layout/style/nsNthIndexCache.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5 #ifndef nsContentIndexCache_h__
   6 #define nsContentIndexCache_h__
   7
   8 #include "js/HashTable.h"
   9
  10 class nsIContent;
  11
  12 namespace mozilla {
  13 namespace dom {
  14 class Element;
  15 } // namespace dom
  16 } // namespace mozilla
  17
  18 /*
  19  * A class that computes and caches the indices used for :nth-* pseudo-class
  20  * matching.
  21  */
  22
  23 class nsNthIndexCache {
  24 private:
  25   typedef mozilla::dom::Element Element;
  26
  27 public:
  28   /**
  29    * Constructor and destructor out of line so that we don't try to
  30    * instantiate the hashtable template all over the place.
  31    */
  32   nsNthIndexCache();
  33   ~nsNthIndexCache();
  34
  35   // Returns a 1-based index of the child in its parent.  If the child
  36   // is not in its parent's child list (i.e., it is anonymous content),
  37   // returns 0.
  38   // If aCheckEdgeOnly is true, the function will return 1 if the result
  39   // is 1, and something other than 1 (maybe or maybe not a valid
  40   // result) otherwise.
  41   // This must only be called on nodes which have a non-null parent.
  42   int32_t GetNthIndex(Element* aChild, bool aIsOfType, bool aIsFromEnd,
  43                       bool aCheckEdgeOnly);
  44
  45   void Reset();
  46
  47 private:
  48   /**
  49    * Returns true if aSibling and aElement should be considered in the same
  50    * list for nth-index purposes, taking aIsOfType into account.
  51    */
  52   inline bool SiblingMatchesElement(nsIContent* aSibling, Element* aElement,
  53                                     bool aIsOfType);
  54
  55   // This node's index for this cache.
  56   // If -2, needs to be computed.
  57   // If -1, needs to be computed but known not to be 1.
  58   // If 0, the node is not at any index in its parent.
  59   typedef int32_t CacheEntry;
  60
  61   class SystemAllocPolicy {
  62   public:
  63     void *malloc_(size_t bytes) { return ::malloc(bytes); }
  64
  65     template <typename T>
  66     T *pod_calloc(size_t numElems) {
  67       return static_cast<T *>(::calloc(numElems, sizeof(T)));
  68     }
  69
  70     void *realloc_(void *p, size_t bytes) { return ::realloc(p, bytes); }
  71     void free_(void *p) { ::free(p); }
  72     void reportAllocOverflow() const {}
  73   };
  74
  75   typedef js::HashMap<nsIContent*, CacheEntry, js::DefaultHasher<nsIContent*>,
  76                       SystemAllocPolicy> Cache;
  77
  78   /**
  79    * Returns true if aResult has been set to the correct value for aChild and
  80    * no more work needs to be done.  Returns false otherwise.
  81    *
  82    * aResult is an inout parameter.  The in value is the number of elements
  83    * that are in the half-open range (aSibling, aChild] (so including aChild
  84    * but not including aSibling) that match aChild.  The out value is the
  85    * correct index for aChild if this function returns true and the number of
  86    * elements in the closed range [aSibling, aChild] that match aChild
  87    * otherwise.
  88    */
  89   inline bool IndexDeterminedFromPreviousSibling(nsIContent* aSibling,
  90                                                  Element* aChild,
  91                                                  bool aIsOfType,
  92                                                  bool aIsFromEnd,
  93                                                  const Cache& aCache,
  94                                                  int32_t& aResult);
  95
  96   // Caches of indices for :nth-child(), :nth-last-child(),
  97   // :nth-of-type(), :nth-last-of-type(), keyed by Element*.
  98   //
  99   // The first subscript is 0 for -child and 1 for -of-type, the second
 100   // subscript is 0 for nth- and 1 for nth-last-.
 101   Cache mCaches[2][2];
 102 };
 103
 104 #endif /* nsContentIndexCache_h__ */