text: ///////////////////////////////////////////////////////////////////////////////
  //
  /// \file       crc32.c
  /// \brief      CRC32 calculation
  ///
  /// Calculate the CRC32 using the slice-by-eight algorithm.
  /// It is explained in this document:
  /// http://www.intel.com/technology/comms/perfnet/download/CRC_generators.pdf
  /// The code in this file is not the same as in Intel's paper, but
  /// the basic principle is identical.
  //
  //  Author:     Lasse Collin
  //
  //  This file has been put into the public domain.
  //  You can do whatever you want with this file.
  //
  ///////////////////////////////////////////////////////////////////////////////
  
  #include "check.h"
  #include "crc_macros.h"
  
  // If you make any changes, do some benchmarking! Seemingly unrelated
  // changes can very easily ruin the performance (and very probably is
  // very compiler dependent).
  extern LZMA_API(uint32_t)
      lzma_crc32(const uint8_t* buf, size_t size, uint32_t crc)
  {
      crc = ~crc;
  
  #ifdef WORDS_BIGENDIAN
      crc = bswap32(crc);
  #endif
  
      if (size > 8)
      {
          // Fix the alignment, if needed. The if statement above
          // ensures that this won't read past the end of buf[].
          while ((uintptr_t)(buf)&7)
          {
              crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
              --size;
          }
  
          // Calculate the position where to stop.
          const uint8_t* const limit = buf + (size & ~(size_t)(7));
  
          // Calculate how many bytes must be calculated separately
          // before returning the result.
          size &= (size_t)(7);
  
          // Calculate the CRC32 using the slice-by-eight algorithm.
          while (buf < limit)
          {
              crc ^= *(const uint32_t*)(buf);
              buf += 4;
  
              crc = lzma_crc32_table[7][A(crc)] ^ lzma_crc32_table[6][B(crc)] ^
                    lzma_crc32_table[5][C(crc)] ^ lzma_crc32_table[4][D(crc)];
  
              const uint32_t tmp = *(const uint32_t*)(buf);
              buf += 4;
  
              // At least with some compilers, it is critical for
              // performance, that the crc variable is XORed
              // between the two table-lookup pairs.
              crc = lzma_crc32_table[3][A(tmp)] ^ lzma_crc32_table[2][B(tmp)] ^
                    crc ^ lzma_crc32_table[1][C(tmp)] ^
                    lzma_crc32_table[0][D(tmp)];
          }
      }
  
      while (size-- != 0)
          crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
  
  #ifdef WORDS_BIGENDIAN
      crc = bswap32(crc);
  #endif
  
      return ~crc;
  }
  