/* 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 */

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

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);

}

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

 */

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;

}

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

 */

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 */

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);

}

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);

}

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

 */

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;

}

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

 */

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;

}