mfbt/PairHash.h

   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 /* Utilities for hashing pairs. */
   8
   9 #ifndef mozilla_PairHash_h
  10 #define mozilla_PairHash_h
  11
  12 #include "mozilla/CompactPair.h"
  13 #include "mozilla/HashFunctions.h"
  14
  15 #include <utility>  // std::pair
  16
  17 namespace mozilla {
  18
  19 /**
  20  * The HashPair overloads below do just what you'd expect.
  21  *
  22  * These functions support hash of std::pair<T,U> and mozilla::CompactPair<T,u>
  23  * where type T and U both support AddToHash.
  24  */
  25 template <typename U, typename V>
  26 [[nodiscard]] inline HashNumber HashPair(const std::pair<U, V>& pair) {
  27   // Pair hash combines the hash of each member
  28   return HashGeneric(pair.first, pair.second);
  29 }
  30
  31 template <typename U, typename V>
  32 [[nodiscard]] inline HashNumber HashCompactPair(const CompactPair<U, V>& pair) {
  33   // Pair hash combines the hash of each member
  34   return HashGeneric(pair.first(), pair.second());
  35 }
  36
  37 /**
  38  * Hash policy for std::pair compatible with HashTable
  39  */
  40 template <typename T, typename U>
  41 struct PairHasher {
  42   using Key = std::pair<T, U>;
  43   using Lookup = Key;
  44
  45   static HashNumber hash(const Lookup& aLookup) { return HashPair(aLookup); }
  46
  47   static bool match(const Key& aKey, const Lookup& aLookup) {
  48     return aKey == aLookup;
  49   }
  50
  51   static void rekey(Key& aKey, const Key& aNewKey) { aKey = aNewKey; }
  52 };
  53
  54 /**
  55  * Hash policy for mozilla::CompactPair compatible with HashTable
  56  */
  57 template <typename T, typename U>
  58 struct CompactPairHasher {
  59   using Key = CompactPair<T, U>;
  60   using Lookup = Key;
  61
  62   static HashNumber hash(const Lookup& aLookup) {
  63     return HashCompactPair(aLookup);
  64   }
  65
  66   static bool match(const Key& aKey, const Lookup& aLookup) {
  67     return aKey == aLookup;
  68   }
  69
  70   static void rekey(Key& aKey, const Key& aNewKey) { aKey = aNewKey; }
  71 };
  72
  73 }  // namespace mozilla
  74
  75 #endif /* mozilla_PairHash_h */