mp_rand.c

   1 #include "tommath_private.h"
   2 #ifdef MP_RAND_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
   4 /* SPDX-License-Identifier: Unlicense */
   5
   6 mp_err mp_rand(mp_int *a, int digits)
   7 {
   8    int i;
   9    mp_err err;
  10
  11    mp_zero(a);
  12
  13    if (digits <= 0) {
  14       return MP_OKAY;
  15    }
  16
  17    if ((err = mp_grow(a, digits)) != MP_OKAY) {
  18       return err;
  19    }
  20
  21    if ((err = s_mp_rand_source(a->dp, (size_t)digits * sizeof(mp_digit))) != MP_OKAY) {
  22       return err;
  23    }
  24
  25    /* TODO: We ensure that the highest digit is nonzero. Should this be removed? */
  26    while ((a->dp[digits - 1] & MP_MASK) == 0u) {
  27       if ((err = s_mp_rand_source(a->dp + digits - 1, sizeof(mp_digit))) != MP_OKAY) {
  28          return err;
  29       }
  30    }
  31
  32    a->used = digits;
  33    for (i = 0; i < digits; ++i) {
  34       a->dp[i] &= MP_MASK;
  35    }
  36
  37    return MP_OKAY;
  38 }
  39 #endif