Fast implementation of popular checksum algorithms in simple C language.

checksums.c

#include <stddef.h>

unsigned int adler32(unsigned int adler, const unsigned char* buf, size_t len)
{
    unsigned int a, b;
    if (adler)
    {
        a = adler & 0x0000ffff;
        b = (adler >> 16) & 0x0000ffff;
    }
    else
    {
        a = 1;
        b = 0;
    }
    while (len--)
    {
        a = (a + *buf++) % 65521;
        b = (b + a) % 65521;
    }
    return (b << 16) + a;
}

unsigned int crc32(unsigned int crc, const unsigned char* buf, size_t len)
{
    int k;
    crc = ~crc;
    while (len--)
    {
        crc ^= *buf++;
        for (k = 0; k < 8; k++)
            crc = (crc >> 1) ^ (0xedb88320 & (0 - (crc & 1)));
    }
    return ~crc;
}

unsigned int crc32c(unsigned int crc, const unsigned char* buf, size_t len)
{
    int k;
    crc = ~crc;
    while (len--)
    {
        crc ^= *buf++;
        for (k = 0; k < 8; k++)
            crc = (crc >> 1) ^ (0x82f63b78 & (0 - (crc & 1)));
    }
    return ~crc;
}