snakeindex.h

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#ifndef SNAKEINDEX_H
#define SNAKEINDEX_H

#include <typedefs.h>

template< typename T = int >
class snakeindex
{
  T dcurrent;
  T current;
public:

  T const rows;
  T const columns;
  T const length;

  snakeindex
  (
    T const _columns, 
    T const _length, 
    bool forward=true
  );

  void reset();
  boolc operator !() const 
    { return (current>=0)&&(current<length); }
  void operator ++ ()
    { current += dcurrent; }
  void pos(T & row, T & col) const;
  void pos(T & k2) const;

};

//---------------------------------------------------------
// Implementation


template< typename T >
void snakeindex<T>::pos(T & k2) const
{
  T row;
  T col;
  pos(row,col);
  k2 = row*columns+col;
}

template< typename T >
void snakeindex<T>::pos(T & row, T & col) const
{
  row = (current - (current % columns))/columns;
  col = current-row*columns;
  if ((row % 2)==1)
    col = columns-1-col;
}

template< typename T >
void snakeindex<T>::reset()
{
  if (dcurrent>0)
    current=0;
  else
    current=length-1;
}


template< typename T >
snakeindex<T>::snakeindex
(
  T const _columns, 
  T const _length,
  boolc forward
)
  : rows(_length % _columns), columns(_columns), length(_length)
{
  if (forward)
    dcurrent=1;
  else
    dcurrent=-1;

}


#endif