Well the basic idea is this: suppose we have an array like 
1 2 3 4 5 6 a b c

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initially, x points to 1, y points to a: 
x           y
1 2 3 4 5 6 a b c

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We want to move a b c all the way to the left,so we swap numbers and letters: 
      x           y
a b c 4 5 6 1 2 3

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Now the rightmost elements are scrambled. Note that y at this stage points to the element one off the right end of the array. We restore its position: 
$y = $offset_y if $y == @$ary;

      x     y
a b c 4 5 6 1 2 3

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Now we basically have a smaller array 4 5 6 1 2 3 and we want to swap 4 5 6 and 1 2 3. Hence, recursion. But it's a tail call, aka 'while loop in disguise', so: 
sub do_swaps {
    my ( $ary, $offset_x, $offset_y, $swaps ) = @_;
    my ( $x, $y ) = ( $offset_x, $offset_y );

    while ( $offset_y != @$ary ) {
        for ( $offset_x .. ( $offset_y - 1 ) ) {
            $y         = $offset_y if $y == @$ary;
            my $temp   = $ary->[$x];
            $ary->[$x] = $ary->[$y];
            $ary->[$y] = $temp;
            $x += 1;
            $y += 1;

            $swaps += 1;
        }
    ( $offset_x, $offset_y ) = ( $x, $y );
    }
    
    return $swaps;
}

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Same thing... I think :)

In reply to Re^3: [OT] Swapping buffers in place. by Anonymous Monk
in thread [OT] Swapping buffers in place. by BrowserUk

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