BIGNUM_xor.cc

/*
 * Copyright 2003 Michael A. Marsh, Cornell University. All rights reserved.
 * This software is released under the modified BSD license.
 * See the file LICENSE in the top-level directory for details.
 */
//
// $Id: BIGNUM_xor.cc,v 1.3 2004/05/19 15:56:46 mmarsh Exp $
//
// $Log: BIGNUM_xor.cc,v $
// Revision 1.3  2004/05/19 15:56:46  mmarsh
// *** empty log message ***
//
// Revision 1.2  2003/11/04 22:31:47  mmarsh
// *** empty log message ***
//
//

#include "BIGNUM_xor.h"
#include "CODEX_Exceptions/BignumExceptions.h"

using namespace CODEX_Ciphers;

BIGNUM *
CODEX_Ciphers::BIGNUM_xor( BIGNUM * r , const BIGNUM * a , const BIGNUM * b )
{
   if ( 0 == a )
   {
      throw CODEX_Exceptions::BignumNullException( __FILE__ , __LINE__ );
   }
   if ( 0 == b )
   {
      throw CODEX_Exceptions::BignumNullException( __FILE__ , __LINE__ );
   }

   BIGNUM * retVal = 0;
   if ( 0 != r )
   {
      retVal = r;
   }
   else
   {
      retVal = BN_new();
      if ( 0 == retVal )
      {
         throw CODEX_Exceptions::BignumNullException( __FILE__ , __LINE__ );
      }
   }
   BN_clear( retVal );

   const BIGNUM *at, *bt;
  
   if ( a->top < b->top )
   {
      at = b;
      bt = a;
   }
   else
   {
      at = a;
      bt = b;
   }
  
   bn_expand2( retVal, at->top );
  
   int i;
   for ( i = 0 ; i < bt->top ; i++ )
   {
      retVal->d[i] = at->d[i] ^ bt->d[i];
   }
   for ( ; i < at->top ; i++ )
   {
      retVal->d[i] = at->d[i];
   }
   
   retVal->top = at->top;
   bn_fix_top(retVal);
   return retVal;
}

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