bn_word.c

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/* crypto/bn/bn_word.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"

BN_ULONG BN_mod_word(const BIGNUM *a, BN_ULONG w)
    {
#ifndef BN_LLONG
    BN_ULONG ret=0;
#else
    BN_ULLONG ret=0;
#endif
    int i;

    if (w == 0)
        return (BN_ULONG)-1;

    bn_check_top(a);
    w&=BN_MASK2;
    for (i=a->top-1; i>=0; i--)
        {
#ifndef BN_LLONG
        ret=((ret<<BN_BITS4)|((a->d[i]>>BN_BITS4)&BN_MASK2l))%w;
        ret=((ret<<BN_BITS4)|(a->d[i]&BN_MASK2l))%w;
#else
        ret=(BN_ULLONG)(((ret<<(BN_ULLONG)BN_BITS2)|a->d[i])%
            (BN_ULLONG)w);
#endif
        }
    return((BN_ULONG)ret);
    }

BN_ULONG BN_div_word(BIGNUM *a, BN_ULONG w)
    {
    BN_ULONG ret = 0;
    int i, j;

    bn_check_top(a);
    w &= BN_MASK2;

    if (!w)
        /* actually this an error (division by zero) */
        return (BN_ULONG)-1;
    if (a->top == 0)
        return 0;

    /* normalize input (so bn_div_words doesn't complain) */
    j = BN_BITS2 - BN_num_bits_word(w);
    w <<= j;
    if (!BN_lshift(a, a, j))
        return (BN_ULONG)-1;

    for (i=a->top-1; i>=0; i--)
        {
        BN_ULONG l,d;
        
        l=a->d[i];
        d=bn_div_words(ret,l,w);
        ret=(l-((d*w)&BN_MASK2))&BN_MASK2;
        a->d[i]=d;
        }
    if ((a->top > 0) && (a->d[a->top-1] == 0))
        a->top--;
    ret >>= j;
    bn_check_top(a);
    return(ret);
    }

int BN_add_word(BIGNUM *a, BN_ULONG w)
    {
    BN_ULONG l;
    int i;

    bn_check_top(a);
    w &= BN_MASK2;

    /* degenerate case: w is zero */
    if (!w) return 1;
    /* degenerate case: a is zero */
    if(BN_is_zero(a)) return BN_set_word(a, w);
    /* handle 'a' when negative */
    if (a->neg)
        {
        a->neg=0;
        i=BN_sub_word(a,w);
        if (!BN_is_zero(a))
            a->neg=!(a->neg);
        return(i);
        }
    /* Only expand (and risk failing) if it's possibly necessary */
    if (((BN_ULONG)(a->d[a->top - 1] + 1) == 0) &&
            (bn_wexpand(a,a->top+1) == NULL))
        return(0);
    i=0;
    for (;;)
        {
        if (i >= a->top)
            l=w;
        else
            l=(a->d[i]+w)&BN_MASK2;
        a->d[i]=l;
        if (w > l)
            w=1;
        else
            break;
        i++;
        }
    if (i >= a->top)
        a->top++;
    bn_check_top(a);
    return(1);
    }

int BN_sub_word(BIGNUM *a, BN_ULONG w)
    {
    int i;

    bn_check_top(a);
    w &= BN_MASK2;

    /* degenerate case: w is zero */
    if (!w) return 1;
    /* degenerate case: a is zero */
    if(BN_is_zero(a))
        {
        i = BN_set_word(a,w);
        if (i != 0)
            BN_set_negative(a, 1);
        return i;
        }
    /* handle 'a' when negative */
    if (a->neg)
        {
        a->neg=0;
        i=BN_add_word(a,w);
        a->neg=1;
        return(i);
        }

    if ((a->top == 1) && (a->d[0] < w))
        {
        a->d[0]=w-a->d[0];
        a->neg=1;
        return(1);
        }
    i=0;
    for (;;)
        {
        if (a->d[i] >= w)
            {
            a->d[i]-=w;
            break;
            }
        else
            {
            a->d[i]=(a->d[i]-w)&BN_MASK2;
            i++;
            w=1;
            }
        }
    if ((a->d[i] == 0) && (i == (a->top-1)))
        a->top--;
    bn_check_top(a);
    return(1);
    }

int BN_mul_word(BIGNUM *a, BN_ULONG w)
    {
    BN_ULONG ll;

    bn_check_top(a);
    w&=BN_MASK2;
    if (a->top)
        {
        if (w == 0)
            BN_zero(a);
        else
            {
            ll=bn_mul_words(a->d,a->d,a->top,w);
            if (ll)
                {
                if (bn_wexpand(a,a->top+1) == NULL) return(0);
                a->d[a->top++]=ll;
                }
            }
        }
    bn_check_top(a);
    return(1);
    }