69 lines
1.6 KiB
C
69 lines
1.6 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://math.libtomcrypt.org
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*/
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#include <tommath.h>
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/* shift left by a certain bit count */
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int
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mp_mul_2d (mp_int * a, int b, mp_int * c)
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{
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mp_digit d, r, rr;
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int x, res;
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/* copy */
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if ((res = mp_copy (a, c)) != MP_OKAY) {
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return res;
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}
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if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) {
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return res;
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}
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/* shift by as many digits in the bit count */
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if (b >= DIGIT_BIT) {
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if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
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return res;
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}
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}
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c->used = c->alloc;
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/* shift any bit count < DIGIT_BIT */
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d = (mp_digit) (b % DIGIT_BIT);
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if (d != 0) {
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register mp_digit *tmpc, mask;
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/* bitmask for carries */
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mask = (1U << d) - 1U;
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/* alias */
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tmpc = c->dp;
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/* carry */
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r = 0;
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for (x = 0; x < c->used; x++) {
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/* get the higher bits of the current word */
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rr = (*tmpc >> (DIGIT_BIT - d)) & mask;
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/* shift the current word and OR in the carry */
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*tmpc = ((*tmpc << d) | r) & MP_MASK;
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++tmpc;
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/* set the carry to the carry bits of the current word */
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r = rr;
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}
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}
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mp_clamp (c);
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return MP_OKAY;
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}
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