45 lines
1.3 KiB
C
45 lines
1.3 KiB
C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is library that provides for multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library is 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@iahu.ca, http://libtommath.iahu.ca
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*/
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#include <tommath.h>
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/* high level multiplication (handles sign) */
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int
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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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if (MIN (a->used, b->used) > KARATSUBA_MUL_CUTOFF) {
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res = mp_karatsuba_mul (a, b, c);
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} else {
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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 have less than
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* 512 digits and the number of 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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if ((digs < 512)
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&& digs < (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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res = s_mp_mul (a, b, c);
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}
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}
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c->sign = neg;
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return res;
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}
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