bn_sqr.c

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/* crypto/bn/bn_sqr.c */
/* Copyright (C) 1995-1998 Eric Young ([e-mail])
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young ([e-mail]).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson ([e-mail]).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young ([e-mail])"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson ([e-mail])"
 * 
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <stdio.h>
#include "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, BIGNUM * a, BN_CTX * ctx)
{
    int max, al;
    int ret = 0;
    BIGNUM *tmp, *rr;

#ifdef BN_COUNT
    printf("BN_sqr %d * %d\n", a->top, a->top);
#endif
    bn_check_top(a);

    al = a->top;
    if (al <= 0) {
	r->top = 0;
	return (1);
    }

    BN_CTX_start(ctx);
    rr = (a != r) ? r : BN_CTX_get(ctx);
    tmp = BN_CTX_get(ctx);
    if (tmp == NULL)
	goto err;

    max = (al + al);
    if (bn_wexpand(rr, max + 1) == NULL)
	goto err;

    r->neg = 0;
    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(a, k * 2) == NULL)
		    goto err;
		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->top = max;
    if ((max > 0) && (rr->d[max - 1] == 0))
	rr->top--;
    if (rr != r)
	BN_copy(r, rr);
    ret = 1;
  err:
    BN_CTX_end(ctx);
    return (ret);
}

/* tmp must have 2*n words */
void bn_sqr_normal(BN_ULONG * r, BN_ULONG * a, int n, BN_ULONG * tmp)
{
    int i, j, max;
    BN_ULONG *ap, *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, BN_ULONG * a, int n2, BN_ULONG * t)
{
    int n = n2 / 2;
    int zero, c1;
    BN_ULONG ln, lo, *p;

#ifdef BN_COUNT
    printf(" bn_sqr_recursive %d * %d\n", n2, n2);
#endif
    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, n2 * sizeof(BN_ULONG));
    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