mp_reduce_2k_setup.c

   1 #include "tommath_private.h"
   2 #ifdef MP_REDUCE_2K_SETUP_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
   4 /* SPDX-License-Identifier: Unlicense */
   5
   6 /* determines the setup value */
   7 mp_err mp_reduce_2k_setup(const mp_int *a, mp_digit *d)
   8 {
   9    mp_err err;
  10    mp_int tmp;
  11
  12    if ((err = mp_init(&tmp)) != MP_OKAY) {
  13       return err;
  14    }
  15
  16    if ((err = mp_2expt(&tmp, mp_count_bits(a))) != MP_OKAY) {
  17       goto LBL_ERR;
  18    }
  19
  20    if ((err = s_mp_sub(&tmp, a, &tmp)) != MP_OKAY) {
  21       goto LBL_ERR;
  22    }
  23
  24    *d = tmp.dp[0];
  25
  26 LBL_ERR:
  27    mp_clear(&tmp);
  28    return err;
  29 }
  30 #endif