postgresql/src/backend/utils/hash/hashfn.c

/*-------------------------------------------------------------------------
 *
 * hashfn.c--
 *    
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /cvsroot/pgsql/src/backend/utils/hash/hashfn.c,v 1.1.1.1 1996/07/09 06:22:08 scrappy Exp $
 *
 *-------------------------------------------------------------------------
 */
#include <string.h>
#include "utils/hsearch.h"

/*
 * 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.
 */
long
string_hash(char *key, int keysize)
{
    int h;
    register unsigned char *k = (unsigned char *) key;
    
    h = 0;
    /*
     * Convert string to integer
     */
    while (*k)
	h = h * PRIME1 ^ (*k++ - ' ');
    h %= PRIME2;
    
    return (h);
}


long
tag_hash(int *key, int keysize)
{
    register long h = 0;
    
    /*
     * Convert tag to integer;  Use four byte chunks in a "jump table"
     * to go a little faster.  Currently the maximum keysize is 16
     * (mar 17 1992) I have put in cases for up to 24.  Bigger than
     * this will resort to the old behavior of the for loop. (see the
     * default case).
     */
    switch (keysize)
	{
	case 6*sizeof(int):
	    h = h * PRIME1 ^ (*key);
	    key++;
	    /* fall through */
	    
	case 5*sizeof(int):
	    h = h * PRIME1 ^ (*key);
	    key++;
	    /* fall through */
	    
	case 4*sizeof(int):
	    h = h * PRIME1 ^ (*key);
	    key++;
	    /* fall through */
	    
	case 3*sizeof(int):
	    h = h * PRIME1 ^ (*key);
	    key++;
	    /* fall through */
	    
	case 2*sizeof(int):
	    h = h * PRIME1 ^ (*key);
	    key++;
	    /* fall through */
	    
	case sizeof(int):
	    h = h * PRIME1 ^ (*key);
	    key++;
	    break;
	    
	default:
	    for(; keysize > (sizeof(int)-1); keysize -= sizeof(int), key++)
		h = h * PRIME1 ^ (*key);
	    /*
	     * now let's grab the last few bytes of the tag if the tag
	     * has (size % 4) != 0 (which it sometimes will on a sun3).
	     */
	    if (keysize)
		{
		    char *keytmp = (char *)key;
		    
		    switch (keysize)
			{
			case 3:
			    h = h * PRIME1 ^ (*keytmp);
			    keytmp++;
			    /* fall through */
			case 2:
			    h = h * PRIME1 ^ (*keytmp);
			    keytmp++;
			    /* fall through */
			case 1:
			    h = h * PRIME1 ^ (*keytmp);
			    break;
			}
		}
	    break;
	}
    
    h %= PRIME2;
    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
 */
long
disk_hash(char *key)
{
    register int n = 0;
    register char *str = key;
    register int len = strlen(key);
    register int loop;
    
#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);
}