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51 lines
1.7 KiB
51 lines
1.7 KiB
/**
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* \file
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*
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* \author Georg Hopp
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* \author Unknown (find out)
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*
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* \copyright
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* Copyright © 2014 Georg Hopp
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <ctype.h>
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#include <sys/types.h>
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/**
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* SDBM hashing algorithm:
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*
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* this algorithm was created for sdbm (a public-domain reimplementation of
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* ndbm) database library. it was found to do well in scrambling bits,
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* causing better distribution of the keys and fewer splits. it also happens
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* to be a good general hashing function with good distribution. the actual
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* function is hash(i) = hash(i - 1) * 65599 + str[i]; what is included below
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* is the faster version used in gawk. [there is even a faster, duff-device
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* version] the magic constant 65599 was picked out of thin air while
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* experimenting with different constants, and turns out to be a prime. this
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* is one of the algorithms used in berkeley db (see sleepycat) and elsewhere.
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*/
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unsigned long
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TR_sdbm(const unsigned char * str, size_t len)
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{
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unsigned long hash = 0;
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for(; 0 < len; str++, len--)
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hash = tolower(*str) + (hash << 6) + (hash << 16) - hash;
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return hash;
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}
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// vim: set ts=4 sw=4:
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