/* 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;

 	}