my @table2, @table3;
foreach my $i (0..256) { 
  $table2[$i]= $i >> 6;
  $table3[$i]= $i << 2 & 63;
}

...
my $number[0]= $byte[0] & 63;
my $number[1]= $table2[$byte[0]] + $table3[$byte[1]];
...