92 lines
2.2 KiB
Go
92 lines
2.2 KiB
Go
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package png
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import (
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"bytes"
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"math/rand"
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"testing"
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)
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func abs(x int) int {
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if x < 0 {
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return -x
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}
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return x
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}
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// slowPaeth is a slow but simple implementation of the Paeth function.
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// It is a straight port of the sample code in the PNG spec, section 9.4.
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func slowPaeth(a, b, c uint8) uint8 {
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p := int(a) + int(b) - int(c)
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pa := abs(p - int(a))
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pb := abs(p - int(b))
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pc := abs(p - int(c))
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if pa <= pb && pa <= pc {
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return a
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} else if pb <= pc {
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return b
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}
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return c
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}
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// slowFilterPaeth is a slow but simple implementation of func filterPaeth.
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func slowFilterPaeth(cdat, pdat []byte, bytesPerPixel int) {
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for i := 0; i < bytesPerPixel; i++ {
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cdat[i] += paeth(0, pdat[i], 0)
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}
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for i := bytesPerPixel; i < len(cdat); i++ {
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cdat[i] += paeth(cdat[i-bytesPerPixel], pdat[i], pdat[i-bytesPerPixel])
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}
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}
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func TestPaeth(t *testing.T) {
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for a := 0; a < 256; a += 15 {
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for b := 0; b < 256; b += 15 {
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for c := 0; c < 256; c += 15 {
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got := paeth(uint8(a), uint8(b), uint8(c))
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want := slowPaeth(uint8(a), uint8(b), uint8(c))
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if got != want {
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t.Errorf("a, b, c = %d, %d, %d: got %d, want %d", a, b, c, got, want)
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}
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}
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}
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}
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}
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func BenchmarkPaeth(b *testing.B) {
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for i := 0; i < b.N; i++ {
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paeth(uint8(i>>16), uint8(i>>8), uint8(i))
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}
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}
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func TestPaethDecode(t *testing.T) {
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pdat0 := make([]byte, 32)
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pdat1 := make([]byte, 32)
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pdat2 := make([]byte, 32)
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cdat0 := make([]byte, 32)
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cdat1 := make([]byte, 32)
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cdat2 := make([]byte, 32)
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r := rand.New(rand.NewSource(1))
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for bytesPerPixel := 1; bytesPerPixel <= 8; bytesPerPixel++ {
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for i := 0; i < 100; i++ {
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for j := range pdat0 {
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pdat0[j] = uint8(r.Uint32())
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cdat0[j] = uint8(r.Uint32())
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}
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copy(pdat1, pdat0)
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copy(pdat2, pdat0)
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copy(cdat1, cdat0)
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copy(cdat2, cdat0)
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filterPaeth(cdat1, pdat1, bytesPerPixel)
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slowFilterPaeth(cdat2, pdat2, bytesPerPixel)
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if !bytes.Equal(cdat1, cdat2) {
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t.Errorf("bytesPerPixel: %d\npdat0: % x\ncdat0: % x\ngot: % x\nwant: % x", bytesPerPixel, pdat0, cdat0, cdat1, cdat2)
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break
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}
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}
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}
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}
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