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"
|
|
#ifdef BN_MP_XOR_C
|
|
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
|
|
/* SPDX-License-Identifier: Unlicense */
|
|
|
|
/* two complement xor */
|
|
mp_err mp_xor(const mp_int *a, const mp_int *b, mp_int *c)
|
|
{
|
|
int used = MP_MAX(a->used, b->used) + 1, i;
|
|
mp_err err;
|
|
mp_digit ac = 1, bc = 1, cc = 1;
|
|
mp_sign csign = (a->sign != b->sign) ? MP_NEG : MP_ZPOS;
|
|
|
|
if (c->alloc < used) {
|
|
if ((err = mp_grow(c, used)) != MP_OKAY) {
|
|
return err;
|
|
}
|
|
}
|
|
|
|
for (i = 0; i < used; i++) {
|
|
mp_digit x, y;
|
|
|
|
/* convert to two complement if negative */
|
|
if (a->sign == MP_NEG) {
|
|
ac += i >= a->used ? MP_MASK : ~a->dp[i] & MP_MASK;
|
|
x = ac & MP_MASK;
|
|
ac >>= MP_DIGIT_BIT;
|
|
} else {
|
|
x = i >= a->used ? 0 : a->dp[i];
|
|
}
|
|
|
|
/* convert to two complement if negative */
|
|
if (b->sign == MP_NEG) {
|
|
bc += i >= b->used ? MP_MASK : ~b->dp[i] & MP_MASK;
|
|
y = bc & MP_MASK;
|
|
bc >>= MP_DIGIT_BIT;
|
|
} else {
|
|
y = i >= b->used ? 0 : b->dp[i];
|
|
}
|
|
|
|
c->dp[i] = x ^ y;
|
|
|
|
/* convert to to sign-magnitude if negative */
|
|
if (csign == MP_NEG) {
|
|
cc += ~c->dp[i] & MP_MASK;
|
|
c->dp[i] = cc & MP_MASK;
|
|
cc >>= MP_DIGIT_BIT;
|
|
}
|
|
}
|
|
|
|
c->used = used;
|
|
c->sign = csign;
|
|
mp_clamp(c);
|
|
return MP_OKAY;
|
|
}
|
|
#endif
|