Author: Dan Newman
Date: 13:16:24 04/18/00
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On April 18, 2000 at 14:27:52, Andrew Dados wrote: >On April 18, 2000 at 12:48:28, Tom Kerrigan wrote: > >>On April 18, 2000 at 12:45:36, John Coffey wrote: >> >>>I am writting a data structure that I have to copy with every new node. I was >>>planning on using 16 bytes, but could maybe get it down to 8 using short >>>integers. I am wondering if short integers (16 bits) can be accessed any faster >>>than 32 bit integers or if they are actually slower. Also will the difference >> >>They're actually slower. >> > >I'll be picky: that depends on alignment - may be faster or slower or same...:) >Technically mov ax,[data16] has same timing as mov eax,[data32]. > >>>between copying 8 bytes and 16 bytes per node make any difference in >>>terms of my overall speed? >> >>I doubt it. That's just 2 extra instructions, moving data around in cache. >> >>-Tom I've found that doing 16-bit stuff tends to be a lot slower than both 32-bit and 8-bit and 8-bit stuff to be only a little slower than 32-bit. (This on P6's, Celerons, and PIII's.) Sometimes 8-bit stuff can be faster than 32-bit. If you have a large array of integral type that's frequently accessed, and all you need is 8-bits per entry, you might get a speed improvement going to byte sized entries: the processor can grab a larger number of enrtries in a cache line which may more than offset the higher cost of 8-bit ops. -Dan.
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