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Article #11105Re: Relatively long cycle time in 486 LOOP instruction
From: Alan Rooks
Date: Wed, 16 Dec 1992 21:29
Date: Wed, 16 Dec 1992 21:29
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In article <fWFHrqe@quack.sac.ca.us> dfox@quack.sac.ca.us (David Fox) writes: > >I and others on a different network have had an ongoing thread about >386/486 assembler programming in general. One has posted recently >that the 486's LOOP and JMP [E]CX instructions seem to take an >inordinately long time, compared to other instructions that branch. > I've tested this on quite a few '486 motherboards, and always found the same result: all of the complex looping instructions (movs, lods, stos, scas, cmps, loop, loopz, loopnz, jecxz) take longer to execute than the series of operations that they are composed of. In other words, use simple instructions like dec, inc, mov, jnz, etc, and it will go faster. This is no doubt due to the '486's optimized execution of simple instructions. Remember: the '486 is a RISC, if you use the right instructions! :-) Alan Rooks University of Waterloo ajrooks@mansci1.uwaterloo.ca
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Newsgroups: comp.arch Path: arc1-ca.pugleaf.net!sparky!uunet!cs.utexas.edu!torn!watserv2.uwaterloo.ca!watserv1!mansci1.UWaterloo.ca!ajrooks From: ajrooks@mansci1.UWaterloo.ca (Alan Rooks) Subject: Re: Relatively long cycle time in 486 LOOP instruction Message-ID: <BzDFp3.KL4@watserv1.uwaterloo.ca> Keywords: 486 LOOP instruction cycle Sender: news@watserv1.uwaterloo.ca Organization: University of Waterloo References: <fWFHrqe@quack.sac.ca.us> Date: Wed, 16 Dec 1992 21:29:26 GMT Lines: 18