src/liblzma/check/crc32_small.c

   1 ///////////////////////////////////////////////////////////////////////////////
   2 //
   3 /// \file       crc32_small.c
   4 /// \brief      CRC32 calculation (size-optimized)
   5 //
   6 //  Author:     Lasse Collin
   7 //
   8 //  This file has been put into the public domain.
   9 //  You can do whatever you want with this file.
  10 //
  11 ///////////////////////////////////////////////////////////////////////////////
  12
  13 #include "check.h"
  14
  15
  16 uint32_t lzma_crc32_table[1][256];
  17
  18
  19 static void
  20 crc32_init(void)
  21 {
  22         static const uint32_t poly32 = UINT32_C(0xEDB88320);
  23
  24         for (size_t b = 0; b < 256; ++b) {
  25                 uint32_t r = b;
  26                 for (size_t i = 0; i < 8; ++i) {
  27                         if (r & 1)
  28                                 r = (r >> 1) ^ poly32;
  29                         else
  30                                 r >>= 1;
  31                 }
  32
  33                 lzma_crc32_table[0][b] = r;
  34         }
  35
  36         return;
  37 }
  38
  39
  40 extern void
  41 lzma_crc32_init(void)
  42 {
  43         mythread_once(crc32_init);
  44         return;
  45 }
  46
  47
  48 extern LZMA_API(uint32_t)
  49 lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
  50 {
  51         lzma_crc32_init();
  52
  53         crc = ~crc;
  54
  55         while (size != 0) {
  56                 crc = lzma_crc32_table[0][*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
  57                 --size;
  58         }
  59
  60         return ~crc;
  61 }