Messages in this thread | | | Date | Sat, 10 Apr 1999 08:51:27 +0200 | From | Janos Farkas <> | Subject | Re: more on hash functions |
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On 1999-04-09 at 19:06:03, Chuck Lever wrote: > thanks for the information. the missing piece, though, is how expensive > is a multiplication operation relative to a couple of memory references? > that's the direct trade-off when tuning these hash tables.
[About '030 again]
Sorry, missed it; its two cycles for every additional memory access, in most circumstances. This is the difference even between an instruction operating in registers and the same doing it from/to memory, and this is how longer an instruction takes if it has more instruction words. It's true even for 32-bit accesses on the right system (ie. 32-bit memory bus -- common).
[Just to shortly recap: a multiplication is taking 28/44 cycles at worst, (16/32 bit), and highly depends on the bit patterns; very roughly about how much 1 bit is set in the multiplier (not true, just to get the picture)]
Janos
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