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
5package png
6
7import (
8	"bytes"
9	"math/rand"
10	"testing"
11)
12
13func 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.
22func 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.
36func 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
45func 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
59func 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
65func 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