paeth_test.go

Documentation: image/png

		 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
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