Is there an existing gem or script that converts numbers to comp-3/packed decimal format?

Question

Continuing with my adventure to convert COBOL to a Ruby program, I have to convert a decimal digit to a comp-3/packed decimal format. Anyone know of a simple Ruby script or gem that does this? Berns

Hi Mark-Andre. Do you know where I might find the algorithm, or at least an explanation of the algorithm that would help me understand how to spend those five minutes? I understand nipples (or nybbles) are involved, and a byte can have exactly 2, which means all of my digits should end up looking great! :) — btelles, Apr 12 '10 at 19:55
I looked at http://www.3480-3590-data-conversion.com/article-packed-fields.html and answered with some code. Good luck. — Marc-André Lafortune, Apr 12 '10 at 20:21
Actually, there's even builtin nibble packing in Ruby. Who knew. Answer updated. — Marc-André Lafortune, Apr 12 '10 at 20:57

Marc-André Lafortune · Accepted Answer · 2010-04-12T21:52:50.007

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Ruby knows how to pack nibbles, so it turns out to be quite easy:

def pack_comp(n)
  s = n.abs.to_s + (n < 0 ? "d" : "c")
  s = "0" + s if s.size.odd?
  [s].pack("H*")
end

edited Apr 12 '10 at 21:52

answered Apr 12 '10 at 20:20

Marc-André Lafortune

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No problem. And no, you're not. BTW, it did take me more than 5 minutes :-) And my first solution was overkill too. – Marc-André Lafortune Apr 12 '10 at 21:21
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Idiots are only geniuses who don't realise it yet. – Ryan Bigg Apr 12 '10 at 21:34
to_s produces "nibbles" (4 bit values)? I'm not a Ruby expert, but they look like just string characters (8 or 16 bit values) to me. – Ira Baxter Apr 07 '11 at 08:48
@Ira: Indeed, `to_s` does not produce nibbles, it just converts to a string (i.e. does the decimal expansion). It is `pack("H*")` that "converts" these characters to nibbles. HTH – Marc-André Lafortune Apr 07 '11 at 11:52

Is there an existing gem or script that converts numbers to comp-3/packed decimal format?

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