A simple but usable checksum/hash algorithm, in C.

cyrb32.c

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

unsigned char *data;
int len = 0;

int cyrb32() {
    uint32_t i, tmp, sum = 0xbf3931a8;
    for(i = 32; i < len; i++) {
        sum += (sum << 3) + data[i];
        sum ^= sum >> 1;
    }
    for(tmp = sum; tmp > 0; tmp >>= 3) {
        sum += (sum << 4) ^ tmp;
    }
    return sum;
}

int main() {
    FILE *fp = fopen("lol.note", "rb");
    fseek(fp, 0, SEEK_END);
    len = ftell(fp); 

    rewind(fp);
    data = malloc(len * 8);
    fread(data, len, 1, fp);
    fclose(fp);

    printf("Filesize is: %d bytes\n", len);
    printf("Checksum: %08X\n", cyrb32());
}