crc_fnv_fiasco.c

// For a fully compiled version look at https://gist.github.com/danlark1/69c9d5e1d356eaa32dbdfccb2e19f401
#include <stdint.h>
#include <stddef.h>
#include <stdio.h>

#define FNV32INIT 2166136261U
#define FNV32PRIME 16777619U
#define FNV64INIT 14695981039346656037ULL
#define FNV64PRIME 1099511628211ULL

// Any table
extern unsigned long crc64table[256];

unsigned long fnv64(const void *p, size_t len) {
  unsigned long init = FNV64INIT;
  const unsigned char *_p = (const unsigned char *)p;
  for (size_t i = 0; i < len; ++i) {
    init = (init * FNV64PRIME) ^ _p[i];
  }
  return init;
}

unsigned long crc64(unsigned long crc, const void *p, size_t len) {
  size_t i, t;
  const unsigned char *_p = (const unsigned char *)p;
  for (i = 0; i < len; i++) {
    t = ((crc >> 56) ^ (*_p++)) & 0xFF;
    crc = crc64table[t] ^ (crc << 8);
  }
  return crc;
}

int main() {
  const char* data1 = "l.im/8ca";
  const char* data2 = "l.im/8cf";
  size_t size = 8;
  unsigned long crc = crc64(fnv64(data1, size), data1, size);
  printf("%lu\n", crc); // 6193082687915471267
  crc = crc64(fnv64(data2, size), data2, size);
  printf("%lu\n", crc); // 6193082687915471267
}