50 lines
1.0 KiB
C
50 lines
1.0 KiB
C
#include "tommath_private.h"
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#ifdef BN_MP_DIV_2_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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/* b = a/2 */
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mp_err mp_div_2(const mp_int *a, mp_int *b)
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{
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int x, oldused;
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mp_digit r, rr, *tmpa, *tmpb;
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mp_err err;
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/* copy */
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if (b->alloc < a->used) {
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if ((err = mp_grow(b, a->used)) != MP_OKAY) {
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return err;
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}
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}
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oldused = b->used;
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b->used = a->used;
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/* source alias */
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tmpa = a->dp + b->used - 1;
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/* dest alias */
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tmpb = b->dp + b->used - 1;
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/* carry */
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r = 0;
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for (x = b->used - 1; x >= 0; x--) {
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/* get the carry for the next iteration */
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rr = *tmpa & 1u;
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/* shift the current digit, add in carry and store */
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*tmpb-- = (*tmpa-- >> 1) | (r << (MP_DIGIT_BIT - 1));
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/* forward carry to next iteration */
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r = rr;
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}
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/* zero excess digits */
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MP_ZERO_DIGITS(b->dp + b->used, oldused - b->used);
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b->sign = a->sign;
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mp_clamp(b);
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return MP_OKAY;
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}
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#endif
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