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From: | "Alexei A. Frounze" <alex DOT fru AT mtu-net DOT ru> |
Newsgroups: | comp.os.msdos.djgpp |
Subject: | Re: inefficiency of GCC output code & -O problem |
Date: | Thu, 13 Apr 2000 22:10:59 +0400 |
Organization: | MTU-Intel ISP |
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To: | djgpp AT delorie DOT com |
DJ-Gateway: | from newsgroup comp.os.msdos.djgpp |
Reply-To: | djgpp AT delorie DOT com |
Dieter Buerssner wrote: > It would be interesting to know, what the performance difference > of this code and the code without the inline assembly was. Well, I don't think it's possible to write extremely fast 3d renderer w/o ASM at all (at least on i386+ CPUs). Don't you think Wolf3d, Doom, Descent and Quake would not be as fast as they are, if they were written in pure C (even Watcom C, which was one of the best compilers then)? > But, why use this? Gcc will most probably produce exactly the > same code by > > du >>= SUB_BITS; > dv >>= SUB_BITS; It will load EAX, shift EAX and put the result back instead of plane shift using a memory reference. At least I saw this in disassembly. thanks. Alexei A. Frounze ----------------------------------------- Homepage: http://alexfru.chat.ru Mirror: http://members.xoom.com/alexfru
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