crc.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>

uint32_t crc_table[256];

//hash table initialization, call this procedure beforehand we proceed to
//the hashing function
void initTable(void)
{
    uint32_t i = 0;
    int j = 0;

    for (i = 0; i < 256; i++)
    {
        uint32_t c = i;

        for (j = 0; j < 8; j++)
        {
            c = (c & 1) ? (0xEDB88320 ^ (c >> 1)) : (c >> 1);
        }

        crc_table[i] = c;
    }
}

//this function generates the CRC checksum for the string we put in
uint32_t makeCrc(uint8_t *buf, size_t len)
{
    uint32_t c = 0xFFFFFFFF;
    size_t i = 0;

    for (i = 0; i < len; i++)
    {
        c = crc_table[(c ^ buf[i]) & 0xFF] ^ (c >> 8);
    }

    return c ^ 0xFFFFFFFF;
}

int main()
{
    //we initialize the string we want to hash
    const char *crcString = "The quick brown fox jumps over the lazy dog";

    //fill the hash table
    initTable();

    //print out
    printf("CRC hash: %X", makeCrc(crcString, strlen(crcString)));

    return 0;
}