Message-Id:	<199811131631.QAA10528@remus.clara.net>
From:	"Arthur" <arfa AT clara DOT net>
To:	<djgpp AT delorie DOT com>
Subject:	RE: fixed point + allegro
Date:	Fri, 13 Nov 1998 16:30:48 -0000
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Reply-To:	djgpp AT delorie DOT com

> Hi everybody,
>
>     I need some help... i'd like to convert those fixed point routines of
> allegro to use in a C++ Compiler 16 bits. But almost all code of
> fixed point
> in allegro is in assembler.

You won't be able to convert it to 16-bit directly, as Allegro uses 32-bit
fixed-point numbers (16.16).

> Does anybody have source code of
> anyother fixed
> point functions (add, minus, mul, sub) ? I'm tring to convert allegro
> functions but i really don't understand the AT&T format yet....

Just out of interest, why are you trying to convert it to another compiler?

Fixed point is really simple. To do your own 32-bit fixed point code:

short i; // 16-bit integer
long  f, f1, f2; // 32-bit fixed (stored in long - Allegro typedefs it)

convert int to fixed: f = i << 16;
convert fixed to int: i = f >> 16;
add two fixed numbers: f1 += f2;
sub two fixed numbers: f1 -= f2;
mul two fixed numbers: f1 *= (f2 >> 16);
div two fixed numbers: f1 /= (f2 >> 16);

Allegro also checks for overflow errors on these functions, but as you can
see,  fixed point math is pretty easy to do. If you want this for a 16-bit
compiler, change all the "16" above to "8".

HTH

James Arthur
jaa AT arfa DOT clara DOT net
ICQ#15054819

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