55 lines
1.3 KiB
C
55 lines
1.3 KiB
C
#include "tommath_private.h"
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#ifdef MP_XOR_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 xor */
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mp_err mp_xor(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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bool neg = (a->sign != b->sign);
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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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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 (mp_isneg(a)) {
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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) ? 0uL : a->dp[i];
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}
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/* convert to two complement if negative */
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if (mp_isneg(b)) {
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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) ? 0uL : 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 (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 = (neg ? MP_NEG : MP_ZPOS);
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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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