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 #include "board.h"
  10
  11 coord_t
  12 probdist_pick(struct probdist *pd, coord_t *ignore)
  13 {
  14         double total = probdist_total(pd) - PROBDIST_EPSILON;
  15         assert(total >= 0);
  16         double stab = fast_frandom() * total;
  17         //fprintf(stderr, "stab %f / %f\n", stab, total);
  18
  19         int r = 0;
  20         while (stab > pd->rowtotals[r] + PROBDIST_EPSILON) {
  21                 stab -= pd->rowtotals[r];
  22                 r++;
  23                 assert(r < board_size(pd->b));
  24         }
  25         for (coord_t c = r * board_size(pd->b); c < board_size2(pd->b); c++) {
  26                 //fprintf(stderr, "[%s] %f (%f)\n", coord2sstr(c, &pd->b), pd->items[c], stab);
  27                 if (c == *ignore) {
  28                         ignore++;
  29                         continue;
  30                 }
  31                 if (stab <= pd->items[c])
  32                         return c;
  33                 stab -= pd->items[c];
  34         }
  35
  36         fprintf(stderr, "overstab %f (total %f)\n", stab, total);
  37         assert(0);
  38         return -1;
  39 }