A test program that computes and displays the 64 bit NFW hash of an arbitrary c-string

hash.c

/*
 * This file contains an implementation of the 
 * 64-bit Fowler-Noll-Vo (FNV) hash function.
 *
 * More information can be found here;
 *    http://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
 *
 * Gordon Bailey - Feb 28, 2012
 *
 */

#include <inttypes.h>
#include <stdio.h>

// These values taken from http://isthe.com/chongo/tech/comp/fnv/#FNV-param
const uint64_t FNV_PRIME    = 1099511628211;
const uint64_t OFFSET_BASIS = 14695981039346656037UL;

/* assumes a NULL terminated c-string as input */
uint64_t hash(char * string){
   uint64_t hash = OFFSET_BASIS;
   for(uint8_t * c = (uint8_t*)string; *c != 0; ++c){
      hash ^= *c;
      hash *= FNV_PRIME;
   }
   return hash;
}

/* assumes that outString has space allocated for 16 chars */
void getHex(uint64_t val, char * outString){
   const char chars[] = "0123456789ABCDEF";
   for(int i = 15; i >= 0; --i){
      outString[i] = chars[val&15];
      val >>= 4;
   }
   // add null terminator
   outString[16] = '\0';
}

int main(int argc, const char *argv[])
{
   // hold the outputted hex string
   char hexString[17];
   // copy entire argv into a single string (seperating elements with spaces)
   char string[1024];
   int j = 0;
   for(int i = 1; i < argc; ++i){
      for(const char * c = argv[i]; *c != '\0'; ++c){
         if(j == 1023) break;
         string[j] = *c;
         ++j;
      }
      if(j == 1023) break;
      string[j] = ' ';
      ++j;
   }
   string[j] = '\0';

   // get the hex string and print it.
   uint64_t h = hash(string);
   getHex(h, hexString);
   printf("%s\n", string);
   printf("%s\n", hexString);
   return 0;
}