From: Ken Bloom <kbloom@...>
Date: 2008-01-11T10:10:03+09:00
Subject: Re: Question about Hex => Signed Int

On Thu, 10 Jan 2008 13:19:46 -0500, Joel VanderWerf wrote:
> Tim Conner wrote:
>> Thanks for that.  Is there a ruby function which I can pass a hex
>> number and it works out if it is +/- and then returns the correct
>> decimal value?
> 
> Convert to unsigned first, like above, then do something like this:
> 
>      length = 32 # in bits; you have to choose this
> 
>      mid = 2**(length-1)
>      max_unsigned = 2**length
>      to_signed = proc {|n| (n>=mid) ? n - max_unsigned : n}
> 
>      p to_signed["0xFF467A7B".to_i(16)]
>      p to_signed["0x38CFEF".to_i(16)]
> 
> See http://en.wikipedia.org/wiki/Twos_complement.

Why go through all the trouble to make this a proc?

--Ken

-- 
Ken (Chanoch) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/