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// 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
}
}
}
}
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