layout/style/nsNthIndexCache.cpp

   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
   6 /*
   7  * A class that computes and caches the indices used for :nth-* pseudo-class
   8  * matching.
   9  */
  10
  11 #include "nsNthIndexCache.h"
  12 #include "mozilla/dom/Element.h"
  13 #include "mozilla/dom/NodeInfoInlines.h"
  14
  15 nsNthIndexCache::nsNthIndexCache()
  16 {
  17 }
  18
  19 nsNthIndexCache::~nsNthIndexCache()
  20 {
  21 }
  22
  23 void
  24 nsNthIndexCache::Reset()
  25 {
  26   mCaches[0][0].clear();
  27   mCaches[0][1].clear();
  28   mCaches[1][0].clear();
  29   mCaches[1][1].clear();
  30 }
  31
  32 inline bool
  33 nsNthIndexCache::SiblingMatchesElement(nsIContent* aSibling, Element* aElement,
  34                                        bool aIsOfType)
  35 {
  36   return aSibling->IsElement() &&
  37     (!aIsOfType ||
  38      aSibling->NodeInfo()->NameAndNamespaceEquals(aElement->NodeInfo()));
  39 }
  40
  41 inline bool
  42 nsNthIndexCache::IndexDeterminedFromPreviousSibling(nsIContent* aSibling,
  43                                                     Element* aChild,
  44                                                     bool aIsOfType,
  45                                                     bool aIsFromEnd,
  46                                                     const Cache& aCache,
  47                                                     int32_t& aResult)
  48 {
  49   if (SiblingMatchesElement(aSibling, aChild, aIsOfType)) {
  50     Cache::Ptr siblingEntry = aCache.lookup(aSibling);
  51     if (siblingEntry) {
  52       int32_t siblingIndex = siblingEntry->value();
  53       NS_ASSERTION(siblingIndex != 0,
  54                    "How can a non-anonymous node have an anonymous sibling?");
  55       if (siblingIndex > 0) {
  56         // At this point, aResult is a count of how many elements matching
  57         // aChild we have seen after aSibling, including aChild itself.
  58         // |siblingIndex| is the index of aSibling.
  59         // So if aIsFromEnd, we want |aResult = siblingIndex - aResult| and
  60         // otherwise we want |aResult = siblingIndex + aResult|.
  61         aResult = siblingIndex + aResult * (1 - 2 * aIsFromEnd);
  62         return true;
  63       }
  64     }
  65
  66     ++aResult;
  67   }
  68
  69   return false;
  70 }
  71
  72 int32_t
  73 nsNthIndexCache::GetNthIndex(Element* aChild, bool aIsOfType,
  74                              bool aIsFromEnd, bool aCheckEdgeOnly)
  75 {
  76   NS_ASSERTION(aChild->GetParent(), "caller should check GetParent()");
  77
  78   if (aChild->IsRootOfAnonymousSubtree()) {
  79     return 0;
  80   }
  81
  82   Cache &cache = mCaches[aIsOfType][aIsFromEnd];
  83
  84   if (!cache.initialized() && !cache.init()) {
  85     // Give up and just don't match.
  86     return 0;
  87   }
  88
  89   Cache::AddPtr entry = cache.lookupForAdd(aChild);
  90
  91   // Default the value to -2 when adding
  92   if (!entry && !cache.add(entry, aChild, -2)) {
  93     // No good; don't match.
  94     return 0;
  95   }
  96
  97   int32_t &slot = entry->value();
  98   if (slot != -2 && (slot != -1 || aCheckEdgeOnly)) {
  99     return slot;
 100   }
 101
 102   int32_t result = 1;
 103   if (aCheckEdgeOnly) {
 104     // The caller only cares whether or not the result is 1, so we can
 105     // stop as soon as we see any other elements that match us.
 106     if (aIsFromEnd) {
 107       for (nsIContent *cur = aChild->GetNextSibling();
 108            cur;
 109            cur = cur->GetNextSibling()) {
 110         if (SiblingMatchesElement(cur, aChild, aIsOfType)) {
 111           result = -1;
 112           break;
 113         }
 114       }
 115     } else {
 116       for (nsIContent *cur = aChild->GetPreviousSibling();
 117            cur;
 118            cur = cur->GetPreviousSibling()) {
 119         if (SiblingMatchesElement(cur, aChild, aIsOfType)) {
 120           result = -1;
 121           break;
 122         }
 123       }
 124     }
 125   } else {
 126     // In the common case, we already have a cached index for one of
 127     // our previous siblings, so check that first.
 128     for (nsIContent *cur = aChild->GetPreviousSibling();
 129          cur;
 130          cur = cur->GetPreviousSibling()) {
 131       if (IndexDeterminedFromPreviousSibling(cur, aChild, aIsOfType,
 132                                              aIsFromEnd, cache, result)) {
 133         slot = result;
 134         return result;
 135       }
 136     }
 137
 138     // Now if aIsFromEnd we lose: need to actually compute our index,
 139     // since looking at previous siblings wouldn't have told us
 140     // anything about it.  Note that it doesn't make sense to do cache
 141     // lookups on our following siblings, since chances are the cache
 142     // is not primed for them.
 143     if (aIsFromEnd) {
 144       result = 1;
 145       for (nsIContent *cur = aChild->GetNextSibling();
 146            cur;
 147            cur = cur->GetNextSibling()) {
 148         if (SiblingMatchesElement(cur, aChild, aIsOfType)) {
 149           ++result;
 150         }
 151       }
 152     }
 153   }
 154
 155   slot = result;
 156   return result;
 157 }