Article View: comp.std.c
Article #2483Re: pointers for speed
From: Dave P. Schaumann
Date: Mon, 25 Feb 1991 23:36
Date: Mon, 25 Feb 1991 23:36
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1404 bytes
In article <1998@gold.gvg.tek.com> shaunc@gold.gvg.tek.com (Shaun Case) writes: >I know that when you repeatedly access something like > >foo.a.b.c.d[11].value > >it is better to declare a (register) pointer, assign it the address >of foo.a.b.c.d[11].value, and do manipulations on that, since it >is faster. Oh really? Seems to me that &foo.a.b.c.d[0] is a constant that can be computed *at compile time*. That means that (unless your comiler is totally brain-dead) accessing foo.a.b.c.d[0] should be as fast as accessing a normal element of an array of the same type. Yes, calculating the address does take a bit longer, but that calculation is done once by the compiler, and is known forever more. Now, if you had foo->a->b->c->d, you would certainly want to keep the address of d in a variable, rather than indirecting 4 times. -- Dave Schaumann | Is this question undecidable? dave@cs.arizona.edu |
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!usc!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!ncar!noao!arizona!dave From: dave@cs.arizona.edu (Dave P. Schaumann) Newsgroups: comp.std.c Subject: Re: pointers for speed Message-ID: <955@caslon.cs.arizona.edu> Date: 25 Feb 91 23:36:24 GMT References: <1998@gold.gvg.tek.com> Organization: U of Arizona CS Dept, Tucson Lines: 23