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/* $Id: strhash.h $ */
/** @file
* IPRT - Internal header containing inline string hashing functions.
*/
/*
* Copyright (C) 2006-2020 Oracle Corporation
*
* This file is part of VirtualBox Open Source Edition (OSE), as
* available from http://www.virtualbox.org. This file is free software;
* you can redistribute it and/or modify it under the terms of the GNU
* General Public License (GPL) as published by the Free Software
* Foundation, in version 2 as it comes in the "COPYING" file of the
* VirtualBox OSE distribution. VirtualBox OSE is distributed in the
* hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
*
* The contents of this file may alternatively be used under the terms
* of the Common Development and Distribution License Version 1.0
* (CDDL) only, as it comes in the "COPYING.CDDL" file of the
* VirtualBox OSE distribution, in which case the provisions of the
* CDDL are applicable instead of those of the GPL.
*
* You may elect to license modified versions of this file under the
* terms and conditions of either the GPL or the CDDL or both.
*/
#ifndef IPRT_INCLUDED_INTERNAL_strhash_h
#define IPRT_INCLUDED_INTERNAL_strhash_h
#ifndef RT_WITHOUT_PRAGMA_ONCE
# pragma once
#endif
#include <iprt/types.h>
/* sdbm:
This algorithm was created for sdbm (a public-domain reimplementation of
ndbm) database library. it was found to do well in scrambling bits,
causing better distribution of the keys and fewer splits. it also happens
to be a good general hashing function with good distribution. the actual
function is hash(i) = hash(i - 1) * 65599 + str[i]; what is included below
is the faster version used in gawk. [there is even a faster, duff-device
version] the magic constant 65599 was picked out of thin air while
experimenting with different constants, and turns out to be a prime.
this is one of the algorithms used in berkeley db (see sleepycat) and
elsewhere. */
/**
* Hash string, return hash + length.
*/
DECLINLINE(uint32_t) sdbm(const char *str, size_t *pcch)
{
uint8_t *pu8 = (uint8_t *)str;
uint32_t hash = 0;
int c;
while ((c = *pu8++))
hash = c + (hash << 6) + (hash << 16) - hash;
*pcch = (uintptr_t)pu8 - (uintptr_t)str - 1;
return hash;
}
/**
* Hash up to N bytes, return hash + hashed length.
*/
DECLINLINE(uint32_t) sdbmN(const char *str, size_t cchMax, size_t *pcch)
{
uint8_t *pu8 = (uint8_t *)str;
uint32_t hash = 0;
int c;
while ((c = *pu8++) && cchMax-- > 0)
hash = c + (hash << 6) + (hash << 16) - hash;
*pcch = (uintptr_t)pu8 - (uintptr_t)str - 1;
return hash;
}
/**
* Incremental hashing.
*/
DECLINLINE(uint32_t) sdbmInc(const char *str, uint32_t hash)
{
uint8_t *pu8 = (uint8_t *)str;
int c;
while ((c = *pu8++))
hash = c + (hash << 6) + (hash << 16) - hash;
return hash;
}
/**
* Incremental hashing with length limitation.
*/
DECLINLINE(uint32_t) sdbmIncN(const char *psz, size_t cchMax, uint32_t uHash)
{
uint8_t *pu8 = (uint8_t *)psz;
int c;
while ((c = *pu8++) && cchMax-- > 0)
uHash = c + (uHash << 6) + (uHash << 16) - uHash;
return uHash;
}
#endif /* !IPRT_INCLUDED_INTERNAL_strhash_h */
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