/* crypto/bn/bn_mod.c */

/* Includes code written by Lenka Fibikova <fibikova@exp-math.uni-essen.de>

 * for the OpenSSL project. */

/* ====================================================================

 * Copyright (c) 1998-2000 The OpenSSL Project.  All rights reserved.

 *

 * 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 above 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 acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"

 *

 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to

 *    endorse or promote products derived from this software without

 *    prior written permission. For written permission, please contact

 *    openssl-core@openssl.org.

 *

 * 5. Products derived from this software may not be called "OpenSSL"

 *    nor may "OpenSSL" appear in their names without prior written

 *    permission of the OpenSSL Project.

 *

 * 6. Redistributions of any form whatsoever must retain the following

 *    acknowledgment:

 *    "This product includes software developed by the OpenSSL Project

 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"

 *

 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY

 * EXPRESSED 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 OpenSSL PROJECT OR

 * ITS 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.

 * ====================================================================

 *

 * This product includes cryptographic software written by Eric Young

 * (eay@cryptsoft.com).  This product includes software written by Tim

 * Hudson (tjh@cryptsoft.com).

 *

 */

/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)

 * All rights reserved.

 *

 * This package is an SSL implementation written

 * by Eric Young (eay@cryptsoft.com).

 * 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 (tjh@cryptsoft.com).

 * 

 * 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 (eay@cryptsoft.com)"

 *    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 (tjh@cryptsoft.com)"

 * 

 * 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 "cryptlib.h"

#include "bn_lcl.h"

#if 0 /* now just a #define */

EXPORT_C int BN_mod(BIGNUM *rem, const BIGNUM *m, const BIGNUM *d, BN_CTX *ctx)

	{

	return(BN_div(NULL,rem,m,d,ctx));

	/* note that  rem->neg == m->neg  (unless the remainder is zero) */

	}

#endif

EXPORT_C int BN_nnmod(BIGNUM *r, const BIGNUM *m, const BIGNUM *d, BN_CTX *ctx)

	{

	/* like BN_mod, but returns non-negative remainder

	 * (i.e.,  0 <= r < |d|  always holds) */

	if (!(BN_mod(r,m,d,ctx)))

		return 0;

	if (!r->neg)

		return 1;

	/* now   -|d| < r < 0,  so we have to set  r := r + |d| */

	return (d->neg ? BN_sub : BN_add)(r, r, d);

}

EXPORT_C int BN_mod_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m, BN_CTX *ctx)

	{

	if (!BN_add(r, a, b)) return 0;

	return BN_nnmod(r, r, m, ctx);

	}

/* BN_mod_add variant that may be used if both  a  and  b  are non-negative

 * and less than  m */

EXPORT_C int BN_mod_add_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m)

	{

	if (!BN_uadd(r, a, b)) return 0;

	if (BN_ucmp(r, m) >= 0)

		return BN_usub(r, r, m);

	return 1;

	}

EXPORT_C int BN_mod_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m, BN_CTX *ctx)

	{

	if (!BN_sub(r, a, b)) return 0;

	return BN_nnmod(r, r, m, ctx);

	}

/* BN_mod_sub variant that may be used if both  a  and  b  are non-negative

 * and less than  m */

EXPORT_C int BN_mod_sub_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m)

	{

	if (!BN_sub(r, a, b)) return 0;

	if (r->neg)

		return BN_add(r, r, m);

	return 1;

	}

/* slow but works */

EXPORT_C int BN_mod_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,

	BN_CTX *ctx)

	{

	BIGNUM *t;

	int ret=0;

	bn_check_top(a);

	bn_check_top(b);

	bn_check_top(m);

	BN_CTX_start(ctx);

	if ((t = BN_CTX_get(ctx)) == NULL) goto err;

	if (a == b)

		{ if (!BN_sqr(t,a,ctx)) goto err; }

	else

		{ if (!BN_mul(t,a,b,ctx)) goto err; }

	if (!BN_nnmod(r,t,m,ctx)) goto err;

	bn_check_top(r);

	ret=1;

err:

	BN_CTX_end(ctx);

	return(ret);

	}

EXPORT_C int BN_mod_sqr(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)

	{

	if (!BN_sqr(r, a, ctx)) return 0;

	/* r->neg == 0,  thus we don't need BN_nnmod */

	return BN_mod(r, r, m, ctx);

	}

EXPORT_C int BN_mod_lshift1(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)

	{

	if (!BN_lshift1(r, a)) return 0;

	bn_check_top(r);

	return BN_nnmod(r, r, m, ctx);

	}

/* BN_mod_lshift1 variant that may be used if  a  is non-negative

 * and less than  m */

EXPORT_C int BN_mod_lshift1_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *m)

	{

	if (!BN_lshift1(r, a)) return 0;

	bn_check_top(r);

	if (BN_cmp(r, m) >= 0)

		return BN_sub(r, r, m);

	return 1;

	}

EXPORT_C int BN_mod_lshift(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m, BN_CTX *ctx)

	{

	BIGNUM *abs_m = NULL;

	int ret;

	if (!BN_nnmod(r, a, m, ctx)) return 0;

	if (m->neg)

		{

		abs_m = BN_dup(m);

		if (abs_m == NULL) return 0;

		abs_m->neg = 0;

		}

	ret = BN_mod_lshift_quick(r, r, n, (abs_m ? abs_m : m));

	bn_check_top(r);

	if (abs_m)

		BN_free(abs_m);

	return ret;

	}

/* BN_mod_lshift variant that may be used if  a  is non-negative

 * and less than  m */

EXPORT_C int BN_mod_lshift_quick(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m)

	{

	if (r != a)

		{

		if (BN_copy(r, a) == NULL) return 0;

		}

	while (n > 0)

		{

		int max_shift;

		/* 0 < r < m */

		max_shift = BN_num_bits(m) - BN_num_bits(r);

		/* max_shift >= 0 */

		if (max_shift < 0)

			{

			BNerr(BN_F_BN_MOD_LSHIFT_QUICK, BN_R_INPUT_NOT_REDUCED);

			return 0;

			}

		if (max_shift > n)

			max_shift = n;

		if (max_shift)

			{

			if (!BN_lshift(r, r, max_shift)) return 0;

			n -= max_shift;

			}

		else

			{

			if (!BN_lshift1(r, r)) return 0;

			--n;

			}

		/* BN_num_bits(r) <= BN_num_bits(m) */

		if (BN_cmp(r, m) >= 0) 

			{

			if (!BN_sub(r, r, m)) return 0;

			}

		}

	bn_check_top(r);

	return 1;

	}