/*
 *  hashcompare.c -- Comparison functions for hash access method.
 *
 *	These functions are stored in pg_amproc.  For each operator class
 *	defined on hash tables, they compute the hash value of the argument.
 *
 */

#include "tmp/c.h"
#include "tmp/postgres.h"
#include "utils/nabstime.h"

RcsId("$Header: /private/src/postgres/src/backend/access/hash/RCS/hashfunc.c,v 1.2 1993/10/02 02:44:53 kristin Exp $");

uint32
hashint2(key)
    int16 key;
{
    return ((uint32) ~key);
}

uint32
hashint4(key)
    uint32 key;
{
    return (~key);
}

/* Hash function from Chris Torek. */
uint32
hashfloat4(keyp)
    float32 keyp;
{
    int len;
    int loop;
    uint32 h;

    len = sizeof(float32data);

#define HASH4a   h = (h << 5) - h + *keyp++;
#define HASH4b   h = (h << 5) + h + *keyp++;
#define HASH4 HASH4b


    h = 0;
    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);
}	


uint32
hashfloat8(keyp)
    float64 keyp;
{
    int len;
    int loop;
    uint32 h;

    len = sizeof(float64data);

#define HASH4a   h = (h << 5) - h + *keyp++;
#define HASH4b   h = (h << 5) + h + *keyp++;
#define HASH4 HASH4b


    h = 0;
    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);
}	


uint32
hashoid(key)
    ObjectId key;
{
    return ((uint32) ~key);
}


uint32
hashchar(key)
    char key;
{
    int len;
    uint32 h;

    len = sizeof(char);

#define PRIME1		37
#define PRIME2		1048583

    h = 0;
    /* Convert char to integer */
    h = h * PRIME1 ^ (key - ' ');
    h %= PRIME2;
    
    return (h);
}

uint32
hashchar16(key)
    char *key;
{
    uint32 h;
    int len;
 
    h = 0;
    len = sizeof(char16);
    /* Convert string to integer */
    while (len--)
	h = h * PRIME1 ^ (*key++ - ' ');
    h %= PRIME2;
	
    return (h);
}


/*
 * (Comment from the original db3 hashing code: )
 *
 * "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"
 */
uint32
hashtext(key)
    struct varlena *key;
{
    int keylen;
    char *keydata;
    uint32 n;
    int loop;

    keydata = VARDATA(key);
    keylen = VARSIZE(key);

    /* keylen includes the four bytes in which string keylength is stored */
    keylen -= sizeof(VARSIZE(key));

#define HASHC   n = *keydata++ + 65599 * n

    n = 0;
    if (keylen > 0) {
	loop = (keylen + 8 - 1) >> 3;
	
	switch (keylen & (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);
}