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  #ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
      20  __attribute__((__constructor__))
      21  #endif
      22  static void
      23  crc32_init(void)
      24  {
      25  	static const uint32_t poly32 = UINT32_C(0xEDB88320);
      26  
      27  	for (size_t b = 0; b < 256; ++b) {
      28  		uint32_t r = b;
      29  		for (size_t i = 0; i < 8; ++i) {
      30  			if (r & 1)
      31  				r = (r >> 1) ^ poly32;
      32  			else
      33  				r >>= 1;
      34  		}
      35  
      36  		lzma_crc32_table[0][b] = r;
      37  	}
      38  
      39  	return;
      40  }
      41  
      42  
      43  #ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
      44  extern void
      45  lzma_crc32_init(void)
      46  {
      47  	mythread_once(crc32_init);
      48  	return;
      49  }
      50  #endif
      51  
      52  
      53  extern LZMA_API(uint32_t)
      54  lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
      55  {
      56  #ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
      57  	lzma_crc32_init();
      58  #endif
      59  
      60  	crc = ~crc;
      61  
      62  	while (size != 0) {
      63  		crc = lzma_crc32_table[0][*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
      64  		--size;
      65  	}
      66  
      67  	return ~crc;
      68  }