From:	Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: twin complement ......
Date:	18 Aug 2000 11:20:38 GMT
Organization:	Aachen University of Technology (RWTH)
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Florent <florent AT oih DOT rwth-aachen DOT de> wrote:
> Is there any fonctions for the twin complement ?

You cause quite some confusion, here, by using the wrong term. The
thing you're talking about is usually called 'two's-complement'.  It's
the way negative numbers are represented in integers, on almost all
existing types of computers.

The problem you're having is that you assume the machine can *guess*
what type of data element you want to convert: a byte, a 16bit word,
or a 32bit one. Two's-complement is only defined with respect to a
fixed size of datatype. You can't calculcate it with 0x10 stored in an
'int' variable, and expect to get the value of a single-byte
two's-complement.

Actually, due to the way C evaluated integer expressions, you'll
always operate in int, or longer datatypes. So you'll have to mask to
your required 'target' datatype later.
-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.

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