Hello Monks, I read the man pages for pack and unpack but must admit that I am a bit lost. Here is what I have: 
$data = '00010003206162';
$kategory = hex(substr($data,0,4));
$length   = hex(substr($data,4,4));
$contents = pack('H'.$length*2, substr($data, 8, length($data)));

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So the structure is:
- 4 characters with the kategory (hex number, here: 1),
- 4 characters with the length of the contents (hex number, here: 3),
- the contents as hex data (here: '206162' = ' ab')
- more data in the same or similar format

Now this code has to be really fast and I am sure it can be optimized. Since pack/unpack are very fast I hope that it is possible to do it along these lines (not working): 

my ($kat, $contents) = pack("h4 h4/H*", $data);

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It should somehow go with help of '/' I found in the pack manpage but must admit that I didn't understand it and have no idea how the given examples work.

As an additional complication sometimes the size isn't given directly but has to be subtracted from 65536, e.g. a value of 'fff5' means 65536 - 65525 = 11 as the size. But even if this esoteric counting can not be directly done it would help a lot if I could improve at least the more simple case above.

Any idea how this is best done?

Thanks
Michael

In reply to pack with count in the data by Anonymous Monk

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