tommath/bn_mp_mul.c

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#include "tommath_private.h"
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#ifdef BN_MP_MUL_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*/
/* high level multiplication (handles sign) */
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int mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
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{
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int res, neg;
neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
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/* use Toom-Cook? */
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#ifdef BN_MP_TOOM_MUL_C
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if (MIN(a->used, b->used) >= TOOM_MUL_CUTOFF) {
res = mp_toom_mul(a, b, c);
} else
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#endif
#ifdef BN_MP_KARATSUBA_MUL_C
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/* use Karatsuba? */
if (MIN(a->used, b->used) >= KARATSUBA_MUL_CUTOFF) {
res = mp_karatsuba_mul(a, b, c);
} else
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#endif
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{
/* can we use the fast multiplier?
*
* The fast multiplier can be used if the output will
* have less than MP_WARRAY digits and the number of
* digits won't affect carry propagation
*/
int digs = a->used + b->used + 1;
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#ifdef BN_FAST_S_MP_MUL_DIGS_C
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if ((digs < (int)MP_WARRAY) &&
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(MIN(a->used, b->used) <=
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(int)(1u << (((size_t)CHAR_BIT * sizeof(mp_word)) - (2u * (size_t)DIGIT_BIT))))) {
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res = fast_s_mp_mul_digs(a, b, c, digs);
} else
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#endif
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{
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#ifdef BN_S_MP_MUL_DIGS_C
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res = s_mp_mul(a, b, c); /* uses s_mp_mul_digs */
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#else
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res = MP_VAL;
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#endif
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}
}
c->sign = (c->used > 0) ? neg : MP_ZPOS;
return res;
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}
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#endif
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/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */