1af0de1f91
* same behavior for positive numbers * generalisation for negative numbers, treating them as two complement * improve algorithm, iterate once over the digits, manually perform two complement * simplify mp_add_d, mp_sub_d * functions are safe in case of a==c or b==c * renamed mp_tc_div_2d to mp_signed_rsh (signed right shift)
57 lines
1.4 KiB
C
57 lines
1.4 KiB
C
#include "tommath_private.h"
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#ifdef BN_MP_AND_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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/* two complement and */
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mp_err mp_and(const mp_int *a, const mp_int *b, mp_int *c)
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{
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int used = MP_MAX(a->used, b->used) + 1, i;
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mp_err err;
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mp_digit ac = 1, bc = 1, cc = 1;
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mp_sign csign = (a->sign == MP_NEG && b->sign == MP_NEG) ? MP_NEG : MP_ZPOS;
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if (c->alloc < used) {
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if ((err = mp_grow(c, used)) != MP_OKAY) {
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return err;
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}
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}
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for (i = 0; i < used; i++) {
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mp_digit x, y;
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/* convert to two complement if negative */
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if (a->sign == MP_NEG) {
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ac += i >= a->used ? MP_MASK : ~a->dp[i] & MP_MASK;
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x = ac & MP_MASK;
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ac >>= MP_DIGIT_BIT;
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} else {
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x = i >= a->used ? 0 : a->dp[i];
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}
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/* convert to two complement if negative */
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if (b->sign == MP_NEG) {
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bc += i >= b->used ? MP_MASK : ~b->dp[i] & MP_MASK;
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y = bc & MP_MASK;
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bc >>= MP_DIGIT_BIT;
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} else {
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y = i >= b->used ? 0 : b->dp[i];
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}
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c->dp[i] = x & y;
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/* convert to to sign-magnitude if negative */
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if (csign == MP_NEG) {
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cc += ~c->dp[i] & MP_MASK;
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c->dp[i] = cc & MP_MASK;
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cc >>= MP_DIGIT_BIT;
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}
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}
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c->used = used;
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c->sign = csign;
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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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