The R Project SVN R

///////////////////////////////////////////////////////////////////////////////
//
/// \file       crc64_small.c
/// \brief      CRC64 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"


static uint64_t crc64_table[256];


static void
crc64_init(void)
{
    static const uint64_t poly64 = UINT64_C(0xC96C5795D7870F42);

    for (size_t b = 0; b < 256; ++b) {
        uint64_t r = b;
        for (size_t i = 0; i < 8; ++i) {
            if (r & 1)
                r = (r >> 1) ^ poly64;
            else
                r >>= 1;
        }

        crc64_table[b] = r;
    }

    return;
}


extern LZMA_API(uint64_t)
lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
{
    mythread_once(crc64_init);

    crc = ~crc;

    while (size != 0) {
        crc = crc64_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
        --size;
    }

    return ~crc;
}