NetBSD/lib/libc/db/hash/hfunc.c

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1993-03-21 12:45:37 +03:00
/*-
* Copyright (c) 1990 The Regents of the University of California.
* All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Margo Seltzer.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)hfunc.c 5.1 (Berkeley) 2/12/91";
#endif /* LIBC_SCCS and not lint */
/* Global default hash function */
static int hash1();
static int hash2();
static int hash3();
static int hash4();
int (*default_hash)() = hash4;
/******************************* HASH FUNCTIONS **************************/
/*
Assume that we've already split the bucket to which this
key hashes, calculate that bucket, and check that in fact
we did already split it.
This came from ejb's hsearch.
*/
# define PRIME1 37
# define PRIME2 1048583
static int
hash1(key,len)
char *key;
int len;
{
register int h;
register int l = len;
register unsigned char *k = (unsigned char *) key;
h = 0;
/*
* Convert string to integer
*/
while (l--) h = h * PRIME1 ^ (*k++ - ' ');
h %= PRIME2;
return (h);
}
/*
Phong's linear congruential hash
*/
#define dcharhash(h, c) ((h) = 0x63c63cd9*(h) + 0x9c39c33d + (c))
static int
hash2(str, n)
register unsigned char *str;
int n;
{
register unsigned char *e, c;
register int h;
e = str + n;
for (h = 0; str != e;) {
c = *str++;
if (!c && str > e)
break;
dcharhash(h,c);
}
return(h);
}
/*
* This is INCREDIBLY ugly, but fast.
* We break the string up into 8 byte units. On the first time
* through the loop we get the "leftover bytes" (strlen % 8).
* On every other iteration, we perform 8 HASHC's so we handle
* all 8 bytes. Essentially, this saves us 7 cmp & branch
* instructions. If this routine is heavily used enough, it's
* worth the ugly coding
*
* OZ's original sdbm hash
*/
static int
hash3(key,nbytes)
char *key;
int nbytes;
{
register int n = 0;
register char *str = key;
register int loop;
register int len = nbytes;
#define HASHC n = *str++ + 65599 * n
if (len > 0) {
loop = (len + 8 - 1) >> 3;
switch(len & (8 - 1)) {
case 0: do { /* All fall throughs */
HASHC;
case 7: HASHC;
case 6: HASHC;
case 5: HASHC;
case 4: HASHC;
case 3: HASHC;
case 2: HASHC;
case 1: HASHC;
} while (--loop);
}
}
return(n);
}
/* Hash function from Chris Torek */
static int
hash4(key,nbytes)
char *key;
int nbytes;
{
register int h = 0;
register char *p = key;
register int loop;
register int len = nbytes;
#define HASH4a h = (h << 5) - h + *p++;
#define HASH4b h = (h << 5) + h + *p++;
#define HASH4 HASH4b
if (len > 0) {
loop = (len + 8 - 1) >> 3;
switch(len & (8 - 1)) {
case 0: do { /* All fall throughs */
HASH4;
case 7: HASH4;
case 6: HASH4;
case 5: HASH4;
case 4: HASH4;
case 3: HASH4;
case 2: HASH4;
case 1: HASH4;
} while (--loop);
}
}
return(h);
}