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
8 #include "SkPackBits.h"
9 #include "SkTo.h"
10
11 #include <cstring>
12
ComputeMaxSize8(size_t srcSize)13 size_t SkPackBits::ComputeMaxSize8(size_t srcSize) {
14 // worst case is the number of 8bit values + 1 byte per (up to) 128 entries.
15 return ((srcSize + 127) >> 7) + srcSize;
16 }
17
flush_same8(uint8_t dst[],uint8_t value,size_t count)18 static uint8_t* flush_same8(uint8_t dst[], uint8_t value, size_t count) {
19 while (count > 0) {
20 size_t n = count > 128 ? 128 : count;
21 *dst++ = (uint8_t)(n - 1);
22 *dst++ = (uint8_t)value;
23 count -= n;
24 }
25 return dst;
26 }
27
flush_diff8(uint8_t * SK_RESTRICT dst,const uint8_t * SK_RESTRICT src,size_t count)28 static uint8_t* flush_diff8(uint8_t* SK_RESTRICT dst,
29 const uint8_t* SK_RESTRICT src, size_t count) {
30 while (count > 0) {
31 size_t n = count > 128 ? 128 : count;
32 *dst++ = (uint8_t)(n + 127);
33 memcpy(dst, src, n);
34 src += n;
35 dst += n;
36 count -= n;
37 }
38 return dst;
39 }
40
Pack8(const uint8_t * SK_RESTRICT src,size_t srcSize,uint8_t * SK_RESTRICT dst,size_t dstSize)41 size_t SkPackBits::Pack8(const uint8_t* SK_RESTRICT src, size_t srcSize,
42 uint8_t* SK_RESTRICT dst, size_t dstSize) {
43 if (dstSize < ComputeMaxSize8(srcSize)) {
44 return 0;
45 }
46
47 uint8_t* const origDst = dst;
48 const uint8_t* stop = src + srcSize;
49
50 for (intptr_t count = stop - src; count > 0; count = stop - src) {
51 if (1 == count) {
52 *dst++ = 0;
53 *dst++ = *src;
54 break;
55 }
56
57 unsigned value = *src;
58 const uint8_t* s = src + 1;
59
60 if (*s == value) { // accumulate same values...
61 do {
62 s++;
63 if (s == stop) {
64 break;
65 }
66 } while (*s == value);
67 dst = flush_same8(dst, value, SkToInt(s - src));
68 } else { // accumulate diff values...
69 do {
70 if (++s == stop) {
71 goto FLUSH_DIFF;
72 }
73 // only stop if we hit 3 in a row,
74 // otherwise we get bigger than compuatemax
75 } while (*s != s[-1] || s[-1] != s[-2]);
76 s -= 2; // back up so we don't grab the "same" values that follow
77 FLUSH_DIFF:
78 dst = flush_diff8(dst, src, SkToInt(s - src));
79 }
80 src = s;
81 }
82 return dst - origDst;
83 }
84
Unpack8(const uint8_t * SK_RESTRICT src,size_t srcSize,uint8_t * SK_RESTRICT dst,size_t dstSize)85 int SkPackBits::Unpack8(const uint8_t* SK_RESTRICT src, size_t srcSize,
86 uint8_t* SK_RESTRICT dst, size_t dstSize) {
87 uint8_t* const origDst = dst;
88 uint8_t* const endDst = dst + dstSize;
89 const uint8_t* stop = src + srcSize;
90
91 while (src < stop) {
92 unsigned n = *src++;
93 if (n <= 127) { // repeat count (n + 1)
94 n += 1;
95 if (dst > (endDst - n) || src >= stop) {
96 return 0;
97 }
98 memset(dst, *src++, n);
99 } else { // same count (n - 127)
100 n -= 127;
101 if (dst > (endDst - n) || src > (stop - n)) {
102 return 0;
103 }
104 memcpy(dst, src, n);
105 src += n;
106 }
107 dst += n;
108 }
109 SkASSERT(src <= stop);
110 SkASSERT(dst <= endDst);
111 return SkToInt(dst - origDst);
112 }
113