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C:/temp/src/j2k/QNX4/PositionTracker.hpp

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class PositionTracker
{
public:

    PostionTracker();
    virtual PositionTracker();

    int Wrap( int val, int max ) {
        if ( val < 0   ) return (val + max + 1);
        if ( val > max ) return (val - max - 1);
        return val;
    }

    int Check( int bit, int val ) {
        if ( bit < 0  ||  bit > 65536 ) return -1;
        int bit2 = 1 << bit;
        return ( ( val && bit2 ) == bit2 );

      // int bit2 = 2 ^ bit;
      // return ( ( val && bit2 ) == bit2 );
    }

    int UpdateTrack() {
      
        int r = board->Read();
        int i = 0;
        int t = 0;
        int Tracks[ 16 ];
        int OldTracks[ 16 ];

        for( int k = 1; k < 65536; k *= 2 ) { // 16
            t = ( ( r & k) == k );
            OldTracks[ i ] = Tracks[ i ];
            Tracks[ i ] = t;
            i++;
        }

        for( int m = 0; m < 3; m++ ) {  // 3
            int pos    = Train[ m ]->position;
            int prev   = Train[ m ]->prev_position;
            int prevT1 = Wrap( tr - 1, 15 );
            int nextT1 = Wrap( tr + 1, 15 );
            int prevT3 = Wrap( tr - 3, 15 );
            int nextT3 = Wrap( tr + 3, 15 );

            Train[ m ]->prev_position = pos;

            if ( Tracks[ pos ] ) {  // Still there
                Tracks[ pos ] = m;
            } else if ( OldTracks[ nextT1 ] == m ) { // Train was After
                    Tracks[ pos ] = m;
            } else if ( OldTracks[ prevT1 ] == m ) { // Train was Before
                    Tracks[ pos ] = m;
            } else if ( OldTracks[ nextT3 ] == m ) { // Train was After by 3
                    Tracks[ pos ] = m;
            } else if ( OldTracks[ prevT3 ] == m ) { // Train was Before by 3
                    Tracks[ pos ] = m;
            } 
        }
    }
};

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