/* Test hash function for hex.c

   Currently the colors assigned using a table of random numbers that is
   looked up using coordinates, but we ought to be able to just hash
   those coordinate values into random values.  This file tests what
   kind of color distributions we would get out of using hash functions.
                                                                         */

#include<assert.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<time.h>

#define INPUT_RANGE     20
#define OUTPUT_BUCKETS  4

static int use_rand = 0;

/* https://en.wikipedia.org/wiki/Jenkins_hash_function */
static int OneAtATimeHash(int key, int r, int q)
{
   int i, h;

   key ^= (r & 0xff) ^ ((q & 0xff) << 8);
   for(i = h = 0; i < 4; i++)
   {
      h += (key >> (i * 8)) & 0xff;
      h += h << 10;
      h ^= h >> 6;
   }

   h += h << 3;
   h ^= h >> 11;
   h += h << 15;
   return h & 3;
}

int main(void)
{
   int count[OUTPUT_BUCKETS], r, q, h;
   int key = time(NULL);

   srand(key);

   memset(count, 0, sizeof(count));
   for(r = -INPUT_RANGE; r <= INPUT_RANGE; r++)
   {
      for(q = -INPUT_RANGE; q <= INPUT_RANGE; q++)
      {
         if( use_rand )
         {
            h = (int)((double)rand() / RAND_MAX * 4.0);
         }
         else
         {
            h = OneAtATimeHash(key, r, q);
         }
         printf("\x1b[30;%dm%d", h + 101, h);
         assert(h >= 0);
         assert(h < OUTPUT_BUCKETS);
         count[h]++;
      }
      puts("\x1b[0m");
   }

   for(h = 0; h < OUTPUT_BUCKETS; h++)
      printf("h[%d] = %d\n", h, count[h]);
   return 0;
}