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bn_word.c

/* crypto/bn/bn_word.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"

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);
      }


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