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 : 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 {
  51     for (unsigned i = 0; i < numCharactersToStore; ++i)
  52         m_characters[i] = i;
  53
  54     m_base.rc = numCharactersToStore + 1;
  55     m_base.buf = m_characters;
  56     m_base.len = numCharactersToStore;
  57     m_base.offset = 0;
  58     m_base._hash = 0;
  59     m_base.m_baseString = 0;
  60     m_base.preCapacity = 0;
  61     m_base.usedPreCapacity = 0;
  62     m_base.reportedCost = 0;
  63
  64     // make sure UString doesn't try to reuse the buffer by pretending we have one more character in it
  65     m_base.usedCapacity = numCharactersToStore + 1;
  66     m_base.capacity = numCharactersToStore + 1;
  67     m_base.checkConsistency();
  68
  69     memset(&m_reps, 0, sizeof(m_reps));
  70     for (unsigned i = 0; i < numCharactersToStore; ++i) {
  71         m_reps[i].offset = i;
  72         m_reps[i].len = 1;
  73         m_reps[i].rc = 1;
  74         m_reps[i].setBaseString(&m_base);
  75         m_reps[i].checkConsistency();
  76     }
  77 }
  78
  79 SmallStrings::SmallStrings()
  80     : m_emptyString(0)
  81     , m_storage(0)
  82 {
  83     COMPILE_ASSERT(numCharactersToStore == sizeof(m_singleCharacterStrings) / sizeof(m_singleCharacterStrings[0]), IsNumCharactersConstInSyncWithClassUsage);
  84
  85     for (unsigned i = 0; i < numCharactersToStore; ++i)
  86         m_singleCharacterStrings[i] = 0;
  87 }
  88
  89 SmallStrings::~SmallStrings()
  90 {
  91 }
  92
  93 void SmallStrings::mark()
  94 {
  95     if (m_emptyString && !m_emptyString->marked())
  96         m_emptyString->mark();
  97     for (unsigned i = 0; i < numCharactersToStore; ++i) {
  98         if (m_singleCharacterStrings[i] && !m_singleCharacterStrings[i]->marked())
  99             m_singleCharacterStrings[i]->mark();
 100     }
 101 }
 102
 103 unsigned SmallStrings::count() const
 104 {
 105     unsigned count = 0;
 106     if (m_emptyString)
 107         ++count;
 108     for (unsigned i = 0; i < numCharactersToStore; ++i) {
 109         if (m_singleCharacterStrings[i])
 110             ++count;
 111     }
 112     return count;
 113 }
 114
 115 void SmallStrings::createEmptyString(JSGlobalData* globalData)
 116 {
 117     ASSERT(!m_emptyString);
 118     m_emptyString = new (globalData) JSString(globalData, "", JSString::HasOtherOwner);
 119 }
 120
 121 void SmallStrings::createSingleCharacterString(JSGlobalData* globalData, unsigned char character)
 122 {
 123     if (!m_storage)
 124         m_storage.set(new SmallStringsStorage);
 125     ASSERT(!m_singleCharacterStrings[character]);
 126     m_singleCharacterStrings[character] = new (globalData) JSString(globalData, m_storage->rep(character), JSString::HasOtherOwner);
 127 }
 128
 129 UString::Rep* SmallStrings::singleCharacterStringRep(unsigned char character)
 130 {
 131     if (!m_storage)
 132         m_storage.set(new SmallStringsStorage);
 133     return m_storage->rep(character);
 134 }
 135
 136 } // namespace JSC