length trailing IDAT chunks should be ignored (recoverable error).
        // The following chunk contains a single pixel with color.Gray{0}.
        const idatBlack = "\x00\x00\x00\x0eIDAT\x78\x9c\x62\x62\x00\x04\x00\x00\xff\xff\x00\x06\x00\x03\xfa\xd0\x59\xae"

        img, err := Decode(strings.NewReader(pngHeader + ihdr + idatWhite + idatBlack + iend))
        if err != nil {
                t.Fatalf("trailing IDAT not ignored: %v", err)
        }
        if img.At(0, 0) == (color.Gray{0}) {
                t.Fatal("decoded image from trailing IDAT chunk")
        }
}

func TestMultipletRNSChunks(t *testing.T) {
        /*
                The following is a valid 1x1 paletted PNG image with a 1-element palette
                containing color.NRGBA{0xff, 0x00, 0x00, 0x7f}:
                        0000000: 8950 4e47 0d0a 1a0a 0000 000d 4948 4452  .PNG........IHDR
                        0000010: 0000 0001 0000 0001 0803 0000 0028 cb34  .............(.4
                        0000020: bb00 0000 0350 4c54 45ff 0000 19e2 0937  .....PLTE......7
                        0000030: 0000 0001 7452 4e53 7f80 5cb4 cb00 0000  ....tRNS..\.....
                        0000040: 0e49 4441 5478 9c62 6200 0400 00ff ff00  .IDATx.bb.......
                        0000050: 0600 03fa d059 ae00 0000 0049 454e 44ae  .....Y.....IEND.
                        0000060: 4260 82                                  B`.
                Dropping the tRNS chunk makes that color's alpha 0xff instead of 0x7f.
        */
        const (
                ihdr = "\x00\x00\x00\x0dIHDR\x00\x00\x00\x01\x00\x00\x00\x01\x08\x03\x00\x00\x00\x28\xcb\x34\xbb"
                plte = "\x00\x00\x00\x03PLTE\xff\x00\x00\x19\xe2\x09\x37"
                trns = "\x00\x00\x00\x01tRNS\x7f\x80\x5c\xb4\xcb"
                idat = "\x00\x00\x00\x0eIDAT\x78\x9c\x62\x62\x00\x04\x00\x00\xff\xff\x00\x06\x00\x03\xfa\xd0\x59\xae"
                iend = "\x00\x00\x00\x00IEND\xae\x42\x60\x82"
        )
        for i := 0; i < 4; i++ {
                var b []byte
                b = append(b, pngHeader...)
                b = append(b, ihdr...)
                b = append(b, plte...)
                for j := 0; j < i; j++ {
                        b = append(b, trns...)
                }
                b = append(b, idat...)
                b = append(b, iend...)

                var want color.Color
                m, err := Decode(bytes.NewReader(b))
                switch i {
                case 0:
                        if err != nil {
                                t.Errorf("%d tRNS chunks: %v", i, err)
                                continue
                        }
                        want = color.RGBA{0xff, 0x00, 0x00, 0xff}
                case 1:
                        if err != nil {
                                t.Errorf("%d tRNS chunks: %v", i, err)
                                continue
                        }
                        want = color.NRGBA{0xff, 0x00, 0x00, 0x7f}
                default:
                        if err == nil {
                                t.Errorf("%d tRNS chunks: got nil error, want non-nil", i)
                        }
                        continue
                }
                if got := m.At(0, 0); got != want {
                        t.Errorf("%d tRNS chunks: got %T %v, want %T %v", i, got, got, want, want)
                }
        }
}

func TestUnknownChunkLengthUnderflow(t *testing.T) {
        data := []byte{0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0xff, 0xff,
                0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x06, 0xf4, 0x7c, 0x55, 0x04, 0x1a,
                0xd3, 0x11, 0x9a, 0x73, 0x00, 0x00, 0xf8, 0x1e, 0xf3, 0x2e, 0x00, 0x00,
                0x01, 0x00, 0xff, 0xff, 0xff, 0xff, 0x07, 0xf4, 0x7c, 0x55, 0x04, 0x1a,
                0xd3}
        _, err := Decode(bytes.NewReader(data))
        if err == nil {
                t.Errorf("Didn't fail reading an unknown chunk with length 0xffffffff")
        }
}

func TestGray8Transparent(t *testing.T) {
        // These bytes come from https://github.com/golang/go/issues/19553
        m, err := Decode(bytes.NewReader([]byte{
                0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
                0x00, 0x00, 0x00, 0x0f, 0x00, 0x00, 0x00, 0x0b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x85, 0x2c, 0x88,
                0x80, 0x00, 0x00, 0x00, 0x02, 0x74, 0x52, 0x4e, 0x53, 0x00, 0xff, 0x5b, 0x91, 0x22, 0xb5, 0x00,
                0x00, 0x00, 0x02, 0x62, 0x4b, 0x47, 0x44, 0x00, 0xff, 0x87, 0x8f, 0xcc, 0xbf, 0x00, 0x00, 0x00,
                0x09, 0x70, 0x48, 0x59, 0x73, 0x00, 0x00, 0x0a, 0xf0, 0x00, 0x00, 0x0a, 0xf0, 0x01, 0x42, 0xac,
                0x34, 0x98, 0x00, 0x00, 0x00, 0x07, 0x74, 0x49, 0x4d, 0x45, 0x07, 0xd5, 0x04, 0x02, 0x12, 0x11,
                0x11, 0xf7, 0x65, 0x3d, 0x8b, 0x00, 0x00, 0x00, 0x4f, 0x49, 0x44, 0x41, 0x54, 0x08, 0xd7, 0x63,
                0xf8, 0xff, 0xff, 0xff, 0xb9, 0xbd, 0x70, 0xf0, 0x8c, 0x01, 0xc8, 0xaf, 0x6e, 0x99, 0x02, 0x05,
                0xd9, 0x7b, 0xc1, 0xfc, 0x6b, 0xff, 0xa1, 0xa0, 0x87, 0x30, 0xff, 0xd9, 0xde, 0xbd, 0xd5, 0x4b,
                0xf7, 0xee, 0xfd, 0x0e, 0xe3, 0xef, 0xcd, 0x06, 0x19, 0x14, 0xf5, 0x1e, 0xce, 0xef, 0x01, 0x31,
                0x92, 0xd7, 0x82, 0x41, 0x31, 0x9c, 0x3f, 0x07, 0x02, 0xee, 0xa1, 0xaa, 0xff, 0xff, 0x9f, 0xe1,
                0xd9, 0x56, 0x30, 0xf8, 0x0e, 0xe5, 0x03, 0x00, 0xa9, 0x42, 0x84, 0x3d, 0xdf, 0x8f, 0xa6, 0x8f,
                0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
        }))
        if err != nil {
                t.Fatalf("Decode: %v", err)
        }

        const hex = "0123456789abcdef"
        var got []byte
        bounds := m.Bounds()
        for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
                for x := bounds.Min.X; x < bounds.Max.X; x++ {
                        if r, _, _, a := m.At(x, y).RGBA(); a != 0 {
                                got = append(got,
                                        hex[0x0f&(r>>12)],
                                        hex[0x0f&(r>>8)],
                                        ' ',
                                )
                        } else {
                                got = append(got,
                                        '.',
                                        '.',
                                        ' ',
                                )
                        }
                }
                got = append(got, '\n')
        }

        const want = "" +
                ".. .. .. ce bd bd bd bd bd bd bd bd bd bd e6 \n" +
                ".. .. .. 7b 84 94 94 94 94 94 94 94 94 6b bd \n" +
                ".. .. .. 7b d6 .. .. .. .. .. .. .. .. 8c bd \n" +
                ".. .. .. 7b d6 .. .. .. .. .. .. .. .. 8c bd \n" +
                ".. .. .. 7b d6 .. .. .. .. .. .. .. .. 8c bd \n" +
                "e6 bd bd 7b a5 bd bd f7 .. .. .. .. .. 8c bd \n" +
                "bd 6b 94 94 94 94 5a ef .. .. .. .. .. 8c bd \n" +
                "bd 8c .. .. .. .. 63 ad ad ad ad ad ad 73 bd \n" +
                "bd 8c .. .. .. .. 63 9c 9c 9c 9c 9c 9c 9c de \n" +
                "bd 6b 94 94 94 94 5a ef .. .. .. .. .. .. .. \n" +
                "e6 b5 b5 b5 b5 b5 b5 f7 .. .. .. .. .. .. .. \n"

        if string(got) != want {
                t.Errorf("got:\n%swant:\n%s", got, want)
        }
}

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)
}

func BenchmarkDecodeInterlacing(b *testing.B) {
        benchmarkDecode(b, "testdata/benchRGB-interlace.png", 4)
}