Then maybe something like this. It should still be ~25 faster than the original for the general case: 
    sub interleave {

        my $str    = shift;
        my $filler = 64; # Char number.

        my $hi_bytes = pack 'v*', unpack 'C*', $str;
        my $lo_bytes = pack 'n*', ($filler) x length $str;

        return $hi_bytes | $lo_bytes;
    }

[download]

--
John.

In reply to Re^3: Interleaving bytes in a string quickly by jmcnamara
in thread Interleaving bytes in a string quickly by BrowserUk

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