source: vbox/trunk/src/libs/liblzma-5.4.1/check/crc32_small.c

///////////////////////////////////////////////////////////////////////////////
//
/// \file       crc32_small.c
/// \brief      CRC32 calculation (size-optimized)
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "check.h"


uint32_t lzma_crc32_table[1][256];


#ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
__attribute__((__constructor__))
#endif
static void
crc32_init(void)
{
        static const uint32_t poly32 = UINT32_C(0xEDB88320);

        for (size_t b = 0; b < 256; ++b) {
                uint32_t r = b;
                for (size_t i = 0; i < 8; ++i) {
                        if (r & 1)
                                r = (r >> 1) ^ poly32;
                        else
                                r >>= 1;
                }

                lzma_crc32_table[0][b] = r;
        }

        return;
}


#ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
extern void
lzma_crc32_init(void)
{
        mythread_once(crc32_init);
        return;
}
#endif


extern LZMA_API(uint32_t)
lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
{
#ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
        lzma_crc32_init();
#endif

        crc = ~crc;

        while (size != 0) {
                crc = lzma_crc32_table[0][*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
                --size;
        }

        return ~crc;
}