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/*
* Copyright (c) 2008, 2009 Nicira Networks.
*
* 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"
/* This is the public domain lookup3 hash by Bob Jenkins from
* http://burtleburtle.net/bob/c/lookup3.c, modified for style. */
#define HASH_ROT(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
#define HASH_MIX(a, b, c) \
do { \
a -= c; a ^= HASH_ROT(c, 4); c += b; \
b -= a; b ^= HASH_ROT(a, 6); a += c; \
c -= b; c ^= HASH_ROT(b, 8); b += a; \
a -= c; a ^= HASH_ROT(c, 16); c += b; \
b -= a; b ^= HASH_ROT(a, 19); a += c; \
c -= b; c ^= HASH_ROT(b, 4); b += a; \
} while (0)
#define HASH_FINAL(a, b, c) \
do { \
c ^= b; c -= HASH_ROT(b, 14); \
a ^= c; a -= HASH_ROT(c, 11); \
b ^= a; b -= HASH_ROT(a, 25); \
c ^= b; c -= HASH_ROT(b, 16); \
a ^= c; a -= HASH_ROT(c, 4); \
b ^= a; b -= HASH_ROT(a, 14); \
c ^= b; c -= HASH_ROT(b, 24); \
} while (0)
uint32_t hash_words(const uint32_t *, size_t n_word, uint32_t basis);
uint32_t hash_2words(const uint32_t *, uint32_t basis);
uint32_t hash_bytes(const void *, size_t n_bytes, uint32_t basis);
static inline uint32_t hash_string(const char *s, uint32_t basis)
{
return hash_bytes(s, strlen(s), basis);
}
/* This is Bob Jenkins' integer hash from
* http://burtleburtle.net/bob/hash/integer.html, modified for style. */
static inline uint32_t hash_int(uint32_t x, uint32_t basis)
{
x -= x << 6;
x ^= x >> 17;
x -= x << 9;
x ^= x << 4;
x += basis;
x -= x << 3;
x ^= x << 10;
x ^= x >> 15;
return x;
}
/* 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)
{
enum { P0 = 0xc2b73583 }; /* This is hash_int(1, 0). */
enum { P1 = 0xe90f1258 }; /* This is hash_int(2, 0). */
return (x ? P0 : P1) ^ HASH_ROT(basis, 1);
}
static inline uint32_t hash_double(double x, uint32_t basis)
{
uint32_t value[2];
BUILD_ASSERT_DECL(sizeof x == sizeof value);
memcpy(value, &x, sizeof value);
return hash_2words(value, basis);
}
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);
}
#endif /* hash.h */
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