probdist.h

   1 #ifndef ZZGO_PROBDIST_H
   2 #define ZZGO_PROBDIST_H
   3
   4 /* Tools for picking an item according to a probability distribution. */
   5
   6 /* The probability distribution structure is designed to be once
   7  * initialized, then random items assigned a value repeatedly and
   8  * random items picked repeatedly as well. */
   9
  10 #include "move.h"
  11 #include "util.h"
  12
  13 /* The interface looks a bit funny-wrapped since we used to switch
  14  * between different probdist representations. */
  15
  16 struct probdist {
  17         int n, n1;
  18         double *items; // [bsize2], [i] = P(pick==i)
  19         double *rowtotals; // [bsize], [i] = sum of items in row i
  20         double total; // sum of all items
  21 };
  22 #define probdist_total(pd) ((pd)->total)
  23 #define probdist_one(pd, c) ((pd)->items[c])
  24 /* Probability so small that it's same as zero; used to compensate
  25  * for probdist.total inaccuracies. */
  26 #define PROBDIST_EPSILON 0.05
  27
  28 static void probdist_set(struct probdist *pd, coord_t c, double val);
  29 static void probdist_mute(struct probdist *pd, coord_t c);
  30
  31 /* Pick a random item. ignore is a pass-terminated sorted array of items
  32  * that are not to be considered (and whose values are not in @total). */
  33 coord_t probdist_pick(struct probdist *pd, coord_t *ignore);
  34
  35
  36 /* We disable the assertions here since this is quite time-critical
  37  * part of code, and also the compiler is reluctant to inline the
  38  * functions otherwise. */
  39 static inline void
  40 probdist_set(struct probdist *pd, coord_t c, double val)
  41 {
  42 #if 0
  43         assert(c >= 0 && c < board_size2(pd->b));
  44         assert(val >= 0);
  45 #endif
  46         pd->total += val - pd->items[c];
  47         pd->rowtotals[c / pd->n1] += val - pd->items[c];
  48         pd->items[c] = val;
  49 }
  50
  51 /* Remove the item from the totals; this is used when you then
  52  * pass it in the ignore list to probdist_pick(). Of course you
  53  * must restore the totals afterwards. */
  54 static inline void
  55 probdist_mute(struct probdist *pd, coord_t c)
  56 {
  57         pd->total -= pd->items[c];
  58         pd->rowtotals[c / pd->n1] -= pd->items[c];
  59 }
  60
  61 #endif