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      1 /*
      2  * Copyright (C) 2013 Google 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 are
      6  * met:
      7  *
      8  *     * Redistributions of source code must retain the above copyright
      9  * notice, this list of conditions and the following disclaimer.
     10  *     * Redistributions in binary form must reproduce the above
     11  * copyright notice, this list of conditions and the following disclaimer
     12  * in the documentation and/or other materials provided with the
     13  * distribution.
     14  *     * Neither the name of Google Inc. nor the names of its
     15  * contributors may be used to endorse or promote products derived from
     16  * this software without specific prior written permission.
     17  *
     18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     19  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     21  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     22  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     23  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
     24  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     28  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     29  */
     30 
     31 #include "config.h"
     32 #include "wtf/ArrayBufferBuilder.h"
     33 
     34 #include "wtf/Assertions.h"
     35 #include <limits>
     36 
     37 namespace WTF {
     38 
     39 static const int defaultBufferCapacity = 32768;
     40 
     41 ArrayBufferBuilder::ArrayBufferBuilder()
     42     : m_bytesUsed(0)
     43     , m_variableCapacity(true)
     44 {
     45     m_buffer = ArrayBuffer::create(defaultBufferCapacity, 1);
     46 }
     47 
     48 bool ArrayBufferBuilder::expandCapacity(unsigned sizeToIncrease)
     49 {
     50     unsigned currentBufferSize = m_buffer->byteLength();
     51 
     52     // If the size of the buffer exceeds max of unsigned, it can't be grown any
     53     // more.
     54     if (sizeToIncrease > std::numeric_limits<unsigned>::max() - m_bytesUsed)
     55         return false;
     56 
     57     unsigned newBufferSize = m_bytesUsed + sizeToIncrease;
     58 
     59     // Grow exponentially if possible.
     60     unsigned exponentialGrowthNewBufferSize = std::numeric_limits<unsigned>::max();
     61     if (currentBufferSize <= std::numeric_limits<unsigned>::max() / 2)
     62         exponentialGrowthNewBufferSize = currentBufferSize * 2;
     63     if (exponentialGrowthNewBufferSize > newBufferSize)
     64         newBufferSize = exponentialGrowthNewBufferSize;
     65 
     66     // Copy existing data in current buffer to new buffer.
     67     RefPtr<ArrayBuffer> newBuffer = ArrayBuffer::create(newBufferSize, 1);
     68     if (!newBuffer)
     69         return false;
     70 
     71     memcpy(newBuffer->data(), m_buffer->data(), m_bytesUsed);
     72     m_buffer = newBuffer;
     73     return true;
     74 }
     75 
     76 unsigned ArrayBufferBuilder::append(const char* data, unsigned length)
     77 {
     78     ASSERT(length > 0);
     79 
     80     unsigned currentBufferSize = m_buffer->byteLength();
     81 
     82     ASSERT(m_bytesUsed <= currentBufferSize);
     83 
     84     unsigned remainingBufferSpace = currentBufferSize - m_bytesUsed;
     85 
     86     unsigned bytesToSave = length;
     87 
     88     if (length > remainingBufferSpace) {
     89         if (m_variableCapacity) {
     90             if (!expandCapacity(length))
     91                 return 0;
     92         } else {
     93             bytesToSave = remainingBufferSpace;
     94         }
     95     }
     96 
     97     memcpy(static_cast<char*>(m_buffer->data()) + m_bytesUsed, data, bytesToSave);
     98     m_bytesUsed += bytesToSave;
     99 
    100     return bytesToSave;
    101 }
    102 
    103 PassRefPtr<ArrayBuffer> ArrayBufferBuilder::toArrayBuffer()
    104 {
    105     // Fully used. Return m_buffer as-is.
    106     if (m_buffer->byteLength() == m_bytesUsed)
    107         return m_buffer;
    108 
    109     return m_buffer->slice(0, m_bytesUsed);
    110 }
    111 
    112 String ArrayBufferBuilder::toString()
    113 {
    114     return String(static_cast<const char*>(m_buffer->data()), m_bytesUsed);
    115 }
    116 
    117 void ArrayBufferBuilder::shrinkToFit()
    118 {
    119     ASSERT(m_bytesUsed <= m_buffer->byteLength());
    120 
    121     if (m_buffer->byteLength() > m_bytesUsed)
    122         m_buffer = m_buffer->slice(0, m_bytesUsed);
    123 }
    124 
    125 } // namespace WTF
    126