70 lines
1.5 KiB
C
70 lines
1.5 KiB
C
#include "tommath_private.h"
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#ifdef BN_MP_MUL_2D_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/* shift left by a certain bit count */
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int mp_mul_2d(const mp_int *a, int b, mp_int *c)
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{
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mp_digit d;
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int res;
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/* copy */
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if (a != c) {
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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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}
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if (c->alloc < (c->used + (b / DIGIT_BIT) + 1)) {
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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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}
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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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/* shift any bit count < DIGIT_BIT */
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d = (mp_digit)(b % DIGIT_BIT);
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if (d != 0u) {
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mp_digit *tmpc, shift, mask, r, rr;
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int x;
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/* bitmask for carries */
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mask = ((mp_digit)1 << d) - (mp_digit)1;
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/* shift for msbs */
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shift = (mp_digit)DIGIT_BIT - d;
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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 >> shift) & 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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/* set final carry */
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if (r != 0u) {
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c->dp[(c->used)++] = r;
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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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#endif
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