/* crypto/bn/bn_recp.c */

/* 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 <stdio.h>

#include "cryptlib.h"

#include "bn_lcl.h"

EXPORT_C void BN_RECP_CTX_init(BN_RECP_CTX *recp)

	{

	BN_init(&(recp->N));

	BN_init(&(recp->Nr));

	recp->num_bits=0;

	recp->flags=0;

	}

EXPORT_C BN_RECP_CTX *BN_RECP_CTX_new(void)

	{

	BN_RECP_CTX *ret;

	if ((ret=(BN_RECP_CTX *)OPENSSL_malloc(sizeof(BN_RECP_CTX))) == NULL)

		return(NULL);

	BN_RECP_CTX_init(ret);

	ret->flags=BN_FLG_MALLOCED;

	return(ret);

	}

EXPORT_C void BN_RECP_CTX_free(BN_RECP_CTX *recp)

	{

	if(recp == NULL)

	    return;

	BN_free(&(recp->N));

	BN_free(&(recp->Nr));

	if (recp->flags & BN_FLG_MALLOCED)

		OPENSSL_free(recp);

	}

EXPORT_C int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *d, BN_CTX *ctx)

	{

	if (!BN_copy(&(recp->N),d)) return 0;

	BN_zero(&(recp->Nr));

	recp->num_bits=BN_num_bits(d);

	recp->shift=0;

	return(1);

	}

EXPORT_C int BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *x, const BIGNUM *y,

	BN_RECP_CTX *recp, BN_CTX *ctx)

	{

	int ret=0;

	BIGNUM *a;

	const BIGNUM *ca;

	BN_CTX_start(ctx);

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

	if (y != NULL)

		{

		if (x == y)

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

		else

			{ if (!BN_mul(a,x,y,ctx)) goto err; }

		ca = a;

		}

	else

		ca=x; /* Just do the mod */

	ret = BN_div_recp(NULL,r,ca,recp,ctx);

err:

	BN_CTX_end(ctx);

	bn_check_top(r);

	return(ret);

	}

EXPORT_C int BN_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m,

	BN_RECP_CTX *recp, BN_CTX *ctx)

	{

	int i,j,ret=0;

	BIGNUM *a,*b,*d,*r;

	BN_CTX_start(ctx);

	a=BN_CTX_get(ctx);

	b=BN_CTX_get(ctx);

	if (dv != NULL)

		d=dv;

	else

		d=BN_CTX_get(ctx);

	if (rem != NULL)

		r=rem;

	else

		r=BN_CTX_get(ctx);

	if (a == NULL || b == NULL || d == NULL || r == NULL) goto err;

	if (BN_ucmp(m,&(recp->N)) < 0)

		{

		BN_zero(d);

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

		BN_CTX_end(ctx);

		return(1);

		}

	/* We want the remainder

	 * Given input of ABCDEF / ab

	 * we need multiply ABCDEF by 3 digests of the reciprocal of ab

	 *

	 */

	/* i := max(BN_num_bits(m), 2*BN_num_bits(N)) */

	i=BN_num_bits(m);

	j=recp->num_bits<<1;

	if (j>i) i=j;

	/* Nr := round(2^i / N) */

	if (i != recp->shift)

		recp->shift=BN_reciprocal(&(recp->Nr),&(recp->N),

			i,ctx); /* BN_reciprocal returns i, or -1 for an error */

	if (recp->shift == -1) goto err;

	/* d := |round(round(m / 2^BN_num_bits(N)) * recp->Nr / 2^(i - BN_num_bits(N)))|

	 *    = |round(round(m / 2^BN_num_bits(N)) * round(2^i / N) / 2^(i - BN_num_bits(N)))|

	 *   <= |(m / 2^BN_num_bits(N)) * (2^i / N) * (2^BN_num_bits(N) / 2^i)|

	 *    = |m/N|

	 */

	if (!BN_rshift(a,m,recp->num_bits)) goto err;

	if (!BN_mul(b,a,&(recp->Nr),ctx)) goto err;

	if (!BN_rshift(d,b,i-recp->num_bits)) goto err;

	d->neg=0;

	if (!BN_mul(b,&(recp->N),d,ctx)) goto err;

	if (!BN_usub(r,m,b)) goto err;

	r->neg=0;

#if 1

	j=0;

	while (BN_ucmp(r,&(recp->N)) >= 0)

		{

		if (j++ > 2)

			{

			BNerr(BN_F_BN_DIV_RECP,BN_R_BAD_RECIPROCAL);

			goto err;

			}

		if (!BN_usub(r,r,&(recp->N))) goto err;

		if (!BN_add_word(d,1)) goto err;

		}

#endif

	r->neg=BN_is_zero(r)?0:m->neg;

	d->neg=m->neg^recp->N.neg;

	ret=1;

err:

	BN_CTX_end(ctx);

	bn_check_top(dv);

	bn_check_top(rem);

	return(ret);

	} 

/* len is the expected size of the result

 * We actually calculate with an extra word of precision, so

 * we can do faster division if the remainder is not required.

 */

/* r := 2^len / m */

EXPORT_C int BN_reciprocal(BIGNUM *r, const BIGNUM *m, int len, BN_CTX *ctx)

	{

	int ret= -1;

	BIGNUM *t;

	BN_CTX_start(ctx);

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

	if (!BN_set_bit(t,len)) goto err;

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

	ret=len;

err:

	bn_check_top(r);

	BN_CTX_end(ctx);

	return(ret);

	}