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-rw-r--r--src/image/png/paeth_test.go91
1 files changed, 91 insertions, 0 deletions
diff --git a/src/image/png/paeth_test.go b/src/image/png/paeth_test.go
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+++ b/src/image/png/paeth_test.go
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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 slowAbs(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 := slowAbs(p - int(a))
+ pb := slowAbs(p - int(b))
+ pc := slowAbs(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
+ }
+ }
+ }
+}