Parity2D_4x4.h

Go to the documentation of this file.

/* -*- mode:C++ -*- */

/*
  Parity2D_4x4.h Support for simple 2D parity management
  Copyright (C) 2014 The Regents of the University of New Mexico.  All rights reserved.

  This library 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.

  This library 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 General Public License
  along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
  USA
*/

#ifndef PARITY2D_4x4_H
#define PARITY2D_4x4_H

#include "itype.h"

namespace MFM {

  class Parity2D_4x4
  {
  public:
    enum {
      W = 4,
      H = 4,
      DATA_BITS = W * H,
      ECC_BITS = W + H + 1,
      TABLE_SIZE = 1 << DATA_BITS,
      INDEX_MASK = TABLE_SIZE - 1,
      ECC_MASK = (1 << ECC_BITS) - 1
    };

    static u32 Compute2DParity(u32 dataBits) {
      return eccTable[dataBits&INDEX_MASK];
    }

    static u32 ComputeParitySlow(u32 dataBits);

    static u32 Add2DParity(u32 dataBits) {
      return (dataBits&INDEX_MASK) | (Compute2DParity(dataBits) << DATA_BITS);
    }

    static bool Remove2DParity(u32 allBits, u32 & dataBits) {
      u32 corrected = CheckAndCorrect2DParity(allBits);
      if (corrected == 0)
        return false;
      dataBits = corrected&INDEX_MASK;
      return true;
    }

    static bool Check2DParity(const u32 allBits) {
      u32 eccBits = (allBits>>DATA_BITS) & ECC_MASK;
      u32 dataBits = allBits&INDEX_MASK;
      return Compute2DParity(dataBits) == eccBits;
    }

    static u32 CheckAndCorrect2DParity(const u32 allBits) {
      u32 eccBits = (allBits>>DATA_BITS) & ECC_MASK;
      u32 dataBits = allBits&INDEX_MASK;
      if (Compute2DParity(dataBits) == eccBits)
        return allBits;
      return Correct2DParityIfPossible(allBits);
    }

    static u32 Correct2DParityIfPossible(u32 allBits);

    static const u8 indices2D[H + 1][W + 1];

  private:
    static const u16 eccTable[TABLE_SIZE];
    static const u32 masks[H + 1 + W + 1];
  };
} /* namespace MFM */

#endif /*PARITY2D_4x4_H*/