libtommath/mp_prime_rabin_miller_trials.c

#include "tommath_private.h"
#ifdef MP_PRIME_RABIN_MILLER_TRIALS_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

static const struct {
   int k, t;
} sizes[] = {
   {    80, -1 }, /* Use deterministic algorithm for size <= 80 bits */
   {    81, 37 }, /* max. error = 2^(-96)*/
   {    96, 32 }, /* max. error = 2^(-96)*/
   {   128, 40 }, /* max. error = 2^(-112)*/
   {   160, 35 }, /* max. error = 2^(-112)*/
   {   256, 27 }, /* max. error = 2^(-128)*/
   {   384, 16 }, /* max. error = 2^(-128)*/
   {   512, 18 }, /* max. error = 2^(-160)*/
   {   768, 11 }, /* max. error = 2^(-160)*/
   {   896, 10 }, /* max. error = 2^(-160)*/
   {  1024, 12 }, /* max. error = 2^(-192)*/
   {  1536, 8  }, /* max. error = 2^(-192)*/
   {  2048, 6  }, /* max. error = 2^(-192)*/
   {  3072, 4  }, /* max. error = 2^(-192)*/
   {  4096, 5  }, /* max. error = 2^(-256)*/
   {  5120, 4  }, /* max. error = 2^(-256)*/
   {  6144, 4  }, /* max. error = 2^(-256)*/
   {  8192, 3  }, /* max. error = 2^(-256)*/
   {  9216, 3  }, /* max. error = 2^(-256)*/
   { 10240, 2  }  /* For bigger keysizes use always at least 2 Rounds */
};

/* returns # of RM trials required for a given bit size */
int mp_prime_rabin_miller_trials(int size)
{
   int x;

   for (x = 0; x < (int)(sizeof(sizes)/(sizeof(sizes[0]))); x++) {
      if (sizes[x].k == size) {
         return sizes[x].t;
      }
      if (sizes[x].k > size) {
         return (x == 0) ? sizes[0].t : sizes[x - 1].t;
      }
   }
   return sizes[x-1].t;
}


#endif