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crc32.c 1.9 KB

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  1. /* vi: set sw=4 ts=4: */
  2. /*
  3. * CRC32 table fill function
  4. * Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com>
  5. * (I can't really claim much credit however, as the algorithm is
  6. * very well-known)
  7. *
  8. * The following function creates a CRC32 table depending on whether
  9. * a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is
  10. * required. Admittedly, there are other CRC32 polynomials floating
  11. * around, but Busybox doesn't use them.
  12. *
  13. * endian = 1: big-endian
  14. * endian = 0: little-endian
  15. *
  16. * Licensed under GPLv2, see file LICENSE in this source tree.
  17. */
  18. #include "libbb.h"
  19. uint32_t *global_crc32_table;
  20. uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian)
  21. {
  22. uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
  23. uint32_t c;
  24. unsigned i, j;
  25. if (!crc_table)
  26. crc_table = xmalloc(256 * sizeof(uint32_t));
  27. for (i = 0; i < 256; i++) {
  28. c = endian ? (i << 24) : i;
  29. for (j = 8; j; j--) {
  30. if (endian)
  31. c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1);
  32. else
  33. c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1);
  34. }
  35. *crc_table++ = c;
  36. }
  37. return crc_table - 256;
  38. }
  39. /* Common uses: */
  40. uint32_t* FAST_FUNC crc32_new_table_le(void)
  41. {
  42. return crc32_filltable(NULL, 0);
  43. }
  44. uint32_t* FAST_FUNC global_crc32_new_table_le(void)
  45. {
  46. global_crc32_table = crc32_new_table_le();
  47. return global_crc32_table;
  48. }
  49. uint32_t FAST_FUNC crc32_block_endian1(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
  50. {
  51. const void *end = (uint8_t*)buf + len;
  52. while (buf != end) {
  53. val = (val << 8) ^ crc_table[(val >> 24) ^ *(uint8_t*)buf];
  54. buf = (uint8_t*)buf + 1;
  55. }
  56. return val;
  57. }
  58. uint32_t FAST_FUNC crc32_block_endian0(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
  59. {
  60. const void *end = (uint8_t*)buf + len;
  61. while (buf != end) {
  62. val = crc_table[(uint8_t)val ^ *(uint8_t*)buf] ^ (val >> 8);
  63. buf = (uint8_t*)buf + 1;
  64. }
  65. return val;
  66. }