crc.c 5.2 KB

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  1. /*
  2. * copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
  3. *
  4. * This file is part of FFmpeg.
  5. *
  6. * FFmpeg is free software; you can redistribute it and/or
  7. * modify it under the terms of the GNU Lesser General Public
  8. * License as published by the Free Software Foundation; either
  9. * version 2.1 of the License, or (at your option) any later version.
  10. *
  11. * FFmpeg is distributed in the hope that it will be useful,
  12. * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13. * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14. * Lesser General Public License for more details.
  15. *
  16. * You should have received a copy of the GNU Lesser General Public
  17. * License along with FFmpeg; if not, write to the Free Software
  18. * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19. */
  20. #include "config.h"
  21. #include "common.h"
  22. #include "bswap.h"
  23. #include "crc.h"
  24. #if CONFIG_HARDCODED_TABLES
  25. #include "crc_data.h"
  26. #else
  27. static struct {
  28. uint8_t le;
  29. uint8_t bits;
  30. uint32_t poly;
  31. } av_crc_table_params[AV_CRC_MAX] = {
  32. [AV_CRC_8_ATM] = { 0, 8, 0x07 },
  33. [AV_CRC_16_ANSI] = { 0, 16, 0x8005 },
  34. [AV_CRC_16_CCITT] = { 0, 16, 0x1021 },
  35. [AV_CRC_32_IEEE] = { 0, 32, 0x04C11DB7 },
  36. [AV_CRC_32_IEEE_LE] = { 1, 32, 0xEDB88320 },
  37. };
  38. static AVCRC av_crc_table[AV_CRC_MAX][257];
  39. #endif
  40. /**
  41. * Initialize a CRC table.
  42. * @param ctx must be an array of size sizeof(AVCRC)*257 or sizeof(AVCRC)*1024
  43. * @param le If 1, the lowest bit represents the coefficient for the highest
  44. * exponent of the corresponding polynomial (both for poly and
  45. * actual CRC).
  46. * If 0, you must swap the CRC parameter and the result of av_crc
  47. * if you need the standard representation (can be simplified in
  48. * most cases to e.g. bswap16):
  49. * av_bswap32(crc << (32-bits))
  50. * @param bits number of bits for the CRC
  51. * @param poly generator polynomial without the x**bits coefficient, in the
  52. * representation as specified by le
  53. * @param ctx_size size of ctx in bytes
  54. * @return <0 on failure
  55. */
  56. int av_crc_init(AVCRC *ctx, int le, int bits, uint32_t poly, int ctx_size)
  57. {
  58. unsigned i, j;
  59. uint32_t c;
  60. if (bits < 8 || bits > 32 || poly >= (1LL << bits))
  61. return -1;
  62. if (ctx_size != sizeof(AVCRC) * 257 && ctx_size != sizeof(AVCRC) * 1024)
  63. return -1;
  64. for (i = 0; i < 256; i++) {
  65. if (le) {
  66. for (c = i, j = 0; j < 8; j++)
  67. c = (c >> 1) ^ (poly & (-(c & 1)));
  68. ctx[i] = c;
  69. } else {
  70. for (c = i << 24, j = 0; j < 8; j++)
  71. c = (c << 1) ^ ((poly << (32 - bits)) & (((int32_t) c) >> 31));
  72. ctx[i] = av_bswap32(c);
  73. }
  74. }
  75. ctx[256] = 1;
  76. #if !CONFIG_SMALL
  77. if (ctx_size >= sizeof(AVCRC) * 1024)
  78. for (i = 0; i < 256; i++)
  79. for (j = 0; j < 3; j++)
  80. ctx[256 *(j + 1) + i] =
  81. (ctx[256 * j + i] >> 8) ^ ctx[ctx[256 * j + i] & 0xFF];
  82. #endif
  83. return 0;
  84. }
  85. /**
  86. * Get an initialized standard CRC table.
  87. * @param crc_id ID of a standard CRC
  88. * @return a pointer to the CRC table or NULL on failure
  89. */
  90. const AVCRC *av_crc_get_table(AVCRCId crc_id)
  91. {
  92. #if !CONFIG_HARDCODED_TABLES
  93. if (!av_crc_table[crc_id][FF_ARRAY_ELEMS(av_crc_table[crc_id]) - 1])
  94. if (av_crc_init(av_crc_table[crc_id],
  95. av_crc_table_params[crc_id].le,
  96. av_crc_table_params[crc_id].bits,
  97. av_crc_table_params[crc_id].poly,
  98. sizeof(av_crc_table[crc_id])) < 0)
  99. return NULL;
  100. #endif
  101. return av_crc_table[crc_id];
  102. }
  103. /**
  104. * Calculate the CRC of a block.
  105. * @param crc CRC of previous blocks if any or initial value for CRC
  106. * @return CRC updated with the data from the given block
  107. *
  108. * @see av_crc_init() "le" parameter
  109. */
  110. uint32_t av_crc(const AVCRC *ctx, uint32_t crc,
  111. const uint8_t *buffer, size_t length)
  112. {
  113. const uint8_t *end = buffer + length;
  114. #if !CONFIG_SMALL
  115. if (!ctx[256]) {
  116. while (((intptr_t) buffer & 3) && buffer < end)
  117. crc = ctx[((uint8_t) crc) ^ *buffer++] ^ (crc >> 8);
  118. while (buffer < end - 3) {
  119. crc ^= av_le2ne32(*(const uint32_t *) buffer); buffer += 4;
  120. crc = ctx[3 * 256 + ( crc & 0xFF)] ^
  121. ctx[2 * 256 + ((crc >> 8 ) & 0xFF)] ^
  122. ctx[1 * 256 + ((crc >> 16) & 0xFF)] ^
  123. ctx[0 * 256 + ((crc >> 24) )];
  124. }
  125. }
  126. #endif
  127. while (buffer < end)
  128. crc = ctx[((uint8_t) crc) ^ *buffer++] ^ (crc >> 8);
  129. return crc;
  130. }
  131. #ifdef TEST
  132. #undef printf
  133. int main(void)
  134. {
  135. uint8_t buf[1999];
  136. int i;
  137. int p[4][3] = { { AV_CRC_32_IEEE_LE, 0xEDB88320, 0x3D5CDD04 },
  138. { AV_CRC_32_IEEE , 0x04C11DB7, 0xC0F5BAE0 },
  139. { AV_CRC_16_ANSI , 0x8005 , 0x1FBB },
  140. { AV_CRC_8_ATM , 0x07 , 0xE3 }
  141. };
  142. const AVCRC *ctx;
  143. for (i = 0; i < sizeof(buf); i++)
  144. buf[i] = i + i * i;
  145. for (i = 0; i < 4; i++) {
  146. ctx = av_crc_get_table(p[i][0]);
  147. printf("crc %08X = %X\n", p[i][1], av_crc(ctx, 0, buf, sizeof(buf)));
  148. }
  149. return 0;
  150. }
  151. #endif