87 lines
2.1 KiB
C
87 lines
2.1 KiB
C
#include <tommath.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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*
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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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*
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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
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
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*/
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/* high level multiplication (handles sign) */
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int mp_mul (mp_int * a, mp_int * b, mp_int * c)
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{
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int res, neg;
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neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
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int an, bn, tn;
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mp_int * t;
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an = a -> used;
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bn = b -> used;
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if (an > bn) {
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tn = an; an = bn; bn = tn;
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t = a; a = b; b = t;
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}
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/* now a->used <= b->used */
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/* use Toom-Cook? */
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#ifdef BN_MP_TOOM_MUL_C
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if (a->used >= TOOM_MUL_CUTOFF) {
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if (2 * an <= bn) goto balance;
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res = mp_toom_mul(a, b, c);
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} else
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#endif
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#ifdef BN_MP_KARATSUBA_MUL_C
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/* use Karatsuba? */
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if (a->used >= KARATSUBA_MUL_CUTOFF) {
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if (2 * an <= bn) goto balance;
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res = mp_karatsuba_mul (a, b, c);
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} else
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#endif
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{
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/* can we use the fast multiplier?
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*
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* The fast multiplier can be used if the output will
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* have less than MP_WARRAY digits and the number of
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* digits won't affect carry propagation
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*/
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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 < MP_WARRAY) &&
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a->used <= (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) {
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res = fast_s_mp_mul_digs (a, b, c, digs);
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} else
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#endif
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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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}
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ret:
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c->sign = (c->used > 0) ? neg : MP_ZPOS;
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return res;
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balance:
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/* if a is much smaller than b
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* use balance multiplication
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* (the idea is taken from Ruby core)
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*/
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res = mp_balance_mul(a, b, c);
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goto ret;
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}
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#endif
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/* $Source$ */
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/* $Revision$ */
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/* $Date$ */
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