Author: Miguel A. Ballicora
Date: 11:34:32 07/14/01
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On July 14, 2001 at 14:23:15, Miguel A. Ballicora wrote: >On July 14, 2001 at 02:16:17, Bruce Moreland wrote: > >>On July 14, 2001 at 01:59:31, TEERAPONG TOVIRAT wrote: >> >>>Hi, >>> >>>I've been trying to reduce my hashtable size,so that I can gain >>>more entries. At first,I try to pack three structure tag into one >>>integer it looks like this... >>> >>> new integer = (flag<<a)|(depth<<b)|(value) >>> >>>It fails because value is signed int the rest are unsigned. >>>Could anyone solve the problem? >>> >>>Thanks in advance, >>>Teerapong >> >>Use a 16-bit integer for the value and two chars for the other stuff. That gets >>you into 32-bits without screwing anything up. Be forewarned that 16-bit >>integers are evil, so don't use the things repeatedly in inner loop. "Ooh, >>these things are smaller, so the processor must like them better, so I'll make >>all my ints into shorts whenever possible", is the utterance of someone who is >>going to spend a confused afternoon wondering why they got 25% slower. >> >>Also, if you are going to use these things, put the two chars together so your >>struct is char-char-word or word-char-char, but never char-word-char, which will >>either cause the structure to pad (I believe to 48 bits in this case) or will >>cause problems due to bad alignment if you get the structure to pack. > >This is clean and bug-free way to do it; however, since the padding or the >absence of it is not guaranteed, I will add that the size of the hashtable entry >should be checked with (sizeof HASH_STRUCTURE == WhateverWeExpect) and allocate >the number of entries according to the result of sizeof rather than a #define >value. Otherwise, it could break in some compiler. >To force the padding I think that it could be done with a structure that It should be read "to force NO PADDING"... Regards, Miguel
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