js/src/ds/FixedSizeHash.h@6474c204b198 (annotated)
js/src/ds/FixedSizeHash.h
Wed, 31 Dec 2014 06:09:35 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Wed, 31 Dec 2014 06:09:35 +0100
- changeset 0
- 6474c204b198
- permissions
- -rw-r--r--
Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.
| michael@0 | 1 | /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- |
| michael@0 | 2 | * vim: set ts=8 sts=4 et sw=4 tw=99: |
| michael@0 | 3 | * This Source Code Form is subject to the terms of the Mozilla Public |
| michael@0 | 4 | * License, v. 2.0. If a copy of the MPL was not distributed with this |
| michael@0 | 5 | * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ |
| michael@0 | 6 | |
| michael@0 | 7 | #ifndef jsfixedsizehash_h_ |
| michael@0 | 8 | #define jsfixedsizehash_h_ |
| michael@0 | 9 | |
| michael@0 | 10 | #include "ds/LifoAlloc.h" |
| michael@0 | 11 | |
| michael@0 | 12 | namespace js { |
| michael@0 | 13 | |
| michael@0 | 14 | /* |
| michael@0 | 15 | * Class representing a hash set with fixed capacity, with newer entries |
| michael@0 | 16 | * evicting older entries. Each entry has several hashes and can be stored in |
| michael@0 | 17 | * different buckets, with the choice of which to evict on insertion being |
| michael@0 | 18 | * managed via LRU. For tables with a relatively small size, using different |
| michael@0 | 19 | * hashes increases utilization and makes it less likely that entries will keep |
| michael@0 | 20 | * evicting each other due to wanting to use the same bucket. |
| michael@0 | 21 | * |
| michael@0 | 22 | * T indicates the type of hash elements, HashPolicy must have the following |
| michael@0 | 23 | * contents: |
| michael@0 | 24 | * |
| michael@0 | 25 | * Lookup - As for HashMap / HashSet. |
| michael@0 | 26 | * |
| michael@0 | 27 | * bool match(T, Lookup) - As for HashMap / HashSet. |
| michael@0 | 28 | * |
| michael@0 | 29 | * NumHashes - Number of different hashes generated for each entry. |
| michael@0 | 30 | * |
| michael@0 | 31 | * void hash(Lookup, HashNumber[NumHashes]) - Compute all hashes for an entry. |
| michael@0 | 32 | * |
| michael@0 | 33 | * void clear(T *) - Clear an entry, such that isCleared() holds afterwards. |
| michael@0 | 34 | * |
| michael@0 | 35 | * bool isCleared(T) - Test whether an entry has been cleared. |
| michael@0 | 36 | */ |
| michael@0 | 37 | template <class T, class HashPolicy, size_t Capacity> |
| michael@0 | 38 | class FixedSizeHashSet |
| michael@0 | 39 | { |
| michael@0 | 40 | T entries[Capacity]; |
| michael@0 | 41 | uint32_t lastOperations[Capacity]; |
| michael@0 | 42 | uint32_t numOperations; |
| michael@0 | 43 | |
| michael@0 | 44 | static const size_t NumHashes = HashPolicy::NumHashes; |
| michael@0 | 45 | |
| michael@0 | 46 | public: |
| michael@0 | 47 | typedef typename HashPolicy::Lookup Lookup; |
| michael@0 | 48 | |
| michael@0 | 49 | FixedSizeHashSet() |
| michael@0 | 50 | : entries(), lastOperations(), numOperations(0) |
| michael@0 | 51 | { |
| michael@0 | 52 | JS_STATIC_ASSERT(Capacity > 0); |
| michael@0 | 53 | JS_ASSERT(HashPolicy::isCleared(entries[0])); |
| michael@0 | 54 | } |
| michael@0 | 55 | |
| michael@0 | 56 | bool lookup(const Lookup &lookup, T *pentry) |
| michael@0 | 57 | { |
| michael@0 | 58 | size_t bucket; |
| michael@0 | 59 | if (lookupReference(lookup, &bucket)) { |
| michael@0 | 60 | *pentry = entries[bucket]; |
| michael@0 | 61 | lastOperations[bucket] = numOperations++; |
| michael@0 | 62 | return true; |
| michael@0 | 63 | } |
| michael@0 | 64 | return false; |
| michael@0 | 65 | } |
| michael@0 | 66 | |
| michael@0 | 67 | void insert(const Lookup &lookup, const T &entry) |
| michael@0 | 68 | { |
| michael@0 | 69 | size_t buckets[NumHashes]; |
| michael@0 | 70 | getBuckets(lookup, buckets); |
| michael@0 | 71 | |
| michael@0 | 72 | size_t min = buckets[0]; |
| michael@0 | 73 | for (size_t i = 0; i < NumHashes; i++) { |
| michael@0 | 74 | const T &entry = entries[buckets[i]]; |
| michael@0 | 75 | if (HashPolicy::isCleared(entry)) { |
| michael@0 | 76 | entries[buckets[i]] = entry; |
| michael@0 | 77 | lastOperations[buckets[i]] = numOperations++; |
| michael@0 | 78 | return; |
| michael@0 | 79 | } |
| michael@0 | 80 | if (i && lastOperations[min] > lastOperations[buckets[i]]) |
| michael@0 | 81 | min = buckets[i]; |
| michael@0 | 82 | } |
| michael@0 | 83 | |
| michael@0 | 84 | entries[min] = entry; |
| michael@0 | 85 | lastOperations[min] = numOperations++; |
| michael@0 | 86 | } |
| michael@0 | 87 | |
| michael@0 | 88 | template <typename S> |
| michael@0 | 89 | void remove(const S &s) |
| michael@0 | 90 | { |
| michael@0 | 91 | size_t bucket; |
| michael@0 | 92 | if (lookupReference(s, &bucket)) |
| michael@0 | 93 | HashPolicy::clear(&entries[bucket]); |
| michael@0 | 94 | } |
| michael@0 | 95 | |
| michael@0 | 96 | private: |
| michael@0 | 97 | template <typename S> |
| michael@0 | 98 | bool lookupReference(const S &s, size_t *pbucket) |
| michael@0 | 99 | { |
| michael@0 | 100 | size_t buckets[NumHashes]; |
| michael@0 | 101 | getBuckets(s, buckets); |
| michael@0 | 102 | |
| michael@0 | 103 | for (size_t i = 0; i < NumHashes; i++) { |
| michael@0 | 104 | const T &entry = entries[buckets[i]]; |
| michael@0 | 105 | if (!HashPolicy::isCleared(entry) && HashPolicy::match(entry, s)) { |
| michael@0 | 106 | *pbucket = buckets[i]; |
| michael@0 | 107 | return true; |
| michael@0 | 108 | } |
| michael@0 | 109 | } |
| michael@0 | 110 | |
| michael@0 | 111 | return false; |
| michael@0 | 112 | } |
| michael@0 | 113 | |
| michael@0 | 114 | template <typename S> |
| michael@0 | 115 | void getBuckets(const S &s, size_t buckets[NumHashes]) |
| michael@0 | 116 | { |
| michael@0 | 117 | HashNumber hashes[NumHashes]; |
| michael@0 | 118 | HashPolicy::hash(s, hashes); |
| michael@0 | 119 | |
| michael@0 | 120 | for (size_t i = 0; i < NumHashes; i++) |
| michael@0 | 121 | buckets[i] = hashes[i] % Capacity; |
| michael@0 | 122 | } |
| michael@0 | 123 | }; |
| michael@0 | 124 | |
| michael@0 | 125 | } /* namespace js */ |
| michael@0 | 126 | |
| michael@0 | 127 | #endif /* jsfixedsizehash_h_ */ |
