SkPackBits.cpp 3.1 KB

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