probdist.c

   1 #include <assert.h>
   2 #include <math.h>
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5
   6 #include "move.h"
   7 #include "probdist.h"
   8 #include "random.h"
   9
  10 struct probdist *
  11 probdist_init(struct probdist *pd, int n)
  12 {
  13         if (!pd) pd = malloc(sizeof(*pd));
  14         pd->n = n;
  15         pd->items = calloc(n, sizeof(pd->items[0]));
  16         pd->total = 0;
  17         return pd;
  18 }
  19
  20 coord_t
  21 probdist_pick(struct probdist *pd)
  22 {
  23         assert(pd->total > -1); // -1..0 is rounding error
  24         if (pd->total < __FLT_EPSILON__)
  25                 return pass;
  26         float stab = (float) fast_random(65536) / 65536 * pd->total;
  27         float sum = 0;
  28         //fprintf(stderr, "stab %f / %f\n", stab, pd->total);
  29         for (int i = 0; i < pd->n; i++) {
  30                 sum += pd->items[i];
  31                 if (stab < sum)
  32                         return i;
  33         }
  34         //fprintf(stderr, "overstab %f (total %f, sum %f)\n", stab, pd->total, sum);
  35         // This can sometimes happen when also punching due to rounding errors,.
  36         // Just assert that the difference is tiny.
  37         assert(fabs(pd->total - stab) < 1);
  38         return pass;
  39 }
  40
  41 void
  42 probdist_done(struct probdist *pd) {
  43         free(pd->items);
  44 }