241 lines
6.0 KiB
C
241 lines
6.0 KiB
C
/*-
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* Copyright (c) 1990, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Margo Seltzer.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#if defined(LIBC_SCCS) && !defined(lint)
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static char sccsid[] = "@(#)hash_func.c 8.4 (Berkeley) 11/7/95";
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#endif /* LIBC_SCCS and not lint */
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#include <sys/types.h>
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#include <db.h>
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#include "hash.h"
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#include "page.h"
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#include "extern.h"
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extern u_int32_t db_hash1 __P((const void *, size_t));
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extern u_int32_t db_hash2 __P((const void *, size_t));
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extern u_int32_t db_hash3 __P((const void *, size_t));
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extern u_int32_t db_hash4 __P((const void *, size_t));
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extern u_int32_t db_hash5 __P((const void *, size_t));
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/* Default hash function. */
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/* Ariel: switched to hash5 (FNV hash).
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* hash4 distribution performance is poor on dictionary words and binary data
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*/
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u_int32_t (*__default_hash) __P((const void *, size_t)) = db_hash5;
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/*
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* Assume that we've already split the bucket to which this key hashes,
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* calculate that bucket, and check that in fact we did already split it.
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*
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* EJB's original hsearch hash.
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*/
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#define PRIME1 37
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#define PRIME2 1048583
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u_int32_t
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db_hash1(key, len)
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const void *key;
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size_t len;
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{
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u_int32_t h;
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u_int8_t *k;
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h = 0;
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k = (u_int8_t *)key;
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/* Convert string to integer */
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while (len--)
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h = h * PRIME1 ^ (*k++ - ' ');
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h %= PRIME2;
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return (h);
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}
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/*
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* Phong Vo's linear congruential hash
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*/
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#define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
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u_int32_t
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db_hash2(key, len)
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const void *key;
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size_t len;
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{
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u_int32_t h;
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u_int8_t *e, c, *k;
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k = (u_int8_t *)key;
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e = k + len;
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for (h = 0; k != e;) {
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c = *k++;
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if (!c && k > e)
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break;
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dcharhash(h, c);
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}
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return (h);
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}
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/*
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* This is INCREDIBLY ugly, but fast. We break the string up into 8 byte
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* units. On the first time through the loop we get the "leftover bytes"
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* (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle
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* all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If
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* this routine is heavily used enough, it's worth the ugly coding.
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*
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* Ozan Yigit's original sdbm hash.
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*/
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u_int32_t
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db_hash3(key, len)
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const void *key;
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size_t len;
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{
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u_int32_t n, loop;
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u_int8_t *k;
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#define HASHC n = *k++ + 65599 * n
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n = 0;
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k = (u_int8_t *)key;
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if (len > 0) {
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loop = (len + 8 - 1) >> 3;
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switch (len & (8 - 1)) {
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case 0:
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do { /* All fall throughs */
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HASHC;
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case 7:
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HASHC;
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case 6:
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HASHC;
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case 5:
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HASHC;
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case 4:
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HASHC;
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case 3:
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HASHC;
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case 2:
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HASHC;
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case 1:
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HASHC;
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} while (--loop);
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}
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}
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return (n);
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}
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/* Chris Torek's hash function. */
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u_int32_t
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db_hash4(key, len)
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const void *key;
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size_t len;
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{
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u_int32_t h, loop;
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u_int8_t *k;
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#define HASH4a h = (h << 5) - h + *k++;
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#define HASH4b h = (h << 5) + h + *k++;
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#define HASH4 HASH4b
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h = 0;
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k = (u_int8_t *)key;
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if (len > 0) {
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loop = (len + 8 - 1) >> 3;
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switch (len & (8 - 1)) {
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case 0:
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do { /* All fall throughs */
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HASH4;
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case 7:
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HASH4;
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case 6:
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HASH4;
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case 5:
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HASH4;
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case 4:
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HASH4;
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case 3:
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HASH4;
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case 2:
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HASH4;
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case 1:
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HASH4;
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} while (--loop);
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}
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}
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return (h);
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}
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/*
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* Fowler/Noll/Vo hash
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*
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* The magic is in the interesting relationship between the special
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* prime 16777619 (2^24 + 403) and 2^32 and 2^8. If you need a hash to
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* base 2^64 instead of 2^32, let me know and I'll search for a similar
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* magic prime.
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*
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* This hash was able to process 234936 words from the web2 dictionary
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* without any 32 bit collisions. It also hashes 4 byte integers
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* really well (no collisions for the range 1..10000000)
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*/
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u_int32_t
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db_hash5(const void * key, size_t len)
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{
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u_int32_t val; /* current hash value */
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uchar_t *k = (uchar_t *) key;
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uchar_t *key_end = k + len;
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/*
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* Fowler/Noll/Vo hash - hash each character in the string
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*
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* The basis of the hash algorithm was taken from an idea
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* sent by Email to the IEEE Posix P1003.2 mailing list from
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* Phong Vo (kpv@research.att.com) and Glenn Fowler
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* (gsf@research.att.com).
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* Landon Curt Noll (chongo@toad.com) later improved on their
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* algorithm to come up with Fowler/Noll/Vo hash.
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*
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*/
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for (val = 0; k < key_end; ++k) {
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val *= 16777619;
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val ^= *k;
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}
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/* our hash value, (was: mod the hash size) */
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return val;
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}
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