3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
12 * The library is free for all purposes without any express
15 * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
18 /* high level multiplication (handles sign) */
19 int mp_mul (mp_int * a, mp_int * b, mp_int * c)
22 neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
25 #ifdef BN_MP_TOOM_MUL_C
26 if (MIN (a->used, b->used) >= TOOM_MUL_CUTOFF) {
27 res = mp_toom_mul(a, b, c);
30 #ifdef BN_MP_KARATSUBA_MUL_C
32 if (MIN (a->used, b->used) >= KARATSUBA_MUL_CUTOFF) {
33 res = mp_karatsuba_mul (a, b, c);
37 /* can we use the fast multiplier?
39 * The fast multiplier can be used if the output will
40 * have less than MP_WARRAY digits and the number of
41 * digits won't affect carry propagation
43 int digs = a->used + b->used + 1;
45 #ifdef BN_FAST_S_MP_MUL_DIGS_C
46 if ((digs < MP_WARRAY) &&
47 MIN(a->used, b->used) <=
48 (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) {
49 res = fast_s_mp_mul_digs (a, b, c, digs);
52 #ifdef BN_S_MP_MUL_DIGS_C
53 res = s_mp_mul (a, b, c); /* uses s_mp_mul_digs */
59 c->sign = (c->used > 0) ? neg : MP_ZPOS;