From:	Paul Shirley <Paul AT foobar DOT co DOT uk DOT chocolat>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: graphics
Date:	Sun, 29 Dec 1996 18:31:20 +0000
Organization:	wot? me?
Lines:	27
Distribution:	world
Message-ID:	<kd3CcCA4jrxyEwsO@foobar.co.uk>
References:	<1 DOT 5 DOT 4 DOT 16 DOT 19961218230509 DOT 19f7ab66 AT mail DOT algonet DOT se>
	<32c3e184 DOT 1226804 AT news DOT eunet DOT fi> <01bbf50f$5ce75680$d42649c2 AT default>
Reply-To:	Paul Shirley <junk AT defeating DOT email DOT address>
NNTP-Posting-Host:	chocolat.foobar.co.uk
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

In article <01bbf50f$5ce75680$d42649c2 AT default>, Thomas Harte
<T DOT Harte AT btinternet DOT com> writes
>> Then draw pixels in this way:
>> #include<go32.h>
>> #include<sys/farptr.h>
>> _farpokeb(_dos_ds, 0xA0000+y*320+x, color);
>
>       Instead of multiplying by 320, I suggest you use two bit-shifts, 
>therefore
>changing the line to :-
>
>       _farpokeb(_dos_ds, 0xA0000 + (y << 8) + (y << 6) + x, colour);
>
>       . . . .as this is faster.
>
>               -Thomas

I suggest you leave it as *320, gcc will generate optimal code itself.
You will also be better able to read the source ;)

(It probably compiles faster as well... last time I looked the explicit
shift version got converted to the same code as a plain multiply. Its
probably a lot easier to detect a explicit multiply than the implied
one.)

---
Paul Shirley: shuffle chocolat before foobar for my real email address

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