Path: chuka.playstation.co.uk!scea!greg_labrec@interactive.sony.com
From: "Wayne K. Werner" <wkwerner@con2.com>
Newsgroups: scea.yaroze.programming.3d_graphics
Subject: Re: A reply to one of Nick's questions.
Date: 3 Dec 1997 04:07:50 GMT
Organization: WermX Software
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I wrote:
 
That #define of ONE is *really* fixed point 4.12 (or 20.12 if you
are using longs).  Just wondering if Nick's algorithm (later in
this thread) works for this flavor of fixed point?

Then Joel emailed me:
 
If you are seeing "4.12" in the debugger when the decimal value is
4096,
it's because the debugger is displaying it improperly.  There is no
"standard" fixed point representation.  The Sony libraries use a 12
bit
fractional part in their fixed point representation.  4096=2^12 or
%1000000000000.  Thus, the fractional part is 0 and the decimal part
is 1. 
The debugger isn't set up right now to understand the Sony
fixed-point
format for the PlayStation.  Thus, I'm assuming this is where your
4.12 is
coming from.

Joel,

I didn't mean to imply that I was seeing the value, "4.12".  I meant
that
there is 4 binary digits of mantissa and 12 binary digits in the
fractional
part, 20 digits of mantissa for longs.  Indeed, the value of 4096
reps
the fixed point value of "1.000000000000", which is what I was trying
to
communicate.  That's what I get for knocking off messages late at
night
without thinking!

Wayne K. Werner
wkwerner@con2.com