1 /*
2 * Copyright 2011 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7 #include "SkPackBits.h"
8
ComputeMaxSize8(size_t srcSize)9 size_t SkPackBits::ComputeMaxSize8(size_t srcSize) {
10 // worst case is the number of 8bit values + 1 byte per (up to) 128 entries.
11 return ((srcSize + 127) >> 7) + srcSize;
12 }
13
flush_same8(uint8_t dst[],uint8_t value,size_t count)14 static uint8_t* flush_same8(uint8_t dst[], uint8_t value, size_t count) {
15 while (count > 0) {
16 size_t n = count > 128 ? 128 : count;
17 *dst++ = (uint8_t)(n - 1);
18 *dst++ = (uint8_t)value;
19 count -= n;
20 }
21 return dst;
22 }
23
flush_diff8(uint8_t * SK_RESTRICT dst,const uint8_t * SK_RESTRICT src,size_t count)24 static uint8_t* flush_diff8(uint8_t* SK_RESTRICT dst,
25 const uint8_t* SK_RESTRICT src, size_t count) {
26 while (count > 0) {
27 size_t n = count > 128 ? 128 : count;
28 *dst++ = (uint8_t)(n + 127);
29 memcpy(dst, src, n);
30 src += n;
31 dst += n;
32 count -= n;
33 }
34 return dst;
35 }
36
Pack8(const uint8_t * SK_RESTRICT src,size_t srcSize,uint8_t * SK_RESTRICT dst,size_t dstSize)37 size_t SkPackBits::Pack8(const uint8_t* SK_RESTRICT src, size_t srcSize,
38 uint8_t* SK_RESTRICT dst, size_t dstSize) {
39 if (dstSize < ComputeMaxSize8(srcSize)) {
40 return 0;
41 }
42
43 uint8_t* const origDst = dst;
44 const uint8_t* stop = src + srcSize;
45
46 for (intptr_t count = stop - src; count > 0; count = stop - src) {
47 if (1 == count) {
48 *dst++ = 0;
49 *dst++ = *src;
50 break;
51 }
52
53 unsigned value = *src;
54 const uint8_t* s = src + 1;
55
56 if (*s == value) { // accumulate same values...
57 do {
58 s++;
59 if (s == stop) {
60 break;
61 }
62 } while (*s == value);
63 dst = flush_same8(dst, value, SkToInt(s - src));
64 } else { // accumulate diff values...
65 do {
66 if (++s == stop) {
67 goto FLUSH_DIFF;
68 }
69 // only stop if we hit 3 in a row,
70 // otherwise we get bigger than compuatemax
71 } while (*s != s[-1] || s[-1] != s[-2]);
72 s -= 2; // back up so we don't grab the "same" values that follow
73 FLUSH_DIFF:
74 dst = flush_diff8(dst, src, SkToInt(s - src));
75 }
76 src = s;
77 }
78 return dst - origDst;
79 }
80
Unpack8(const uint8_t * SK_RESTRICT src,size_t srcSize,uint8_t * SK_RESTRICT dst,size_t dstSize)81 int SkPackBits::Unpack8(const uint8_t* SK_RESTRICT src, size_t srcSize,
82 uint8_t* SK_RESTRICT dst, size_t dstSize) {
83 uint8_t* const origDst = dst;
84 uint8_t* const endDst = dst + dstSize;
85 const uint8_t* stop = src + srcSize;
86
87 while (src < stop) {
88 unsigned n = *src++;
89 if (n <= 127) { // repeat count (n + 1)
90 n += 1;
91 if (dst >(endDst - n)) {
92 return 0;
93 }
94 memset(dst, *src++, n);
95 } else { // same count (n - 127)
96 n -= 127;
97 if (dst > (endDst - n)) {
98 return 0;
99 }
100 memcpy(dst, src, n);
101 src += n;
102 }
103 dst += n;
104 }
105 SkASSERT(src <= stop);
106 return SkToInt(dst - origDst);
107 }
108