SortingNetwork.cpp

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// MIT License
//
// Copyright (c) 2023 Ian Parberry
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// IN THE SOFTWARE.
 
#include "SortingNetwork.h"
 
 
CSortingNetwork::CSortingNetwork(): CComparatorNetwork(){
  m_pGrayCode = new CBinaryGrayCode;
} //constructor
 
 
CSortingNetwork::~CSortingNetwork(){
  delete m_pGrayCode;
} //destructor
 
 
void CSortingNetwork::InitValues(const size_t first, const size_t last){
  for(size_t i=first; i<=last; i++) //for each level in range
    for(size_t j=0; j<m_nWidth; j++) //for each channel
      m_nValue[i][j] = 0; //set the value on this channel at that level to zero
} //InitValues
 
 
void CSortingNetwork::Initialize(){ 
  m_pGrayCode->Initialize(); //initialize the Gray code to all zeros.
  InitValues(0, m_nDepth - 1); //initialize the network values to all zeros.
  m_nZeros = m_nWidth - 1; //all zeros
} //initialize
 
 
size_t CSortingNetwork::FlipInput(size_t j, const size_t first, const size_t last){
  const size_t nBit = m_nValue[first][j] ^ 1;
  m_nZeros += nBit? -1: 1; //if nBit has flipped to 1, one less zero, else one more
  
  for(size_t i=first; i<=last; i++){ //for each layer in range
    m_nValue[i][j] = nBit; //flip the value on channel j at that level 
 
    const size_t k = m_nComparator[i][j]; //channel joined via a comparator
 
    if(xor(m_nValue[i][k], j > k))
      j = k;
  } //for
 
  return j;
} //FlipInput
 
 
bool CSortingNetwork::StillSorts(const size_t delta){
  const size_t nTarget = m_nValue[0][delta]? m_nZeros: m_nZeros - 1;
  return FlipInput(delta, 0, m_nDepth - 1) == nTarget;
} //StillSorts
 
 
bool CSortingNetwork::Sorts(){ 
  size_t i = 0; //index of bit to flip
  bool bSorts = true; //assume it sorts until we find otherwise
  Initialize(); //intialize input and values in comparator network to zero
 
  while(bSorts && i < m_nWidth){ //bail if it doesn't sort, or we've tried all binary inputs
    i = m_pGrayCode->Next(); //next bit to flip in Gray code order
    bSorts = bSorts && (i >= m_nWidth || StillSorts(i)); //check whether it still sorts when this bit is flipped
  } //while
 
  return bSorts;
} //Sorts