Line data    Source code

       1             : #include "tommath_private.h"
       2             : #ifdef BN_MP_MUL_C
       3             : /* LibTomMath, multiple-precision integer library -- Tom St Denis */
       4             : /* SPDX-License-Identifier: Unlicense */
       5             : 
       6             : /* high level multiplication (handles sign) */
       7      120283 : mp_err mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
       8             : {
       9        5280 :    mp_err err;
      10      120283 :    int min_len = MP_MIN(a->used, b->used),
      11      120283 :        max_len = MP_MAX(a->used, b->used),
      12      120283 :        digs = a->used + b->used + 1;
      13      120283 :    mp_sign neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
      14             : 
      15      120283 :    if (MP_HAS(S_MP_BALANCE_MUL) &&
      16             :        /* Check sizes. The smaller one needs to be larger than the Karatsuba cut-off.
      17             :         * The bigger one needs to be at least about one MP_KARATSUBA_MUL_CUTOFF bigger
      18             :         * to make some sense, but it depends on architecture, OS, position of the
      19             :         * stars... so YMMV.
      20             :         * Using it to cut the input into slices small enough for fast_s_mp_mul_digs
      21             :         * was actually slower on the author's machine, but YMMV.
      22             :         */
      23         906 :        (min_len >= MP_KARATSUBA_MUL_CUTOFF) &&
      24         906 :        ((max_len / 2) >= MP_KARATSUBA_MUL_CUTOFF) &&
      25             :        /* Not much effect was observed below a ratio of 1:2, but again: YMMV. */
      26           0 :        (max_len >= (2 * min_len))) {
      27           0 :       err = s_mp_balance_mul(a,b,c);
      28      120283 :    } else if (MP_HAS(S_MP_TOOM_MUL) &&
      29             :               (min_len >= MP_TOOM_MUL_CUTOFF)) {
      30           0 :       err = s_mp_toom_mul(a, b, c);
      31      120283 :    } else if (MP_HAS(S_MP_KARATSUBA_MUL) &&
      32             :               (min_len >= MP_KARATSUBA_MUL_CUTOFF)) {
      33         906 :       err = s_mp_karatsuba_mul(a, b, c);
      34      119377 :    } else if (MP_HAS(S_MP_MUL_DIGS_FAST) &&
      35             :               /* can we use the fast multiplier?
      36             :                *
      37             :                * The fast multiplier can be used if the output will
      38             :                * have less than MP_WARRAY digits and the number of
      39             :                * digits won't affect carry propagation
      40             :                */
      41      119377 :               (digs < MP_WARRAY) &&
      42        5280 :               (min_len <= MP_MAXFAST)) {
      43      119377 :       err = s_mp_mul_digs_fast(a, b, c, digs);
      44           0 :    } else if (MP_HAS(S_MP_MUL_DIGS)) {
      45           0 :       err = s_mp_mul_digs(a, b, c, digs);
      46             :    } else {
      47             :       err = MP_VAL;
      48             :    }
      49      120283 :    c->sign = (c->used > 0) ? neg : MP_ZPOS;
      50      120283 :    return err;
      51             : }
      52             : #endif