From: Mark Hubbart <discord@...>
Date: 2004-09-23T05:26:58+09:00
Subject: Re: negative numbers and binary formats


On Sep 22, 2004, at 11:14 AM, Paul wrote:

> Im trying to take a negative integer value, convert it to its binary
> equivalent, and save its hex value
>
> -7 -> 1111 1001 -> F9
>
>
>  I was hoping to use sprintf, but:
>
> irb(main):017:0> b = sprintf("%4b" , a)
> => "..1001"
> irb(main):018:0>
>
> The .. that appear break any further processing. So my questions are:
>
> Why the dots, and what are they?
>
> How do I do what Im trying to do - given my -7 in the example may be a
> 1 byte, 2 byte or 4 byte value. ( Im sure its some magic with
> pack....)

well, if all you need is the hex part, here you go:

class Integer
   def internal_hex
     # choose a packing strategy
     case self
     when (-128..127) # char
       [self].pack('c').unpack('C').first.to_s 16
     when (-32768..32767) # short
       [self].pack('s').unpack('S').first.to_s 16
     when (-2147483648..2147483647) # long
       [self].pack('l').unpack('L').first.to_s 16
     else
       "too big!" #  :)
     end
   end
end

-7.internal_hex   #=>"f9"


the hex string will be in big-endian (network) byte-order; that's the 
way to_s(16) does it.

cheers
Mark


>
> Thanks
>
> Paul
>