src/liblzma/check/crc32_small.c

   1 // SPDX-License-Identifier: 0BSD
   2
   3 ///////////////////////////////////////////////////////////////////////////////
   4 //
   5 /// \file       crc32_small.c
   6 /// \brief      CRC32 calculation (size-optimized)
   7 //
   8 //  Author:     Lasse Collin
   9 //
  10 ///////////////////////////////////////////////////////////////////////////////
  11
  12 #include "check.h"
  13
  14
  15 uint32_t lzma_crc32_table[1][256];
  16
  17
  18 #ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
  19 __attribute__((__constructor__))
  20 #endif
  21 static void
  22 crc32_init(void)
  23 {
  24         static const uint32_t poly32 = UINT32_C(0xEDB88320);
  25
  26         for (size_t b = 0; b < 256; ++b) {
  27                 uint32_t r = b;
  28                 for (size_t i = 0; i < 8; ++i) {
  29                         if (r & 1)
  30                                 r = (r >> 1) ^ poly32;
  31                         else
  32                                 r >>= 1;
  33                 }
  34
  35                 lzma_crc32_table[0][b] = r;
  36         }
  37
  38         return;
  39 }
  40
  41
  42 #ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
  43 extern void
  44 lzma_crc32_init(void)
  45 {
  46         mythread_once(crc32_init);
  47         return;
  48 }
  49 #endif
  50
  51
  52 extern LZMA_API(uint32_t)
  53 lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
  54 {
  55 #ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
  56         lzma_crc32_init();
  57 #endif
  58
  59         crc = ~crc;
  60
  61         while (size != 0) {
  62                 crc = lzma_crc32_table[0][*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
  63                 --size;
  64         }
  65
  66         return ~crc;
  67 }