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;
  18         float *items; // [n], items[i] = P(pick==i)
  19         float total;
  20 };
  21 #define probdist_total(pd) ((pd)->total)
  22 #define probdist_one(pd, i) ((pd)->items[i])
  23 /* Probability so small that it's same as zero; used to compensate
  24  * for probdist.total inaccuracies. */
  25 #define PROBDIST_EPSILON 0.01
  26
  27 static void probdist_set(struct probdist *pd, int i, float val);
  28
  29 int probdist_pick(struct probdist *pd);
  30
  31
  32 /* We disable the assertions here since this is quite time-critical
  33  * part of code, and also the compiler is reluctant to inline the
  34  * functions otherwise. */
  35 static inline void
  36 probdist_set(struct probdist *pd, int i, float val)
  37 {
  38 #if 0
  39         assert(i >= 0 && i < pd->n);
  40         assert(val >= 0);
  41 #endif
  42         pd->total += val - pd->items[i];
  43         pd->items[i] = val;
  44 }
  45
  46 #endif