64 lines
1.4 KiB
C
64 lines
1.4 KiB
C
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#include "tommath_private.h"
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#ifdef 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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mp_err mp_mul_2d(const mp_int *a, int b, mp_int *c)
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{
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mp_err err;
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if (b < 0) {
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return MP_VAL;
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}
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if ((err = mp_copy(a, c)) != MP_OKAY) {
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return err;
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}
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if ((err = mp_grow(c, c->used + (b / MP_DIGIT_BIT) + 1)) != MP_OKAY) {
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return err;
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}
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/* shift by as many digits in the bit count */
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if (b >= MP_DIGIT_BIT) {
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if ((err = mp_lshd(c, b / MP_DIGIT_BIT)) != MP_OKAY) {
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return err;
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}
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}
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/* shift any bit count < MP_DIGIT_BIT */
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b %= MP_DIGIT_BIT;
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if (b != 0u) {
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mp_digit shift, mask, r;
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int x;
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/* bitmask for carries */
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mask = ((mp_digit)1 << b) - (mp_digit)1;
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/* shift for msbs */
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shift = (mp_digit)(MP_DIGIT_BIT - b);
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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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mp_digit rr = (c->dp[x] >> shift) & mask;
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/* shift the current word and OR in the carry */
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c->dp[x] = ((c->dp[x] << b) | r) & MP_MASK;
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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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