1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 /* This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6
7 /* Helper routines for perfecthash.py. Not to be used directly. */
8
9 #ifndef mozilla_PerfectHash_h
10 #define mozilla_PerfectHash_h
11
12 #include <type_traits>
13
14 namespace mozilla {
15 namespace perfecthash {
16
17 // 32-bit FNV offset basis and prime value.
18 // NOTE: Must match values in |perfecthash.py|
19 constexpr uint32_t FNV_OFFSET_BASIS = 0x811C9DC5;
20 constexpr uint32_t FNV_PRIME = 16777619;
21
22 /**
23 * Basic FNV hasher function used by perfecthash. Generic over the unit type.
24 */
25 template <typename C>
Hash(uint32_t aBasis,const C * aKey,size_t aLen)26 inline uint32_t Hash(uint32_t aBasis, const C* aKey, size_t aLen) {
27 for (size_t i = 0; i < aLen; ++i) {
28 aBasis =
29 (aBasis ^ static_cast<std::make_unsigned_t<C>>(aKey[i])) * FNV_PRIME;
30 }
31 return aBasis;
32 }
33
34 /**
35 * Helper method for getting the index from a perfect hash.
36 * Called by code generated from |perfecthash.py|.
37 */
38 template <typename C, typename Base, size_t NBases, typename Entry,
39 size_t NEntries>
Lookup(const C * aKey,size_t aLen,const Base (& aTable)[NBases],const Entry (& aEntries)[NEntries])40 inline const Entry& Lookup(const C* aKey, size_t aLen,
41 const Base (&aTable)[NBases],
42 const Entry (&aEntries)[NEntries]) {
43 uint32_t basis = aTable[Hash(FNV_OFFSET_BASIS, aKey, aLen) % NBases];
44 return aEntries[Hash(basis, aKey, aLen) % NEntries];
45 }
46
47 } // namespace perfecthash
48 } // namespace mozilla
49
50 #endif // !defined(mozilla_PerfectHash_h)
51