Author: Eric Oldre
Date: 15:13:02 06/20/04
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On June 20, 2004 at 17:29:28, Mathieu Pagé wrote: >Hi Eric, > >I don't know anything about fruit, but I think (from experience) that size will >_always_ of the form: > > size = 2^X > >This allow to have a fast KeyToIndex function that will use a binary operation >and no division. Let's takle your own example, but instead of size = 33 let's >take size = 32 that is 2^6 > >you have size = 32 (or 100000b) > >so your mask is 32 - 1 = 31 (or 11111b) > >so when you do: > > key & mask > >you always get something >= 0 and < 32 > >So the key is to have a size that is a power of 2. > >You could also use any value for the size and take the remainder of the division >as a index, but you will have to problem in this case: > >1) for some size you will get a non-uniform distribution of you entries >2) a division is slower than a binary AND (That is in fact a modulo 2) > >hope it help. > >Mathieu P. Mathieu, thanks for your great explaination. it makes perfect sense now. I knew that i must be missing something, in this case, that size always is 2^x.
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