1 // Copyright 2012 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package png 6 7 import ( 8 "bytes" 9 "math/rand" 10 "testing" 11 ) 12 13 func slowAbs(x int) int { 14 if x < 0 { 15 return -x 16 } 17 return x 18 } 19 20 // slowPaeth is a slow but simple implementation of the Paeth function. 21 // It is a straight port of the sample code in the PNG spec, section 9.4. 22 func slowPaeth(a, b, c uint8) uint8 { 23 p := int(a) + int(b) - int(c) 24 pa := slowAbs(p - int(a)) 25 pb := slowAbs(p - int(b)) 26 pc := slowAbs(p - int(c)) 27 if pa <= pb && pa <= pc { 28 return a 29 } else if pb <= pc { 30 return b 31 } 32 return c 33 } 34 35 // slowFilterPaeth is a slow but simple implementation of func filterPaeth. 36 func slowFilterPaeth(cdat, pdat []byte, bytesPerPixel int) { 37 for i := 0; i < bytesPerPixel; i++ { 38 cdat[i] += paeth(0, pdat[i], 0) 39 } 40 for i := bytesPerPixel; i < len(cdat); i++ { 41 cdat[i] += paeth(cdat[i-bytesPerPixel], pdat[i], pdat[i-bytesPerPixel]) 42 } 43 } 44 45 func TestPaeth(t *testing.T) { 46 for a := 0; a < 256; a += 15 { 47 for b := 0; b < 256; b += 15 { 48 for c := 0; c < 256; c += 15 { 49 got := paeth(uint8(a), uint8(b), uint8(c)) 50 want := slowPaeth(uint8(a), uint8(b), uint8(c)) 51 if got != want { 52 t.Errorf("a, b, c = %d, %d, %d: got %d, want %d", a, b, c, got, want) 53 } 54 } 55 } 56 } 57 } 58 59 func BenchmarkPaeth(b *testing.B) { 60 for i := 0; i < b.N; i++ { 61 paeth(uint8(i>>16), uint8(i>>8), uint8(i)) 62 } 63 } 64 65 func TestPaethDecode(t *testing.T) { 66 pdat0 := make([]byte, 32) 67 pdat1 := make([]byte, 32) 68 pdat2 := make([]byte, 32) 69 cdat0 := make([]byte, 32) 70 cdat1 := make([]byte, 32) 71 cdat2 := make([]byte, 32) 72 r := rand.New(rand.NewSource(1)) 73 for bytesPerPixel := 1; bytesPerPixel <= 8; bytesPerPixel++ { 74 for i := 0; i < 100; i++ { 75 for j := range pdat0 { 76 pdat0[j] = uint8(r.Uint32()) 77 cdat0[j] = uint8(r.Uint32()) 78 } 79 copy(pdat1, pdat0) 80 copy(pdat2, pdat0) 81 copy(cdat1, cdat0) 82 copy(cdat2, cdat0) 83 filterPaeth(cdat1, pdat1, bytesPerPixel) 84 slowFilterPaeth(cdat2, pdat2, bytesPerPixel) 85 if !bytes.Equal(cdat1, cdat2) { 86 t.Errorf("bytesPerPixel: %d\npdat0: % x\ncdat0: % x\ngot: % x\nwant: % x", bytesPerPixel, pdat0, cdat0, cdat1, cdat2) 87 break 88 } 89 } 90 } 91 } 92
