Ondřej Surý
b84c9b2608
Adding extra val & 0xffff in the isc_hash_bits32() macros in the hotpath has significantly reduced the performance. Turn the macro into static inline function matching the previous hash_32() function used to compute hashval matching the hashtable->bits.
93 lines
2.4 KiB
C
93 lines
2.4 KiB
C
/*
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* Copyright (C) Internet Systems Consortium, Inc. ("ISC")
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*
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* SPDX-License-Identifier: MPL-2.0
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, you can obtain one at https://mozilla.org/MPL/2.0/.
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*
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* See the COPYRIGHT file distributed with this work for additional
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* information regarding copyright ownership.
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*/
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#pragma once
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#include <inttypes.h>
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#include <stdbool.h>
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#include <isc/assertions.h>
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#include <isc/lang.h>
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#include <isc/types.h>
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#include <isc/util.h>
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#define ISC_HASHSIZE(bits) (UINT64_C(1) << (bits))
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#define ISC_HASH_OVERCOMMIT 3
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#define ISC_HASH_MIN_BITS 2U
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#define ISC_HASH_MAX_BITS 32U
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/***
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*** Functions
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***/
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ISC_LANG_BEGINDECLS
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const void *
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isc_hash_get_initializer(void);
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void
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isc_hash_set_initializer(const void *initializer);
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#define isc_hash_function isc_hash64
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uint32_t
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isc_hash32(const void *data, const size_t length, const bool case_sensitive);
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uint64_t
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isc_hash64(const void *data, const size_t length, const bool case_sensitive);
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/*!<
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* \brief Calculate a hash over data.
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*
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* This hash function is useful for hashtables. The hash function is
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* opaque and not important to the caller. The returned hash values are
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* non-deterministic and will have different mapping every time a
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* process using this library is run, but will have uniform
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* distribution.
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*
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* isc_hash_32/64() calculates the hash from start to end over the
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* input data.
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*
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* 'data' is the data to be hashed.
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*
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* 'length' is the size of the data to be hashed.
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*
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* 'case_sensitive' specifies whether the hash key should be treated as
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* case_sensitive values. It should typically be false if the hash key
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* is a DNS name.
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*
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* Returns:
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* \li 32 or 64-bit hash value
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*/
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/*!
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* \brief Return a hash value of a specified number of bits
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*
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* This function uses Fibonacci Hashing to convert a 32 bit hash value
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* 'val' into a smaller hash value of up to 'bits' bits. This results
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* in better hash table distribution than the use of modulo.
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*
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* Requires:
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* \li 'bits' is less than 32.
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*
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* Returns:
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* \li a hash value of length 'bits'.
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*/
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#define ISC_HASH_GOLDENRATIO_32 0x61C88647
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static inline uint32_t
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isc_hash_bits32(uint32_t val, unsigned int bits) {
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ISC_REQUIRE(bits <= ISC_HASH_MAX_BITS);
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/* High bits are more random. */
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return (val * ISC_HASH_GOLDENRATIO_32 >> (32 - bits));
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}
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ISC_LANG_ENDDECLS
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