/* 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);

 	}