probdist.c

   1 #include <assert.h>
   2 #include <math.h>
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5
   6 //#define DEBUG
   7 #include "debug.h"
   8 #include "move.h"
   9 #include "probdist.h"
  10 #include "random.h"
  11 #include "board.h"
  12
  13 coord_t
  14 probdist_pick(struct probdist *pd, coord_t *ignore)
  15 {
  16         double total = probdist_total(pd) - PROBDIST_EPSILON;
  17         assert(total >= 0);
  18         double stab = fast_frandom() * total;
  19         if (DEBUGL(6))
  20                 fprintf(stderr, "stab %f / %f\n", stab, total);
  21
  22         int r = 0;
  23         while (stab > pd->rowtotals[r] + PROBDIST_EPSILON) {
  24                 stab -= pd->rowtotals[r];
  25                 r++;
  26                 assert(r < board_size(pd->b));
  27         }
  28         for (coord_t c = r * board_size(pd->b); c < board_size2(pd->b); c++) {
  29                 if (DEBUGL(6))
  30                         fprintf(stderr, "[%s] %f (%f)\n", coord2sstr(c, pd->b), pd->items[c], stab);
  31                 if (c == *ignore) {
  32                         ignore++;
  33                         continue;
  34                 }
  35                 if (stab <= pd->items[c])
  36                         return c;
  37                 stab -= pd->items[c];
  38         }
  39
  40         fprintf(stderr, "overstab %f (total %f)\n", stab, total);
  41         assert(0);
  42         return -1;
  43 }