forked from mirrors/gecko-dev
1e4d8b891e
Differential Revision: https://phabricator.services.mozilla.com/D68358 --HG-- extra : moz-landing-system : lando
50 lines
1.6 KiB
C++
50 lines
1.6 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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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 http://mozilla.org/MPL/2.0/. */
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/* Helper routines for perfecthash.py. Not to be used directly. */
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#ifndef mozilla_PerfectHash_h
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#define mozilla_PerfectHash_h
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#include <type_traits>
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namespace mozilla {
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namespace perfecthash {
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// 32-bit FNV offset basis and prime value.
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// NOTE: Must match values in |perfecthash.py|
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constexpr uint32_t FNV_OFFSET_BASIS = 0x811C9DC5;
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constexpr uint32_t FNV_PRIME = 16777619;
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/**
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* Basic FNV hasher function used by perfecthash. Generic over the unit type.
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*/
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template <typename C>
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inline uint32_t Hash(uint32_t aBasis, const C* aKey, size_t aLen) {
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for (size_t i = 0; i < aLen; ++i) {
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aBasis =
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(aBasis ^ static_cast<std::make_unsigned_t<C>>(aKey[i])) * FNV_PRIME;
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}
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return aBasis;
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}
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/**
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* Helper method for getting the index from a perfect hash.
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* Called by code generated from |perfecthash.py|.
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*/
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template <typename C, typename Base, size_t NBases, typename Entry,
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size_t NEntries>
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inline const Entry& Lookup(const C* aKey, size_t aLen,
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const Base (&aTable)[NBases],
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const Entry (&aEntries)[NEntries]) {
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uint32_t basis = aTable[Hash(FNV_OFFSET_BASIS, aKey, aLen) % NBases];
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return aEntries[Hash(basis, aKey, aLen) % NEntries];
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}
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} // namespace perfecthash
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} // namespace mozilla
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#endif // !defined(mozilla_PerfectHash_h)
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