hash_func.c revision 111010
11573Srgrimes/*- 21573Srgrimes * Copyright (c) 1990, 1993 31573Srgrimes * The Regents of the University of California. All rights reserved. 41573Srgrimes * 51573Srgrimes * This code is derived from software contributed to Berkeley by 61573Srgrimes * Margo Seltzer. 71573Srgrimes * 81573Srgrimes * Redistribution and use in source and binary forms, with or without 91573Srgrimes * modification, are permitted provided that the following conditions 101573Srgrimes * are met: 111573Srgrimes * 1. Redistributions of source code must retain the above copyright 121573Srgrimes * notice, this list of conditions and the following disclaimer. 131573Srgrimes * 2. Redistributions in binary form must reproduce the above copyright 141573Srgrimes * notice, this list of conditions and the following disclaimer in the 151573Srgrimes * documentation and/or other materials provided with the distribution. 161573Srgrimes * 3. All advertising materials mentioning features or use of this software 171573Srgrimes * must display the following acknowledgement: 181573Srgrimes * This product includes software developed by the University of 191573Srgrimes * California, Berkeley and its contributors. 201573Srgrimes * 4. Neither the name of the University nor the names of its contributors 211573Srgrimes * may be used to endorse or promote products derived from this software 221573Srgrimes * without specific prior written permission. 231573Srgrimes * 241573Srgrimes * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 251573Srgrimes * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 261573Srgrimes * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 271573Srgrimes * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 281573Srgrimes * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 291573Srgrimes * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 301573Srgrimes * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 311573Srgrimes * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 321573Srgrimes * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 331573Srgrimes * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 341573Srgrimes * SUCH DAMAGE. 351573Srgrimes */ 361573Srgrimes 371573Srgrimes#if defined(LIBC_SCCS) && !defined(lint) 381573Srgrimesstatic char sccsid[] = "@(#)hash_func.c 8.2 (Berkeley) 2/21/94"; 391573Srgrimes#endif /* LIBC_SCCS and not lint */ 4092889Sobrien#include <sys/cdefs.h> 4192889Sobrien__FBSDID("$FreeBSD: head/lib/libc/db/hash/hash_func.c 111010 2003-02-16 17:29:11Z nectar $"); 421573Srgrimes 431573Srgrimes#include <sys/types.h> 441573Srgrimes 451573Srgrimes#include <db.h> 461573Srgrimes#include "hash.h" 471573Srgrimes#include "page.h" 481573Srgrimes#include "extern.h" 491573Srgrimes 50111010Snectarstatic u_int32_t hash1(const void *, size_t) __unused; 51111010Snectarstatic u_int32_t hash2(const void *, size_t) __unused; 52111010Snectarstatic u_int32_t hash3(const void *, size_t) __unused; 5392905Sobrienstatic u_int32_t hash4(const void *, size_t); 541573Srgrimes 551573Srgrimes/* Global default hash function */ 5692941Sobrienu_int32_t (*__default_hash)(const void *, size_t) = hash4; 571573Srgrimes 581573Srgrimes/* 591573Srgrimes * HASH FUNCTIONS 601573Srgrimes * 611573Srgrimes * Assume that we've already split the bucket to which this key hashes, 621573Srgrimes * calculate that bucket, and check that in fact we did already split it. 631573Srgrimes * 641573Srgrimes * This came from ejb's hsearch. 651573Srgrimes */ 661573Srgrimes 671573Srgrimes#define PRIME1 37 681573Srgrimes#define PRIME2 1048583 691573Srgrimes 701573Srgrimesstatic u_int32_t 711573Srgrimeshash1(keyarg, len) 721573Srgrimes const void *keyarg; 7392889Sobrien size_t len; 741573Srgrimes{ 7592889Sobrien const u_char *key; 7692889Sobrien u_int32_t h; 771573Srgrimes 781573Srgrimes /* Convert string to integer */ 791573Srgrimes for (key = keyarg, h = 0; len--;) 801573Srgrimes h = h * PRIME1 ^ (*key++ - ' '); 811573Srgrimes h %= PRIME2; 821573Srgrimes return (h); 831573Srgrimes} 841573Srgrimes 851573Srgrimes/* 861573Srgrimes * Phong's linear congruential hash 871573Srgrimes */ 881573Srgrimes#define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c)) 891573Srgrimes 901573Srgrimesstatic u_int32_t 911573Srgrimeshash2(keyarg, len) 921573Srgrimes const void *keyarg; 931573Srgrimes size_t len; 941573Srgrimes{ 9592889Sobrien const u_char *e, *key; 9692889Sobrien u_int32_t h; 9792889Sobrien u_char c; 981573Srgrimes 991573Srgrimes key = keyarg; 1001573Srgrimes e = key + len; 1011573Srgrimes for (h = 0; key != e;) { 1021573Srgrimes c = *key++; 1031573Srgrimes if (!c && key > e) 1041573Srgrimes break; 1051573Srgrimes dcharhash(h, c); 1061573Srgrimes } 1071573Srgrimes return (h); 1081573Srgrimes} 1091573Srgrimes 1101573Srgrimes/* 1111573Srgrimes * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte 1121573Srgrimes * units. On the first time through the loop we get the "leftover bytes" 1131573Srgrimes * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle 1141573Srgrimes * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If 1151573Srgrimes * this routine is heavily used enough, it's worth the ugly coding. 1161573Srgrimes * 1171573Srgrimes * OZ's original sdbm hash 1181573Srgrimes */ 1191573Srgrimesstatic u_int32_t 1201573Srgrimeshash3(keyarg, len) 1211573Srgrimes const void *keyarg; 12292889Sobrien size_t len; 1231573Srgrimes{ 12492889Sobrien const u_char *key; 12592889Sobrien size_t loop; 12692889Sobrien u_int32_t h; 1271573Srgrimes 1281573Srgrimes#define HASHC h = *key++ + 65599 * h 1291573Srgrimes 1301573Srgrimes h = 0; 1311573Srgrimes key = keyarg; 1321573Srgrimes if (len > 0) { 1331573Srgrimes loop = (len + 8 - 1) >> 3; 1341573Srgrimes 1351573Srgrimes switch (len & (8 - 1)) { 1361573Srgrimes case 0: 1371573Srgrimes do { 1381573Srgrimes HASHC; 1391573Srgrimes /* FALLTHROUGH */ 1401573Srgrimes case 7: 1411573Srgrimes HASHC; 1421573Srgrimes /* FALLTHROUGH */ 1431573Srgrimes case 6: 1441573Srgrimes HASHC; 1451573Srgrimes /* FALLTHROUGH */ 1461573Srgrimes case 5: 1471573Srgrimes HASHC; 1481573Srgrimes /* FALLTHROUGH */ 1491573Srgrimes case 4: 1501573Srgrimes HASHC; 1511573Srgrimes /* FALLTHROUGH */ 1521573Srgrimes case 3: 1531573Srgrimes HASHC; 1541573Srgrimes /* FALLTHROUGH */ 1551573Srgrimes case 2: 1561573Srgrimes HASHC; 1571573Srgrimes /* FALLTHROUGH */ 1581573Srgrimes case 1: 1591573Srgrimes HASHC; 1601573Srgrimes } while (--loop); 1611573Srgrimes } 1621573Srgrimes } 1631573Srgrimes return (h); 1641573Srgrimes} 1651573Srgrimes 1661573Srgrimes/* Hash function from Chris Torek. */ 1671573Srgrimesstatic u_int32_t 1681573Srgrimeshash4(keyarg, len) 1691573Srgrimes const void *keyarg; 17092889Sobrien size_t len; 1711573Srgrimes{ 17292889Sobrien const u_char *key; 17392889Sobrien size_t loop; 17492889Sobrien u_int32_t h; 1751573Srgrimes 1761573Srgrimes#define HASH4a h = (h << 5) - h + *key++; 1771573Srgrimes#define HASH4b h = (h << 5) + h + *key++; 1781573Srgrimes#define HASH4 HASH4b 1791573Srgrimes 1801573Srgrimes h = 0; 1811573Srgrimes key = keyarg; 1821573Srgrimes if (len > 0) { 1831573Srgrimes loop = (len + 8 - 1) >> 3; 1841573Srgrimes 1851573Srgrimes switch (len & (8 - 1)) { 1861573Srgrimes case 0: 1871573Srgrimes do { 1881573Srgrimes HASH4; 1891573Srgrimes /* FALLTHROUGH */ 1901573Srgrimes case 7: 1911573Srgrimes HASH4; 1921573Srgrimes /* FALLTHROUGH */ 1931573Srgrimes case 6: 1941573Srgrimes HASH4; 1951573Srgrimes /* FALLTHROUGH */ 1961573Srgrimes case 5: 1971573Srgrimes HASH4; 1981573Srgrimes /* FALLTHROUGH */ 1991573Srgrimes case 4: 2001573Srgrimes HASH4; 2011573Srgrimes /* FALLTHROUGH */ 2021573Srgrimes case 3: 2031573Srgrimes HASH4; 2041573Srgrimes /* FALLTHROUGH */ 2051573Srgrimes case 2: 2061573Srgrimes HASH4; 2071573Srgrimes /* FALLTHROUGH */ 2081573Srgrimes case 1: 2091573Srgrimes HASH4; 2101573Srgrimes } while (--loop); 2111573Srgrimes } 2121573Srgrimes } 2131573Srgrimes return (h); 2141573Srgrimes} 215