checksum.cpp

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//---------------------------------------------------------------------------
//
// Checksum.cpp: Checksum Routines Implementation
//
//---------------------------------------------------------------------------

#include "StdAfx.h"
#include "Checksum.h"

DWORD __cdecl adler32(DWORD adler, BYTE* buf, int len)
{
    // @WARNING: assume the buffer is always non-NULL
    // if (! buf) return 1;

    DWORD s1 = adler & 0xffff;
    DWORD s2 = (adler >> 16) & 0xffff;

    while (len > 0)
    {
        int k = len < NMAX ? len : NMAX;
        len -= k;

        while (k >= 16)
        {
            s1 += buf[0]; s2 += s1;
            s1 += buf[1]; s2 += s1;
            s1 += buf[2]; s2 += s1;
            s1 += buf[3]; s2 += s1;
            s1 += buf[4]; s2 += s1;
            s1 += buf[5]; s2 += s1;
            s1 += buf[6]; s2 += s1;
            s1 += buf[7]; s2 += s1;
            s1 += buf[8]; s2 += s1;
            s1 += buf[9]; s2 += s1;
            s1 += buf[10]; s2 += s1;
            s1 += buf[11]; s2 += s1;
            s1 += buf[12]; s2 += s1;
            s1 += buf[13]; s2 += s1;
            s1 += buf[14]; s2 += s1;
            s1 += buf[15]; s2 += s1;
            buf += 16;
            k -= 16;
        }
        while (k--)
        {
            s1 += *buf++;
            s2 += s1;
        }

        s1 %= BASE;
        s2 %= BASE;
    }

    return (s2 << 16) | s1;
}

DWORD crc32(DWORD crc, BYTE* buf, int len)
{
    // @WARNING: assume the buffer is always non-NULL
    // if (! buf) return 0;

    crc ^= 0xffffffffL;

    while (len >= 8)
    {
        crc = crc_table[(int(crc) ^ (*buf++)) & 0xff] ^ (crc >> 8);
        crc = crc_table[(int(crc) ^ (*buf++)) & 0xff] ^ (crc >> 8);
        crc = crc_table[(int(crc) ^ (*buf++)) & 0xff] ^ (crc >> 8);
        crc = crc_table[(int(crc) ^ (*buf++)) & 0xff] ^ (crc >> 8);
        crc = crc_table[(int(crc) ^ (*buf++)) & 0xff] ^ (crc >> 8);
        crc = crc_table[(int(crc) ^ (*buf++)) & 0xff] ^ (crc >> 8);
        crc = crc_table[(int(crc) ^ (*buf++)) & 0xff] ^ (crc >> 8);
        crc = crc_table[(int(crc) ^ (*buf++)) & 0xff] ^ (crc >> 8);
        len -= 8;
    }

    if (len) do
    {
        crc = crc_table[((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8);
    } while (--len);

    return crc ^ 0xffffffffL;
}