55 lines
1.3 KiB
C
55 lines
1.3 KiB
C
#include "tommath_private.h"
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#ifdef MP_MUL_D_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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/* multiply by a digit */
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mp_err mp_mul_d(const mp_int *a, mp_digit b, mp_int *c)
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{
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mp_digit u;
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mp_err err;
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int ix, oldused;
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/* make sure c is big enough to hold a*b */
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if (c->alloc < (a->used + 1)) {
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if ((err = mp_grow(c, a->used + 1)) != MP_OKAY) {
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return err;
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}
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}
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/* get the original destinations used count */
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oldused = c->used;
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/* set the sign */
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c->sign = a->sign;
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/* zero carry */
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u = 0;
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/* compute columns */
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for (ix = 0; ix < a->used; ix++) {
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/* compute product and carry sum for this term */
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mp_word r = (mp_word)u + ((mp_word)a->dp[ix] * (mp_word)b);
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/* mask off higher bits to get a single digit */
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c->dp[ix] = (mp_digit)(r & (mp_word)MP_MASK);
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/* send carry into next iteration */
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u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
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}
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/* store final carry [if any] and increment ix offset */
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c->dp[ix] = u;
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/* set used count */
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c->used = a->used + 1;
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/* now zero digits above the top */
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MP_ZERO_DIGITS(c->dp + c->used, oldused - c->used);
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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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