calcest.c

   1 #include <stdio.h>
   2 #include <stddef.h>
   3 #include <math.h>
   4
   5 /*
   6  * as per scribblemaniac's explanation:
   7  * t - number of trials
   8  * n - character count
   9  * p - probability
  10  * condition: >=1 matches
  11  * formula: t = log(1-p)/log(1-1/32^n)
  12  * comes from:
  13  *  distribution X~Binomial(t, 1/32^n)
  14  *  P(X>=1)=p
  15  */
  16
  17 const double probs[] = { 0.5, 0.8, 0.9, 0.95, 0.99 };
  18 const int charcounts[] = { 2, 3, 4, 5, 6, 7 };
  19
  20 int main(void)
  21 {
  22         printf("   |");
  23         for (size_t i = 0; i < sizeof(probs)/sizeof(probs[0]); ++i) {
  24                 printf(" %11d%% |",(int)((probs[i]*100)+0.5));
  25         }
  26         printf("\n");
  27
  28         printf("---+");
  29         for (size_t i = 0; i < sizeof(probs)/sizeof(probs[0]); ++i) {
  30                 printf("--------------+");
  31         }
  32         printf("\n");
  33
  34         for (size_t i = 0; i < sizeof(charcounts)/sizeof(charcounts[0]); ++i) {
  35                 printf("%2d |",charcounts[i]);
  36                 for (size_t j = 0; j < sizeof(probs)/sizeof(probs[0]); ++j) {
  37                         double t = log2(1 - probs[j]) / log2(1 - (1 / pow(32,charcounts[i])));
  38                         printf(" %12.0f |",t);
  39                 }
  40                 printf("\n");
  41         }
  42
  43         return 0;
  44 }