in reply to Interleaving bytes in a string quickly


For the specific example of interleaving a null byte this should be ~50 times faster than the original solution: 
    $out = pack 'v*', unpack 'C*', $buf;

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--
John.

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Re^2: Interleaving bytes in a string quickly
by BrowserUk (Patriarch) on Feb 26, 2010 at 14:46 UTC

    Yes, that was an unfortunate choice of example. In the real thing, it isn't a null byte. Nice lateral thinking though!

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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[reply]

      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.

[reply]
[d/l]
        this variation... 
        $s = time;
$out4 = (pack 'v*', unpack 'C*', $buf) | ("\x00$filler" x length $buf)
+;
print time() - $s, "\n";

        [download]
        ... introduces very low overhead.
[reply]
[d/l]

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