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/*
* Copyright (c) 2010-2014 Richard Braun.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*
* Hash functions for integers and strings.
*
* Integer hashing follows Thomas Wang's paper about his 32/64-bits mix
* functions :
* - https://gist.github.com/badboy/6267743
*
* String hashing uses a variant of the djb2 algorithm with k=31, as in
* the implementation of the hashCode() method of the Java String class :
* - http://www.javamex.com/tutorials/collections/hash_function_technical.shtml
*
* Note that this algorithm isn't suitable to obtain usable 64-bits hashes
* and is expected to only serve as an array index producer.
*
* These functions all have a bits parameter that indicates the number of
* relevant bits the caller is interested in. When returning a hash, its
* value must be truncated so that it can fit in the requested bit size.
* It can be used by the implementation to select high or low bits, depending
* on their relative randomness. To get complete, unmasked hashes, use the
* HASH_ALLBITS macro.
*/
#ifndef _HASH_H
#define _HASH_H
#include <stdint.h>
#ifdef __LP64__
#define HASH_ALLBITS 64
#define hash_long(n, bits) hash_int64(n, bits)
#else /* __LP64__ */
#define HASH_ALLBITS 32
#define hash_long(n, bits) hash_int32(n, bits)
#endif
static inline uint32_t
hash_int32(uint32_t n, unsigned int bits)
{
uint32_t hash;
hash = n;
hash = ~hash + (hash << 15);
hash ^= (hash >> 12);
hash += (hash << 2);
hash ^= (hash >> 4);
hash += (hash << 3) + (hash << 11);
hash ^= (hash >> 16);
return hash >> (32 - bits);
}
static inline uint64_t
hash_int64(uint64_t n, unsigned int bits)
{
uint64_t hash;
hash = n;
hash = ~hash + (hash << 21);
hash ^= (hash >> 24);
hash += (hash << 3) + (hash << 8);
hash ^= (hash >> 14);
hash += (hash << 2) + (hash << 4);
hash ^= (hash >> 28);
hash += (hash << 31);
return hash >> (64 - bits);
}
static inline unsigned long
hash_ptr(const void *ptr, unsigned int bits)
{
return hash_long((unsigned long)ptr, bits);
}
static inline unsigned long
hash_str(const char *str, unsigned int bits)
{
unsigned long hash;
char c;
for (hash = 0; (c = *str) != '\0'; str++)
hash = ((hash << 5) - hash) + c;
return hash & ((1 << bits) - 1);
}
#endif /* _HASH_H */
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