You can factor more work out of the inner loop, but I would expect the win to be very minor: 
my $bxScaled = $bx * 16;
my $byScaled = $by * 16;

for my $x (0 .. 15) {
    my $xScaled = 16 * $x;

    # These calculations were factored out of the inner loop
    my $rx = $bxScaled + $x;
    my $tiles_for_rx = $tiles[$rx];

    for my $y (0 .. 15) {
        # this calculates the tile index we are currently at,
        # using the x and y coords in this block
        my $tile_index = $y + $xScaled;

        # this calculates the real y value of this tile
        my $ry = $byScaled + $y;

        # insert type data into the internal map array and
        # note that there was change in this block if applicable
        my $tile = $tiles_for_rx->[$ry][$bz][type];
        if (!defined $tile || $$tile != $type_data[$tile_index])
        {
            $changed = 1;
            $$tile = $type_data[$tile_index];
        }
    }
}

[download]
Incidentally I'm puzzled at the array access of type. Should that be a $type? Or perhaps a hash access? Either way the current version looks like a bug.

Incidentally another cause of your win over the original is that you're using lexical variables consistently, which I believe are slightly faster than package variables.

In reply to Re^2: How to speed up a nested loop? by tilly
in thread How to speed up a nested loop? by Xenofur

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