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bn/bn_add.c: favour counted loops over ifs and breaks.

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Reviewed-by: Rich Salz <rsalz@openssl.org>
This commit is contained in:
Andy Polyakov 2016-06-12 12:34:46 +02:00
parent 2ac68bd6f1
commit 7d6284057b
1 changed files with 37 additions and 71 deletions
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108
crypto/bn/bn_add.c
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@ -13,7 +13,6 @@
/* r can == a or b */ /* r can == a or b */
int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
{ {
const BIGNUM *tmp;
int a_neg = a->neg, ret; int a_neg = a->neg, ret;
bn_check_top(a); bn_check_top(a);
@ -28,6 +27,8 @@ int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
if (a_neg ^ b->neg) { if (a_neg ^ b->neg) {
/* only one is negative */ /* only one is negative */
if (a_neg) { if (a_neg) {
const BIGNUM *tmp;
tmp = a; tmp = a;
a = b; a = b;
b = tmp; b = tmp;
@ -37,14 +38,14 @@ int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
if (BN_ucmp(a, b) < 0) { if (BN_ucmp(a, b) < 0) {
if (!BN_usub(r, b, a)) if (!BN_usub(r, b, a))
return (0); return 0;
r->neg = 1; r->neg = 1;
} else { } else {
if (!BN_usub(r, a, b)) if (!BN_usub(r, a, b))
return (0); return 0;
r->neg = 0; r->neg = 0;
} }
return (1); return 1;
} }
ret = BN_uadd(r, a, b); ret = BN_uadd(r, a, b);
@ -59,12 +60,13 @@ int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
int max, min, dif; int max, min, dif;
const BN_ULONG *ap, *bp; const BN_ULONG *ap, *bp;
BN_ULONG *rp, carry, t1, t2; BN_ULONG *rp, carry, t1, t2;
const BIGNUM *tmp;
bn_check_top(a); bn_check_top(a);
bn_check_top(b); bn_check_top(b);
if (a->top < b->top) { if (a->top < b->top) {
const BIGNUM *tmp;
tmp = a; tmp = a;
a = b; a = b;
b = tmp; b = tmp;
@ -85,29 +87,17 @@ int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
carry = bn_add_words(rp, ap, bp, min); carry = bn_add_words(rp, ap, bp, min);
rp += min; rp += min;
ap += min; ap += min;
bp += min;
if (carry) { while (dif) {
while (dif) { dif--;
dif--; t1 = *(ap++);
t1 = *(ap++); t2 = (t1 + carry) & BN_MASK2;
t2 = (t1 + 1) & BN_MASK2; *(rp++) = t2;
*(rp++) = t2; carry &= (t2 == 0);
if (t2) {
carry = 0;
break;
}
}
if (carry) {
/* carry != 0 => dif == 0 */
*rp = 1;
r->top++;
}
} }
if (dif && rp != ap) *rp = carry;
while (dif--) r->top += carry;
/* copy remaining words if ap != rp */
*(rp++) = *(ap++);
r->neg = 0; r->neg = 0;
bn_check_top(r); bn_check_top(r);
return 1; return 1;
@ -117,9 +107,8 @@ int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
{ {
int max, min, dif; int max, min, dif;
register BN_ULONG t1, t2, *rp; BN_ULONG t1, t2, borrow, *rp;
register const BN_ULONG *ap, *bp; const BN_ULONG *ap, *bp;
int i, carry;
bn_check_top(a); bn_check_top(a);
bn_check_top(b); bn_check_top(b);
@ -130,63 +119,38 @@ int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
if (dif < 0) { /* hmm... should not be happening */ if (dif < 0) { /* hmm... should not be happening */
BNerr(BN_F_BN_USUB, BN_R_ARG2_LT_ARG3); BNerr(BN_F_BN_USUB, BN_R_ARG2_LT_ARG3);
return (0); return 0;
} }
if (bn_wexpand(r, max) == NULL) if (bn_wexpand(r, max) == NULL)
return (0); return 0;
ap = a->d; ap = a->d;
bp = b->d; bp = b->d;
rp = r->d; rp = r->d;
#if 1 borrow = bn_sub_words(rp, ap, bp, min);
carry = 0;
for (i = min; i != 0; i--) {
t1 = *(ap++);
t2 = *(bp++);
if (carry) {
carry = (t1 <= t2);
t1 = (t1 - t2 - 1) & BN_MASK2;
} else {
carry = (t1 < t2);
t1 = (t1 - t2) & BN_MASK2;
}
*(rp++) = t1 & BN_MASK2;
}
#else
carry = bn_sub_words(rp, ap, bp, min);
ap += min; ap += min;
bp += min;
rp += min; rp += min;
#endif
if (carry) { /* subtracted */ while (dif) {
if (!dif) dif--;
/* error: a < b */ t1 = *(ap++);
return 0; t2 = (t1 - borrow) & BN_MASK2;
while (dif) { *(rp++) = t2;
dif--; borrow &= (t1 == 0);
t1 = *(ap++);
t2 = (t1 - 1) & BN_MASK2;
*(rp++) = t2;
if (t1)
break;
}
} }
if (dif && ap != rp)
memcpy(rp, ap, sizeof(*rp) * dif);
r->top = max; r->top = max;
r->neg = 0; r->neg = 0;
bn_correct_top(r); bn_correct_top(r);
return (1); return 1;
} }
int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b) int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
{ {
int max; int max;
int add = 0, neg = 0; int add = 0, neg = 0;
const BIGNUM *tmp;
bn_check_top(a); bn_check_top(a);
bn_check_top(b); bn_check_top(b);
@ -199,6 +163,8 @@ int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
*/ */
if (a->neg) { if (a->neg) {
if (b->neg) { if (b->neg) {
const BIGNUM *tmp;
tmp = a; tmp = a;
a = b; a = b;
b = tmp; b = tmp;
@ -215,25 +181,25 @@ int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
if (add) { if (add) {
if (!BN_uadd(r, a, b)) if (!BN_uadd(r, a, b))
return (0); return 0;
r->neg = neg; r->neg = neg;
return (1); return 1;
} }
/* We are actually doing a - b :-) */ /* We are actually doing a - b :-) */
max = (a->top > b->top) ? a->top : b->top; max = (a->top > b->top) ? a->top : b->top;
if (bn_wexpand(r, max) == NULL) if (bn_wexpand(r, max) == NULL)
return (0); return 0;
if (BN_ucmp(a, b) < 0) { if (BN_ucmp(a, b) < 0) {
if (!BN_usub(r, b, a)) if (!BN_usub(r, b, a))
return (0); return 0;
r->neg = 1; r->neg = 1;
} else { } else {
if (!BN_usub(r, a, b)) if (!BN_usub(r, a, b))
return (0); return 0;
r->neg = 0; r->neg = 0;
} }
bn_check_top(r); bn_check_top(r);
return (1); return 1;
} }