src/liblzma/check/crc64.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       crc64.c
   4 /// \brief      CRC64 calculation
   5 //
   6 //  This code has been put into the public domain.
   7 //
   8 //  This library is distributed in the hope that it will be useful,
   9 //  but WITHOUT ANY WARRANTY; without even the implied warranty of
  10 //  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  11 //
  12 ///////////////////////////////////////////////////////////////////////////////
  13
  14 #include "check.h"
  15 #include "crc_macros.h"
  16
  17
  18 #ifdef WORDS_BIGENDIAN
  19 #       define A1(x) ((x) >> 56)
  20 #else
  21 #       define A1 A
  22 #endif
  23
  24
  25 // See comments in crc32.c.
  26 extern uint64_t
  27 lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
  28 {
  29         crc = ~crc;
  30
  31 #ifdef WORDS_BIGENDIAN
  32         crc = bswap_64(crc);
  33 #endif
  34
  35         if (size > 4) {
  36                 while ((uintptr_t)(buf) & 3) {
  37                         crc = lzma_crc64_table[0][*buf++ ^ A1(crc)] ^ S8(crc);
  38                         --size;
  39                 }
  40
  41                 const uint8_t *const limit = buf + (size & ~(size_t)(3));
  42                 size &= (size_t)(3);
  43
  44                 // Calculate the CRC64 using the slice-by-four algorithm.
  45                 //
  46                 // In contrast to CRC32 code, this one seems to be fastest
  47                 // with -O3 -fomit-frame-pointer.
  48                 while (buf < limit) {
  49 #ifdef WORDS_BIGENDIAN
  50                         const uint32_t tmp = (crc >> 32) ^ *(uint32_t *)(buf);
  51 #else
  52                         const uint32_t tmp = crc ^ *(uint32_t *)(buf);
  53 #endif
  54                         buf += 4;
  55
  56                         // It is critical for performance, that
  57                         // the crc variable is XORed between the
  58                         // two table-lookup pairs.
  59                         crc = lzma_crc64_table[3][A(tmp)]
  60                             ^ lzma_crc64_table[2][B(tmp)]
  61                             ^ S32(crc)
  62                             ^ lzma_crc64_table[1][C(tmp)]
  63                             ^ lzma_crc64_table[0][D(tmp)];
  64                 }
  65         }
  66
  67         while (size-- != 0)
  68                 crc = lzma_crc64_table[0][*buf++ ^ A1(crc)] ^ S8(crc);
  69
  70 #ifdef WORDS_BIGENDIAN
  71         crc = bswap_64(crc);
  72 #endif
  73
  74         return ~crc;
  75 }