From: SerDevian <scriven AT CS DOT ColoState DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Allegro fixed math routines
Date: Tue, 04 Feb 1997 14:20:43 -0700
Organization: XYZZ Software Co.
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Message-ID: <32F7A82B.446B@CS.ColoState.edu>
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To: djgpp AT delorie DOT com
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Christian Tamasiu wrote:
> Why doesnt, for example, " x = y + 24 " (both x and y fixed) work???
> However, " x = y + itofix(24) " worked. But even more strange using some
> other values, it worked without itofix. It is also sometimes need using
> *,/,- and sometimes not.
> Why???

Do you know what fixed-point numbers actually are?

If not, x and y (fixed) are equal to their "integer" equivalents times
64k. So if x was 3, and y was 4, they are really 3*65536 and 4*65536.  

If you use "x=y+24;" you'll get x = (4*65536) + 24, which is not much
different than y originally was.  

When you use "x = y + itofix(24);" you're doing x = (4*65536) +
(24*65536).

Note that these "*65536" aren't really multiplied, but instead done by
shifting in binary (which is much faster).

The hex layout of a fixed-point number is this:
0xiiiiffff (where i is the integer part and f is the fractional part)
and the layout of a regular integer is like this:
0xiiiiiiii

Note that itofix(0x00001234) is the same as 0x12340000.


-- Yamaha / XYZZ          "May farce the with be you."
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