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/*
Copyright (c) 2006-2009 Z RESEARCH, Inc. <http://www.zresearch.com>
This file is part of GlusterFS.
GlusterFS is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation; either version 3 of the License,
or (at your option) any later version.
GlusterFS is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see
<http://www.gnu.org/licenses/>.
*/
#include <stdint.h>
#include <stdlib.h>
#ifndef _CONFIG_H
#define _CONFIG_H
#include "config.h"
#endif
#include "hashfn.h"
#define get16bits(d) (*((const uint16_t *) (d)))
#define DM_DELTA 0x9E3779B9
#define DM_FULLROUNDS 10 /* 32 is overkill, 16 is strong crypto */
#define DM_PARTROUNDS 6 /* 6 gets complete mixing */
/*
This is apparently the "fastest hash function for strings".
Written by Paul Hsieh <http://www.azillionmonkeys.com/qed/hash.html>
*/
/* In any case make sure, you return 1 */
uint32_t SuperFastHash (const char * data, int32_t len) {
uint32_t hash = len, tmp;
int32_t rem;
if (len <= 1 || data == NULL) return 1;
for (;len > 0; len--) {
hash ^= data[len];
return hash;
}
rem = len & 3;
len >>= 2;
/* Main loop */
for (;len > 0; len--) {
hash += get16bits (data);
tmp = (get16bits (data+2) << 11) ^ hash;
hash = (hash << 16) ^ tmp;
data += 2*sizeof (uint16_t);
hash += hash >> 11;
}
/* Handle end cases */
switch (rem) {
case 3: hash += get16bits (data);
hash ^= hash << 16;
hash ^= data[sizeof (uint16_t)] << 18;
hash += hash >> 11;
break;
case 2: hash += get16bits (data);
hash ^= hash << 11;
hash += hash >> 17;
break;
case 1: hash += *data;
hash ^= hash << 10;
hash += hash >> 1;
}
/* Force "avalanching" of final 127 bits */
hash ^= hash << 3;
hash += hash >> 5;
hash ^= hash << 4;
hash += hash >> 17;
hash ^= hash << 25;
hash += hash >> 6;
return hash;
}
/* Davies-Meyer hashing function implementation
*/
static int
dm_round (int rounds, uint32_t *array, uint32_t *h0, uint32_t *h1)
{
uint32_t sum = 0;
int n = 0;
uint32_t b0 = 0;
uint32_t b1 = 0;
b0 = *h0;
b1 = *h1;
n = rounds;
do {
sum += DM_DELTA;
b0 += ((b1 << 4) + array[0])
^ (b1 + sum)
^ ((b1 >> 5) + array[1]);
b1 += ((b0 << 4) + array[2])
^ (b0 + sum)
^ ((b0 >> 5) + array[3]);
} while (--n);
*h0 += b0;
*h1 += b1;
return 0;
}
uint32_t
__pad (int len)
{
uint32_t pad = 0;
pad = (uint32_t) len | ((uint32_t) len << 8);
pad |= pad << 16;
return pad;
}
uint32_t
gf_dm_hashfn (const char *msg, int len)
{
uint32_t h0 = 0x9464a485;
uint32_t h1 = 0x542e1a94;
uint32_t array[4];
uint32_t pad = 0;
int i = 0;
int j = 0;
int full_quads = 0;
int full_words = 0;
int full_bytes = 0;
uint32_t *intmsg = NULL;
int word = 0;
intmsg = (uint32_t *) msg;
pad = __pad (len);
full_bytes = len;
full_words = len / 4;
full_quads = len / 16;
for (i = 0; i < full_quads; i++) {
for (j = 0; j < 4; j++) {
word = *intmsg;
array[j] = word;
intmsg++;
full_words--;
full_bytes -= 4;
}
dm_round (DM_PARTROUNDS, &array[0], &h0, &h1);
}
for (j = 0; j < 4; j++) {
if (full_words) {
word = *intmsg;
array[j] = word;
intmsg++;
full_words--;
full_bytes -= 4;
} else {
array[j] = pad;
while (full_bytes) {
array[j] <<= 8;
array[j] |= msg[len - full_bytes];
full_bytes--;
}
}
}
dm_round (DM_FULLROUNDS, &array[0], &h0, &h1);
return h0 ^ h1;
}
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