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/*
* Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (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_lcl.h"
/* r must not be a */
/*
* I've just gone over this and it is now %20 faster on x86 - eay - 27 Jun 96
*/
int BN_sqr(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
{
int max, al;
int ret = 0;
BIGNUM *tmp, *rr;
bn_check_top(a);
al = a->top;
if (al <= 0) {
r->top = 0;
r->neg = 0;
return 1;
}
BN_CTX_start(ctx);
rr = (a != r) ? r : BN_CTX_get(ctx);
tmp = BN_CTX_get(ctx);
if (!rr || !tmp)
goto err;
max = 2 * al; /* Non-zero (from above) */
if (bn_wexpand(rr, max) == NULL)
goto err;
if (al == 4) {
#ifndef BN_SQR_COMBA
BN_ULONG t[8];
bn_sqr_normal(rr->d, a->d, 4, t);
#else
bn_sqr_comba4(rr->d, a->d);
#endif
} else if (al == 8) {
#ifndef BN_SQR_COMBA
BN_ULONG t[16];
bn_sqr_normal(rr->d, a->d, 8, t);
#else
bn_sqr_comba8(rr->d, a->d);
#endif
} else {
#if defined(BN_RECURSION)
if (al < BN_SQR_RECURSIVE_SIZE_NORMAL) {
BN_ULONG t[BN_SQR_RECURSIVE_SIZE_NORMAL * 2];
bn_sqr_normal(rr->d, a->d, al, t);
} else {
int j, k;
j = BN_num_bits_word((BN_ULONG)al);
j = 1 << (j - 1);
k = j + j;
if (al == j) {
if (bn_wexpand(tmp, k * 2) == NULL)
goto err;
bn_sqr_recursive(rr->d, a->d, al, tmp->d);
} else {
if (bn_wexpand(tmp, max) == NULL)
goto err;
bn_sqr_normal(rr->d, a->d, al, tmp->d);
}
}
#else
if (bn_wexpand(tmp, max) == NULL)
goto err;
bn_sqr_normal(rr->d, a->d, al, tmp->d);
#endif
}
rr->neg = 0;
/*
* If the most-significant half of the top word of 'a' is zero, then the
* square of 'a' will max-1 words.
*/
if (a->d[al - 1] == (a->d[al - 1] & BN_MASK2l))
rr->top = max - 1;
else
rr->top = max;
if (r != rr && BN_copy(r, rr) == NULL)
goto err;
ret = 1;
err:
bn_check_top(rr);
bn_check_top(tmp);
BN_CTX_end(ctx);
return (ret);
}
/* tmp must have 2*n words */
void bn_sqr_normal(BN_ULONG *r, const BN_ULONG *a, int n, BN_ULONG *tmp)
{
int i, j, max;
const BN_ULONG *ap;
BN_ULONG *rp;
max = n * 2;
ap = a;
rp = r;
rp[0] = rp[max - 1] = 0;
rp++;
j = n;
if (--j > 0) {
ap++;
rp[j] = bn_mul_words(rp, ap, j, ap[-1]);
rp += 2;
}
for (i = n - 2; i > 0; i--) {
j--;
ap++;
rp[j] = bn_mul_add_words(rp, ap, j, ap[-1]);
rp += 2;
}
bn_add_words(r, r, r, max);
/* There will not be a carry */
bn_sqr_words(tmp, a, n);
bn_add_words(r, r, tmp, max);
}
#ifdef BN_RECURSION
/*-
* r is 2*n words in size,
* a and b are both n words in size. (There's not actually a 'b' here ...)
* n must be a power of 2.
* We multiply and return the result.
* t must be 2*n words in size
* We calculate
* a[0]*b[0]
* a[0]*b[0]+a[1]*b[1]+(a[0]-a[1])*(b[1]-b[0])
* a[1]*b[1]
*/
void bn_sqr_recursive(BN_ULONG *r, const BN_ULONG *a, int n2, BN_ULONG *t)
{
int n = n2 / 2;
int zero, c1;
BN_ULONG ln, lo, *p;
if (n2 == 4) {
# ifndef BN_SQR_COMBA
bn_sqr_normal(r, a, 4, t);
# else
bn_sqr_comba4(r, a);
# endif
return;
} else if (n2 == 8) {
# ifndef BN_SQR_COMBA
bn_sqr_normal(r, a, 8, t);
# else
bn_sqr_comba8(r, a);
# endif
return;
}
if (n2 < BN_SQR_RECURSIVE_SIZE_NORMAL) {
bn_sqr_normal(r, a, n2, t);
return;
}
/* r=(a[0]-a[1])*(a[1]-a[0]) */
c1 = bn_cmp_words(a, &(a[n]), n);
zero = 0;
if (c1 > 0)
bn_sub_words(t, a, &(a[n]), n);
else if (c1 < 0)
bn_sub_words(t, &(a[n]), a, n);
else
zero = 1;
/* The result will always be negative unless it is zero */
p = &(t[n2 * 2]);
if (!zero)
bn_sqr_recursive(&(t[n2]), t, n, p);
else
memset(&t[n2], 0, sizeof(*t) * n2);
bn_sqr_recursive(r, a, n, p);
bn_sqr_recursive(&(r[n2]), &(a[n]), n, p);
/*-
* t[32] holds (a[0]-a[1])*(a[1]-a[0]), it is negative or zero
* r[10] holds (a[0]*b[0])
* r[32] holds (b[1]*b[1])
*/
c1 = (int)(bn_add_words(t, r, &(r[n2]), n2));
/* t[32] is negative */
c1 -= (int)(bn_sub_words(&(t[n2]), t, &(t[n2]), n2));
/*-
* t[32] holds (a[0]-a[1])*(a[1]-a[0])+(a[0]*a[0])+(a[1]*a[1])
* r[10] holds (a[0]*a[0])
* r[32] holds (a[1]*a[1])
* c1 holds the carry bits
*/
c1 += (int)(bn_add_words(&(r[n]), &(r[n]), &(t[n2]), n2));
if (c1) {
p = &(r[n + n2]);
lo = *p;
ln = (lo + c1) & BN_MASK2;
*p = ln;
/*
* The overflow will stop before we over write words we should not
* overwrite
*/
if (ln < (BN_ULONG)c1) {
do {
p++;
lo = *p;
ln = (lo + 1) & BN_MASK2;
*p = ln;
} while (ln == 0);
}
}
}
#endif
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