ByteModTableInit.C

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// Copyright (C) 2001, Compaq Computer Corporation
// 
// This file is part of Vesta.
// 
// Vesta is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// 
// Vesta is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
// 
// You should have received a copy of the GNU Lesser General Public
// License along with Vesta; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

// Last modified on Thu Aug  1 14:30:24 EDT 2002 by kcschalk@shr.intel.com
//      modified on Tue Jun 25 19:15:08 EDT 2002 by ken@xorian.net

#include "ByteModTable.H"

// Define the storage for ByteModTable
Poly ByteModTable[8][256];

// Initialization of ByteModTable constants------------------------------------

// Force ByteModTable to be initialized early with a static instance
// of a special initializer class.
class ByteModTableInit
{
public:
  typedef Poly table_type[8][256];
  ByteModTableInit(table_type &table) throw ();
};

static ByteModTableInit byte_mod_table_init(ByteModTable);

static void TimesX(Poly& p) throw ()
  /* Set "p" to the polynomial "p" times "X" mod "POLY_IRRED". */
{
  short x127flag = (p.w[0] & POLY_X63_W);
  p.w[0] >>= 1;
  if (p.w[1] & POLY_X63_W) p.w[0] |= POLY_ONE_W;
  p.w[1] >>= 1;
  if (x127flag) PolyInc(p, POLY_IRRED);
}

// This is the fucntion which actually computes ByteModTable.
ByteModTableInit::ByteModTableInit(table_type &table) throw ()
{
  Poly PowerTable[256], p;

  // TimesX above assumes this, as does FP::Send and FP::Recv, as well
  // as other code in this package.
  assert(PolyVal::WordCnt == 2);

  // Compute "PowerTable"
  int i;
  p = POLY_ONE;
  for(i = 0; i < 256; TimesX(p),i++)
    {
      PowerTable[i] = p;
    }

  // Compute ByteModTable
  int j, k;
  const unsigned char X7 = 1;
  for(i = 0; i < 8; i++)
    {
      for(j = 0; j < 256; j++)
        {
          p = POLY_ZERO;
          for(k=0; k < 8; k++)
            {
              if(j & (X7 << k))
                {
                  PolyInc(p, PowerTable[191-(i*8)-k]);
                }
            }

          // ByteModTable[i][j] = p;
          table[i][j] = p;
        }
    }
}

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