my $VALUE = $MyMatrix[$a][$b];

##</code><code>##

my $VALUE = (vec($MyMatrix, ($a & 7), 8) >> $b) & 1;

##</code><code>##

#!/usr/bin/perl -w

use strict;
use warnings;

my $i;
my $j;

# Create our test matrix
my $MyMatrix = NewMatrix();

# Shows that all matrix values are initially ZERO.
DisplayMatrix();

# Set all matrix values to ONE.
for ($i = 0; $i < 5; $i++)
{
  for ($j = 0; $j < 5; $j++)
  {
    $MyMatrix = SetMatrixValue($MyMatrix, $i, $j, 1);
  }
}

DisplayMatrix();

# Clear somes random values...
$MyMatrix = SetMatrixValue($MyMatrix, 1, 4, 0);
$MyMatrix = SetMatrixValue($MyMatrix, 2, 0, 0);
$MyMatrix = SetMatrixValue($MyMatrix, 2, 3, 0);
DisplayMatrix();

# Flip bits from zero to one and one to zero.
$MyMatrix = NOT_Matrix($MyMatrix);
DisplayMatrix();

exit;

#
# This function reads a bit from the 5x5 matrix.
# Returns either 1 or 0.
# Usage: GetMatrixValue(MATRIX_STRING, X_POS, Y_POS)
#
sub GetMatrixValue
{
  my $MATRIX    = GetMatrixStr(shift);
  my $X         = (shift) & 7;
  my $Y         = (shift) & 7;

  # Make sure the pointers are within the right range.
  $X <= 4 or $X = 4;
  $Y <= 4 or $Y = 4;

  return (vec($MATRIX, $Y, 8) >> $X) & 1;
}


#
# This function changes a bit in the 5x5 matrix string.
# Returns the new matrix string.
# Usage: NEW_MATRIX_STRING = SetMatrixValue(MATRIX_STRING, X_POS, Y_POS, NEW_VALUE)
#
sub SetMatrixValue
{
  my $MATRIX    = GetMatrixStr(shift);
  my $X         = (shift) & 7;
  my $Y         = (shift) & 7;
  my $NEW_VALUE = (shift) & 1;

  # Make sure the pointers are within the right range.
  $X <= 4 or $X = 4;
  $Y <= 4 or $Y = 4;

  vec($MATRIX, ($Y << 3) + $X, 1) = $NEW_VALUE;
  return $MATRIX;
}

#
# This function makes sure that the matrix
# string is exactly 5 bytes long.
# Usage: MATRIX_STRING = GetMatrixStr(MATRIX_STRING)
#
sub GetMatrixStr
{
  my $Z = "\0" x 5;
  @_ or return $Z;
  defined $_[0] or return $Z;
  return (length($_[0]) == 5) ? $_[0] : substr("$_[0]$Z", 0, 5);
}

#
# This function performs bitwise NOT operation on all the
# bits of the matrix and returns the matrix string.
#  Usage: MATRIX_STRING = NOT_Matrix(MATRIX_STRING)
#
sub NOT_Matrix
{
  my $MATRIX = GetMatrixStr(shift);
  for (my $i = 0; $i < 5; $i++)
  {
    vec($MATRIX, $i, 8) = ~vec($MATRIX, $i, 8);
  }
  return $MATRIX;
}

sub NewMatrix { return "\0" x 5; }

sub DisplayMatrix
{
  my $j;
  print "\n\n--- MATRIX " . ('-' x 60) . "\n\n";
  for (my $i = 0; $i < 5; $i++)
  {
    for ($j = 0; $j < 5; $j++)
    {
      print "\t[$i,$j]=" . GetMatrixValue($MyMatrix, $i, $j);
    }
    print "\n";
  }
  PAUSE();
}

sub PAUSE
{
  $| = 1;
  print "\nPRESS ENTER TO CONTINUE...\n";
  <STDIN>;
  return 0;
}