tommath/bn_mp_mul.c
2013-11-24 15:34:41 +01:00

87 lines
2.1 KiB
C

#include <tommath.h>
#ifdef BN_MP_MUL_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* 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.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
/* high level multiplication (handles sign) */
int mp_mul (mp_int * a, mp_int * b, mp_int * c)
{
int res, neg;
neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
int an, bn, tn;
mp_int * t;
an = a -> used;
bn = b -> used;
if (an > bn) {
tn = an; an = bn; bn = tn;
t = a; a = b; b = t;
}
/* now a->used <= b->used */
/* use Toom-Cook? */
#ifdef BN_MP_TOOM_MUL_C
if (a->used >= TOOM_MUL_CUTOFF) {
if (2 * an <= bn) goto balance;
res = mp_toom_mul(a, b, c);
} else
#endif
#ifdef BN_MP_KARATSUBA_MUL_C
/* use Karatsuba? */
if (a->used >= KARATSUBA_MUL_CUTOFF) {
if (2 * an <= bn) goto balance;
res = mp_karatsuba_mul (a, b, c);
} else
#endif
{
/* 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;
#ifdef BN_FAST_S_MP_MUL_DIGS_C
if ((digs < MP_WARRAY) &&
a->used <= (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) {
res = fast_s_mp_mul_digs (a, b, c, digs);
} else
#endif
#ifdef BN_S_MP_MUL_DIGS_C
res = s_mp_mul (a, b, c); /* uses s_mp_mul_digs */
#else
res = MP_VAL;
#endif
}
ret:
c->sign = (c->used > 0) ? neg : MP_ZPOS;
return res;
balance:
/* if a is much smaller than b
* use balance multiplication
* (the idea is taken from Ruby core)
*/
res = mp_balance_mul(a, b, c);
goto ret;
}
#endif
/* $Source$ */
/* $Revision$ */
/* $Date$ */