Author: Robert Hyatt
Date: 21:10:54 12/02/98
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On December 02, 1998 at 22:27:27, Bruce Moreland wrote: > >On December 02, 1998 at 14:30:59, Tom Kerrigan wrote: > >>You're right, if other people are running faster with chars, then the statement >>I made was wrong. >> >>I tested this with my own program, and moving from chars to ints for a few >>critical arrays sped up the program by more than 5%. Maybe I'm the exception to >>the rule. > >Could be, that's data too. Another argument for trying it. > >I think it is possible that either could be better in specific situations. > >The chars are smaller which may have some influence on cache behavior, and the >ints are bite-sized as far as the processor is concerned, so it doesn't have to >mess around with clearing the top-most bits. > >bruce There's two other explanations too. (1) changing the size of the board caused something *else* to become better aligned on a cache boundary. IE the famous case where you can delete an unused variable declaration and your program slows down or speeds up. (2) the famous direct-mapped L2 cache problem where even the same program can vary in NPS significantly due to the real memory pages it occupies not mapping into the L2 cache very efficiently sometimes... Both are a pain.
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