Viewing file:  bn_add.c (3.35 KB) -rw-r--r--
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/*
* Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include "internal/cryptlib.h"
#include "bn_local.h"
/* signed add of b to a. */
int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
{
int ret, r_neg, cmp_res;
bn_check_top(a);
bn_check_top(b);
if (a->neg == b->neg) {
r_neg = a->neg;
ret = BN_uadd(r, a, b);
} else {
cmp_res = BN_ucmp(a, b);
if (cmp_res > 0) {
r_neg = a->neg;
ret = BN_usub(r, a, b);
} else if (cmp_res < 0) {
r_neg = b->neg;
ret = BN_usub(r, b, a);
} else {
r_neg = 0;
BN_zero(r);
ret = 1;
}
}
r->neg = r_neg;
bn_check_top(r);
return ret;
}
/* signed sub of b from a. */
int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
{
int ret, r_neg, cmp_res;
bn_check_top(a);
bn_check_top(b);
if (a->neg != b->neg) {
r_neg = a->neg;
ret = BN_uadd(r, a, b);
} else {
cmp_res = BN_ucmp(a, b);
if (cmp_res > 0) {
r_neg = a->neg;
ret = BN_usub(r, a, b);
} else if (cmp_res < 0) {
r_neg = !b->neg;
ret = BN_usub(r, b, a);
} else {
r_neg = 0;
BN_zero(r);
ret = 1;
}
}
r->neg = r_neg;
bn_check_top(r);
return ret;
}
/* unsigned add of b to a, r can be equal to a or b. */
int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
{
int max, min, dif;
const BN_ULONG *ap, *bp;
BN_ULONG *rp, carry, t1, t2;
bn_check_top(a);
bn_check_top(b);
if (a->top < b->top) {
const BIGNUM *tmp;
tmp = a;
a = b;
b = tmp;
}
max = a->top;
min = b->top;
dif = max - min;
if (bn_wexpand(r, max + 1) == NULL)
return 0;
r->top = max;
ap = a->d;
bp = b->d;
rp = r->d;
carry = bn_add_words(rp, ap, bp, min);
rp += min;
ap += min;
while (dif) {
dif--;
t1 = *(ap++);
t2 = (t1 + carry) & BN_MASK2;
*(rp++) = t2;
carry &= (t2 == 0);
}
*rp = carry;
r->top += carry;
r->neg = 0;
bn_check_top(r);
return 1;
}
/* unsigned subtraction of b from a, a must be larger than b. */
int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
{
int max, min, dif;
BN_ULONG t1, t2, borrow, *rp;
const BN_ULONG *ap, *bp;
bn_check_top(a);
bn_check_top(b);
max = a->top;
min = b->top;
dif = max - min;
if (dif < 0) { /* hmm... should not be happening */
ERR_raise(ERR_LIB_BN, BN_R_ARG2_LT_ARG3);
return 0;
}
if (bn_wexpand(r, max) == NULL)
return 0;
ap = a->d;
bp = b->d;
rp = r->d;
borrow = bn_sub_words(rp, ap, bp, min);
ap += min;
rp += min;
while (dif) {
dif--;
t1 = *(ap++);
t2 = (t1 - borrow) & BN_MASK2;
*(rp++) = t2;
borrow &= (t1 == 0);
}
while (max && *--rp == 0)
max--;
r->top = max;
r->neg = 0;
bn_pollute(r);
return 1;
}
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