xz/xz_crc64.c

   1 /*
   2  * CRC64 using the polynomial from ECMA-182
   3  *
   4  * This file is similar to xz_crc32.c. See the comments there.
   5  *
   6  * Authors: Lasse Collin <lasse.collin@tukaani.org>
   7  *          Igor Pavlov <http://7-zip.org/>
   8  *
   9  * This file has been put into the public domain.
  10  * You can do whatever you want with this file.
  11  */
  12
  13 #include "xz_private.h"
  14
  15 #ifndef STATIC_RW_DATA
  16 #       define STATIC_RW_DATA static
  17 #endif
  18
  19 STATIC_RW_DATA uint64_t xz_crc64_table[256];
  20
  21 XZ_EXTERN void xz_crc64_init(void)
  22 {
  23         const uint64_t poly = 0xC96C5795D7870F42;
  24
  25         uint32_t i;
  26         uint32_t j;
  27         uint64_t r;
  28
  29         for (i = 0; i < 256; ++i) {
  30                 r = i;
  31                 for (j = 0; j < 8; ++j)
  32                         r = (r >> 1) ^ (poly & ~((r & 1) - 1));
  33
  34                 xz_crc64_table[i] = r;
  35         }
  36
  37         return;
  38 }
  39
  40 XZ_EXTERN uint64_t xz_crc64(const uint8_t *buf, size_t size, uint64_t crc)
  41 {
  42         crc = ~crc;
  43
  44         while (size != 0) {
  45                 crc = xz_crc64_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
  46                 --size;
  47         }
  48
  49         return ~crc;
  50 }