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Date: Wed, 02 Nov 2005 16:49:14 +0200
Subject: Re: Simulation of fixed point in c WITH DIFFERENT BIT-WIDTH
Newsgroups: comp.lang.ada
References: <1130690498.388857.225170@g49g2000cwa.googlegroups.com>
 <dka62u$8pl$1@hudsucker.umdac.umu.se>
From: "Martin Krischik" <krischik@users.sourceforge.net>
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Date: 2005-11-02T16:49:14+02:00
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Am 02.11.2005, 12:57 Uhr, schrieb Colin Paul Gloster  
<Colin_Paul_Gloster@ACM.org>:

> Mnamky posted to news:comp.lang.ada :
>
> "Hi all;
>
> Consider the following exaple
> y = x * b'
>
> where x is 12-bit wordlength and 11-bit fraction
> and b is 16-bit wordlength and 14-bit fraction
>
> simulation of this code is rather easy im Matlab but how could we do a
> full analysis of this code in C with a good precision?"
>
> I fail to see the relevance of this to Ada. In C, you could use ints and
> interpret some bits as an integer and some bits as a vulgar fraction, as
> in computer games books for 386s and 486s (before Pentiums which had
> faster floating point support than integer support) in the 1990s, such
> as "Building a 3D Engine in C++" and La Mothe; Ratcliff; et al.,
> "Tricks of the Game Programming Gurus", SAMS Publishing.
>
> A worse way would be to use bitfields.

Well sounds to me you want a fixed poind type:

http://en.wikibooks.org/wiki/Ada_Programming/Types/delta

Tricky part is all the bit fideling you wish for. In Ada you usualy ask  
for a needed precision and prehaps a overall bit size and then let Ada  
sort out the rest.

Martin