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/*
* Copyright (c) 2008, 2009, 2010, 2012, 2013 Nicira, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef HASH_H
#define HASH_H 1
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include "util.h"
#ifdef __cplusplus
extern "C" {
#endif
static inline uint32_t
hash_rot(uint32_t x, int k)
{
return (x << k) | (x >> (32 - k));
}
uint32_t hash_words(const uint32_t data[], size_t n_words, uint32_t basis);
uint32_t hash_bytes(const void *, size_t n_bytes, uint32_t basis);
static inline uint32_t hash_int(uint32_t x, uint32_t basis);
static inline uint32_t hash_2words(uint32_t, uint32_t);
uint32_t hash_3words(uint32_t, uint32_t, uint32_t);
static inline uint32_t hash_boolean(bool x, uint32_t basis);
uint32_t hash_double(double, uint32_t basis);
static inline uint32_t hash_pointer(const void *, uint32_t basis);
static inline uint32_t hash_string(const char *, uint32_t basis);
/* Murmurhash by Austin Appleby,
* from http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp.
*
* The upstream license there says:
*
* // MurmurHash3 was written by Austin Appleby, and is placed in the public
* // domain. The author hereby disclaims copyright to this source code.
*
* See hash_words() for sample usage. */
static inline uint32_t mhash_add__(uint32_t hash, uint32_t data)
{
data *= 0xcc9e2d51;
data = hash_rot(data, 15);
data *= 0x1b873593;
return hash ^ data;
}
static inline uint32_t mhash_add(uint32_t hash, uint32_t data)
{
hash = mhash_add__(hash, data);
hash = hash_rot(hash, 13);
return hash * 5 + 0xe6546b64;
}
static inline uint32_t mhash_finish(uint32_t hash, size_t n_bytes)
{
hash ^= n_bytes;
hash ^= hash >> 16;
hash *= 0x85ebca6b;
hash ^= hash >> 13;
hash *= 0xc2b2ae35;
hash ^= hash >> 16;
return hash;
}
static inline uint32_t hash_string(const char *s, uint32_t basis)
{
return hash_bytes(s, strlen(s), basis);
}
static inline uint32_t hash_int(uint32_t x, uint32_t basis)
{
return hash_2words(x, basis);
}
/* An attempt at a useful 1-bit hash function. Has not been analyzed for
* quality. */
static inline uint32_t hash_boolean(bool x, uint32_t basis)
{
const uint32_t P0 = 0xc2b73583; /* This is hash_int(1, 0). */
const uint32_t P1 = 0xe90f1258; /* This is hash_int(2, 0). */
return (x ? P0 : P1) ^ hash_rot(basis, 1);
}
static inline uint32_t hash_pointer(const void *p, uint32_t basis)
{
/* Often pointers are hashed simply by casting to integer type, but that
* has pitfalls since the lower bits of a pointer are often all 0 for
* alignment reasons. It's hard to guess where the entropy really is, so
* we give up here and just use a high-quality hash function.
*
* The double cast suppresses a warning on 64-bit systems about casting to
* an integer to different size. That's OK in this case, since most of the
* entropy in the pointer is almost certainly in the lower 32 bits. */
return hash_int((uint32_t) (uintptr_t) p, basis);
}
static inline uint32_t hash_2words(uint32_t x, uint32_t y)
{
return mhash_finish(mhash_add(mhash_add(x, 0), y), 4);
}
#ifdef __cplusplus
}
#endif
#endif /* hash.h */
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