JavaScriptCore/runtime/SmallStrings.cpp

   1 /*
   2  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "config.h"
  27 #include "SmallStrings.h"
  28
  29 #include "JSGlobalObject.h"
  30 #include "JSString.h"
  31
  32 #include <wtf/Noncopyable.h>
  33
  34 namespace JSC {
  35 static const unsigned numCharactersToStore = 0x100;
  36
  37 class SmallStringsStorage : public Noncopyable {
  38 public:
  39     SmallStringsStorage();
  40
  41     UString::Rep* rep(unsigned char character) { return &m_reps[character]; }
  42
  43 private:
  44     UChar m_characters[numCharactersToStore];
  45     UString::BaseString m_base;
  46     UString::Rep m_reps[numCharactersToStore];
  47 };
  48
  49 SmallStringsStorage::SmallStringsStorage()
  50     : m_base(m_characters, numCharactersToStore)
  51 {
  52     m_base.rc = numCharactersToStore + 1;
  53     // make sure UString doesn't try to reuse the buffer by pretending we have one more character in it
  54     m_base.usedCapacity = numCharactersToStore + 1;
  55     m_base.capacity = numCharactersToStore + 1;
  56     m_base.checkConsistency();
  57
  58     for (unsigned i = 0; i < numCharactersToStore; ++i)
  59         m_characters[i] = i;
  60
  61     memset(&m_reps, 0, sizeof(m_reps));
  62     for (unsigned i = 0; i < numCharactersToStore; ++i) {
  63         m_reps[i].offset = i;
  64         m_reps[i].len = 1;
  65         m_reps[i].rc = 1;
  66         m_reps[i].setBaseString(&m_base);
  67         m_reps[i].checkConsistency();
  68     }
  69 }
  70
  71 SmallStrings::SmallStrings()
  72     : m_emptyString(0)
  73     , m_storage(0)
  74 {
  75     COMPILE_ASSERT(numCharactersToStore == sizeof(m_singleCharacterStrings) / sizeof(m_singleCharacterStrings[0]), IsNumCharactersConstInSyncWithClassUsage);
  76
  77     for (unsigned i = 0; i < numCharactersToStore; ++i)
  78         m_singleCharacterStrings[i] = 0;
  79 }
  80
  81 SmallStrings::~SmallStrings()
  82 {
  83 }
  84
  85 void SmallStrings::markChildren(MarkStack& markStack)
  86 {
  87     if (m_emptyString)
  88         markStack.append(m_emptyString);
  89     for (unsigned i = 0; i < numCharactersToStore; ++i) {
  90         if (m_singleCharacterStrings[i])
  91             markStack.append(m_singleCharacterStrings[i]);
  92     }
  93 }
  94
  95 unsigned SmallStrings::count() const
  96 {
  97     unsigned count = 0;
  98     if (m_emptyString)
  99         ++count;
 100     for (unsigned i = 0; i < numCharactersToStore; ++i) {
 101         if (m_singleCharacterStrings[i])
 102             ++count;
 103     }
 104     return count;
 105 }
 106
 107 void SmallStrings::createEmptyString(JSGlobalData* globalData)
 108 {
 109     ASSERT(!m_emptyString);
 110     m_emptyString = new (globalData) JSString(globalData, "", JSString::HasOtherOwner);
 111 }
 112
 113 void SmallStrings::createSingleCharacterString(JSGlobalData* globalData, unsigned char character)
 114 {
 115     if (!m_storage)
 116         m_storage.set(new SmallStringsStorage);
 117     ASSERT(!m_singleCharacterStrings[character]);
 118     m_singleCharacterStrings[character] = new (globalData) JSString(globalData, m_storage->rep(character), JSString::HasOtherOwner);
 119 }
 120
 121 UString::Rep* SmallStrings::singleCharacterStringRep(unsigned char character)
 122 {
 123     if (!m_storage)
 124         m_storage.set(new SmallStringsStorage);
 125     return m_storage->rep(character);
 126 }
 127
 128 } // namespace JSC