bn_add.c

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/* crypto/bn/bn_add.c */
/* Copyright (C) 1995-1998 Eric Young ([email protected])
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young ([email protected]).
 * 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 ([email protected]).
 * 
 * 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 ([email protected])"
 *    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 ([email protected])"
 * 
 * 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"

/* r can == a or b */
int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
    {
    const BIGNUM *tmp;
    int a_neg = a->neg, ret;

    bn_check_top(a);
    bn_check_top(b);

    /*  a +  b  a+b
     *  a + -b  a-b
     * -a +  b  b-a
     * -a + -b  -(a+b)
     */
    if (a_neg ^ b->neg)
        {
        /* only one is negative */
        if (a_neg)
            { tmp=a; a=b; b=tmp; }

        /* we are now a - b */

        if (BN_ucmp(a,b) < 0)
            {
            if (!BN_usub(r,b,a)) return(0);
            r->neg=1;
            }
        else
            {
            if (!BN_usub(r,a,b)) return(0);
            r->neg=0;
            }
        return(1);
        }

    ret = BN_uadd(r,a,b);
    r->neg = a_neg;
    bn_check_top(r);
    return ret;
    }

/* unsigned add of b to a */
int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
    {
    int max,min,dif;
    BN_ULONG *ap,*bp,*rp,carry,t1,t2;
    const BIGNUM *tmp;

    bn_check_top(a);
    bn_check_top(b);

    if (a->top < b->top)
        { tmp=a; a=b; b=tmp; }
    max = a->top;
    min = b->top;
    dif = max - min;

    if (bn_wexpand(r,max+1) == NULL)
        return 0;

    r->top=max;


    ap=a->d;
    bp=b->d;
    rp=r->d;

    carry=bn_add_words(rp,ap,bp,min);
    rp+=min;
    ap+=min;
    bp+=min;

    if (carry)
        {
        while (dif)
            {
            dif--;
            t1 = *(ap++);
            t2 = (t1+1) & BN_MASK2;
            *(rp++) = t2;
            if (t2)
                {
                carry=0;
                break;
                }
            }
        if (carry)
            {
            /* carry != 0 => dif == 0 */
            *rp = 1;
            r->top++;
            }
        }
    if (dif && rp != ap)
        while (dif--)
            /* copy remaining words if ap != rp */
            *(rp++) = *(ap++);
    r->neg = 0;
    bn_check_top(r);
    return 1;
    }

/* unsigned subtraction of b from a, a must be larger than b. */
int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
    {
    int max,min,dif;
    register BN_ULONG t1,t2,*ap,*bp,*rp;
    int i,carry;
#if defined(IRIX_CC_BUG) && !defined(LINT)
    int dummy;
#endif

    bn_check_top(a);
    bn_check_top(b);

    max = a->top;
    min = b->top;
    dif = max - min;

    if (dif < 0)    /* hmm... should not be happening */
        {
        BNerr(BN_F_BN_USUB,BN_R_ARG2_LT_ARG3);
        return(0);
        }

    if (bn_wexpand(r,max) == NULL) return(0);

    ap=a->d;
    bp=b->d;
    rp=r->d;

#if 1
    carry=0;
    for (i = min; i != 0; i--)
        {
        t1= *(ap++);
        t2= *(bp++);
        if (carry)
            {
            carry=(t1 <= t2);
            t1=(t1-t2-1)&BN_MASK2;
            }
        else
            {
            carry=(t1 < t2);
            t1=(t1-t2)&BN_MASK2;
            }
#if defined(IRIX_CC_BUG) && !defined(LINT)
        dummy=t1;
#endif
        *(rp++)=t1&BN_MASK2;
        }
#else
    carry=bn_sub_words(rp,ap,bp,min);
    ap+=min;
    bp+=min;
    rp+=min;
#endif
    if (carry) /* subtracted */
        {
        if (!dif)
            /* error: a < b */
            return 0;
        while (dif)
            {
            dif--;
            t1 = *(ap++);
            t2 = (t1-1)&BN_MASK2;
            *(rp++) = t2;
            if (t1)
                break;
            }
        }
#if 0
    memcpy(rp,ap,sizeof(*rp)*(max-i));
#else
    if (rp != ap)
        {
        for (;;)
            {
            if (!dif--) break;
            rp[0]=ap[0];
            if (!dif--) break;
            rp[1]=ap[1];
            if (!dif--) break;
            rp[2]=ap[2];
            if (!dif--) break;
            rp[3]=ap[3];
            rp+=4;
            ap+=4;
            }
        }
#endif

    r->top=max;
    r->neg=0;
    bn_correct_top(r);
    return(1);
    }

int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
    {
    int max;
    int add=0,neg=0;
    const BIGNUM *tmp;

    bn_check_top(a);
    bn_check_top(b);

    /*  a -  b  a-b
     *  a - -b  a+b
     * -a -  b  -(a+b)
     * -a - -b  b-a
     */
    if (a->neg)
        {
        if (b->neg)
            { tmp=a; a=b; b=tmp; }
        else
            { add=1; neg=1; }
        }
    else
        {
        if (b->neg) { add=1; neg=0; }
        }

    if (add)
        {
        if (!BN_uadd(r,a,b)) return(0);
        r->neg=neg;
        return(1);
        }

    /* We are actually doing a - b :-) */

    max=(a->top > b->top)?a->top:b->top;
    if (bn_wexpand(r,max) == NULL) return(0);
    if (BN_ucmp(a,b) < 0)
        {
        if (!BN_usub(r,b,a)) return(0);
        r->neg=1;
        }
    else
        {
        if (!BN_usub(r,a,b)) return(0);
        r->neg=0;
        }
    bn_check_top(r);
    return(1);
    }