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<div class="title">bit_reader.cc</div> </div>
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<div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> <span class="comment">// Copyright (c) 2012 The Chromium Authors. All rights reserved.</span></div>
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<div class="line"><a name="l00002"></a><span class="lineno"> 2</span> <span class="comment">// Use of this source code is governed by a BSD-style license that can be</span></div>
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<div class="line"><a name="l00003"></a><span class="lineno"> 3</span> <span class="comment">// found in the LICENSE file.</span></div>
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<div class="line"><a name="l00004"></a><span class="lineno"> 4</span> </div>
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<div class="line"><a name="l00005"></a><span class="lineno"> 5</span> <span class="preprocessor">#include "packager/media/base/bit_reader.h"</span></div>
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<div class="line"><a name="l00006"></a><span class="lineno"> 6</span> </div>
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<div class="line"><a name="l00007"></a><span class="lineno"> 7</span> <span class="preprocessor">#include <algorithm></span></div>
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<div class="line"><a name="l00008"></a><span class="lineno"> 8</span> </div>
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<div class="line"><a name="l00009"></a><span class="lineno"> 9</span> <span class="keyword">namespace </span>edash_packager {</div>
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<div class="line"><a name="l00010"></a><span class="lineno"> 10</span> <span class="keyword">namespace </span>media {</div>
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<div class="line"><a name="l00011"></a><span class="lineno"> 11</span> </div>
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<div class="line"><a name="l00012"></a><span class="lineno"><a class="line" href="../../df/db4/classedash__packager_1_1media_1_1BitReader.html#a7cfecfaf6169a0c9286d62b24e7b934e"> 12</a></span> <a class="code" href="../../df/db4/classedash__packager_1_1media_1_1BitReader.html#a7cfecfaf6169a0c9286d62b24e7b934e">BitReader::BitReader</a>(<span class="keyword">const</span> uint8_t* data, off_t size)</div>
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<div class="line"><a name="l00013"></a><span class="lineno"> 13</span>  : data_(data), bytes_left_(size), num_remaining_bits_in_curr_byte_(0) {</div>
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<div class="line"><a name="l00014"></a><span class="lineno"> 14</span>  DCHECK(data_ != NULL && bytes_left_ > 0);</div>
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<div class="line"><a name="l00015"></a><span class="lineno"> 15</span> </div>
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<div class="line"><a name="l00016"></a><span class="lineno"> 16</span>  UpdateCurrByte();</div>
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<div class="line"><a name="l00017"></a><span class="lineno"> 17</span> }</div>
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<div class="line"><a name="l00018"></a><span class="lineno"> 18</span> </div>
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<div class="line"><a name="l00019"></a><span class="lineno"> 19</span> BitReader::~BitReader() {}</div>
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<div class="line"><a name="l00020"></a><span class="lineno"> 20</span> </div>
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<div class="line"><a name="l00021"></a><span class="lineno"><a class="line" href="../../df/db4/classedash__packager_1_1media_1_1BitReader.html#acacb97d71aaae01796b90d27e7cdca0a"> 21</a></span> <span class="keywordtype">bool</span> <a class="code" href="../../df/db4/classedash__packager_1_1media_1_1BitReader.html#acacb97d71aaae01796b90d27e7cdca0a">BitReader::SkipBits</a>(<span class="keywordtype">int</span> num_bits) {</div>
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<div class="line"><a name="l00022"></a><span class="lineno"> 22</span>  DCHECK_GE(num_bits, 0);</div>
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<div class="line"><a name="l00023"></a><span class="lineno"> 23</span> </div>
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<div class="line"><a name="l00024"></a><span class="lineno"> 24</span>  <span class="comment">// Skip any bits in the current byte waiting to be processed, then</span></div>
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<div class="line"><a name="l00025"></a><span class="lineno"> 25</span>  <span class="comment">// process full bytes until less than 8 bits remaining.</span></div>
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<div class="line"><a name="l00026"></a><span class="lineno"> 26</span>  <span class="keywordflow">if</span> (num_bits > num_remaining_bits_in_curr_byte_) {</div>
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<div class="line"><a name="l00027"></a><span class="lineno"> 27</span>  num_bits -= num_remaining_bits_in_curr_byte_;</div>
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<div class="line"><a name="l00028"></a><span class="lineno"> 28</span>  num_remaining_bits_in_curr_byte_ = 0;</div>
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<div class="line"><a name="l00029"></a><span class="lineno"> 29</span> </div>
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<div class="line"><a name="l00030"></a><span class="lineno"> 30</span>  <span class="keywordtype">int</span> num_bytes = num_bits / 8;</div>
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<div class="line"><a name="l00031"></a><span class="lineno"> 31</span>  num_bits %= 8;</div>
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<div class="line"><a name="l00032"></a><span class="lineno"> 32</span>  <span class="keywordflow">if</span> (bytes_left_ < num_bytes) {</div>
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<div class="line"><a name="l00033"></a><span class="lineno"> 33</span>  bytes_left_ = 0;</div>
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<div class="line"><a name="l00034"></a><span class="lineno"> 34</span>  <span class="keywordflow">return</span> <span class="keyword">false</span>;</div>
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<div class="line"><a name="l00035"></a><span class="lineno"> 35</span>  }</div>
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<div class="line"><a name="l00036"></a><span class="lineno"> 36</span>  bytes_left_ -= num_bytes;</div>
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<div class="line"><a name="l00037"></a><span class="lineno"> 37</span>  data_ += num_bytes;</div>
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<div class="line"><a name="l00038"></a><span class="lineno"> 38</span>  UpdateCurrByte();</div>
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<div class="line"><a name="l00039"></a><span class="lineno"> 39</span> </div>
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<div class="line"><a name="l00040"></a><span class="lineno"> 40</span>  <span class="comment">// If there is no more data remaining, only return true if we</span></div>
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<div class="line"><a name="l00041"></a><span class="lineno"> 41</span>  <span class="comment">// skipped all that were requested.</span></div>
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<div class="line"><a name="l00042"></a><span class="lineno"> 42</span>  <span class="keywordflow">if</span> (num_remaining_bits_in_curr_byte_ == 0)</div>
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<div class="line"><a name="l00043"></a><span class="lineno"> 43</span>  <span class="keywordflow">return</span> (num_bits == 0);</div>
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<div class="line"><a name="l00044"></a><span class="lineno"> 44</span>  }</div>
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<div class="line"><a name="l00045"></a><span class="lineno"> 45</span> </div>
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<div class="line"><a name="l00046"></a><span class="lineno"> 46</span>  <span class="comment">// Less than 8 bits remaining to skip. Use ReadBitsInternal to verify</span></div>
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<div class="line"><a name="l00047"></a><span class="lineno"> 47</span>  <span class="comment">// that the remaining bits we need exist, and adjust them as necessary</span></div>
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<div class="line"><a name="l00048"></a><span class="lineno"> 48</span>  <span class="comment">// for subsequent operations.</span></div>
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<div class="line"><a name="l00049"></a><span class="lineno"> 49</span>  uint64_t not_needed;</div>
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<div class="line"><a name="l00050"></a><span class="lineno"> 50</span>  <span class="keywordflow">return</span> ReadBitsInternal(num_bits, &not_needed);</div>
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<div class="line"><a name="l00051"></a><span class="lineno"> 51</span> }</div>
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<div class="line"><a name="l00052"></a><span class="lineno"> 52</span> </div>
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<div class="line"><a name="l00053"></a><span class="lineno"><a class="line" href="../../df/db4/classedash__packager_1_1media_1_1BitReader.html#a1409a0968749ca5a55ba823cd718065b"> 53</a></span> <span class="keywordtype">int</span> <a class="code" href="../../df/db4/classedash__packager_1_1media_1_1BitReader.html#a1409a0968749ca5a55ba823cd718065b">BitReader::bits_available</a>()<span class="keyword"> const </span>{</div>
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<div class="line"><a name="l00054"></a><span class="lineno"> 54</span>  <span class="keywordflow">return</span> 8 * bytes_left_ + num_remaining_bits_in_curr_byte_;</div>
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<div class="line"><a name="l00055"></a><span class="lineno"> 55</span> }</div>
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<div class="line"><a name="l00056"></a><span class="lineno"> 56</span> </div>
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<div class="line"><a name="l00057"></a><span class="lineno"> 57</span> <span class="keywordtype">bool</span> BitReader::ReadBitsInternal(<span class="keywordtype">int</span> num_bits, uint64_t* out) {</div>
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<div class="line"><a name="l00058"></a><span class="lineno"> 58</span>  DCHECK_LE(num_bits, 64);</div>
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<div class="line"><a name="l00059"></a><span class="lineno"> 59</span> </div>
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<div class="line"><a name="l00060"></a><span class="lineno"> 60</span>  *out = 0;</div>
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<div class="line"><a name="l00061"></a><span class="lineno"> 61</span> </div>
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<div class="line"><a name="l00062"></a><span class="lineno"> 62</span>  <span class="keywordflow">while</span> (num_remaining_bits_in_curr_byte_ != 0 && num_bits != 0) {</div>
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<div class="line"><a name="l00063"></a><span class="lineno"> 63</span>  <span class="keywordtype">int</span> bits_to_take = std::min(num_remaining_bits_in_curr_byte_, num_bits);</div>
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<div class="line"><a name="l00064"></a><span class="lineno"> 64</span> </div>
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<div class="line"><a name="l00065"></a><span class="lineno"> 65</span>  *out <<= bits_to_take;</div>
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<div class="line"><a name="l00066"></a><span class="lineno"> 66</span>  *out += curr_byte_ >> (num_remaining_bits_in_curr_byte_ - bits_to_take);</div>
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<div class="line"><a name="l00067"></a><span class="lineno"> 67</span>  num_bits -= bits_to_take;</div>
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<div class="line"><a name="l00068"></a><span class="lineno"> 68</span>  num_remaining_bits_in_curr_byte_ -= bits_to_take;</div>
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<div class="line"><a name="l00069"></a><span class="lineno"> 69</span>  curr_byte_ &= (1 << num_remaining_bits_in_curr_byte_) - 1;</div>
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<div class="line"><a name="l00070"></a><span class="lineno"> 70</span> </div>
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<div class="line"><a name="l00071"></a><span class="lineno"> 71</span>  <span class="keywordflow">if</span> (num_remaining_bits_in_curr_byte_ == 0)</div>
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<div class="line"><a name="l00072"></a><span class="lineno"> 72</span>  UpdateCurrByte();</div>
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<div class="line"><a name="l00073"></a><span class="lineno"> 73</span>  }</div>
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<div class="line"><a name="l00074"></a><span class="lineno"> 74</span> </div>
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<div class="line"><a name="l00075"></a><span class="lineno"> 75</span>  <span class="keywordflow">return</span> num_bits == 0;</div>
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<div class="line"><a name="l00076"></a><span class="lineno"> 76</span> }</div>
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<div class="line"><a name="l00077"></a><span class="lineno"> 77</span> </div>
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<div class="line"><a name="l00078"></a><span class="lineno"> 78</span> <span class="keywordtype">void</span> BitReader::UpdateCurrByte() {</div>
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<div class="line"><a name="l00079"></a><span class="lineno"> 79</span>  DCHECK_EQ(num_remaining_bits_in_curr_byte_, 0);</div>
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<div class="line"><a name="l00080"></a><span class="lineno"> 80</span> </div>
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<div class="line"><a name="l00081"></a><span class="lineno"> 81</span>  <span class="keywordflow">if</span> (bytes_left_ == 0)</div>
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<div class="line"><a name="l00082"></a><span class="lineno"> 82</span>  <span class="keywordflow">return</span>;</div>
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<div class="line"><a name="l00083"></a><span class="lineno"> 83</span> </div>
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<div class="line"><a name="l00084"></a><span class="lineno"> 84</span>  <span class="comment">// Load a new byte and advance pointers.</span></div>
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<div class="line"><a name="l00085"></a><span class="lineno"> 85</span>  curr_byte_ = *data_;</div>
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<div class="line"><a name="l00086"></a><span class="lineno"> 86</span>  ++data_;</div>
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<div class="line"><a name="l00087"></a><span class="lineno"> 87</span>  --bytes_left_;</div>
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<div class="line"><a name="l00088"></a><span class="lineno"> 88</span>  num_remaining_bits_in_curr_byte_ = 8;</div>
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<div class="line"><a name="l00089"></a><span class="lineno"> 89</span> }</div>
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<div class="line"><a name="l00090"></a><span class="lineno"> 90</span> </div>
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<div class="line"><a name="l00091"></a><span class="lineno"> 91</span> } <span class="comment">// namespace media</span></div>
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<div class="line"><a name="l00092"></a><span class="lineno"> 92</span> } <span class="comment">// namespace edash_packager</span></div>
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<div class="ttc" id="classedash__packager_1_1media_1_1BitReader_html_a7cfecfaf6169a0c9286d62b24e7b934e"><div class="ttname"><a href="../../df/db4/classedash__packager_1_1media_1_1BitReader.html#a7cfecfaf6169a0c9286d62b24e7b934e">edash_packager::media::BitReader::BitReader</a></div><div class="ttdeci">BitReader(const uint8_t *data, off_t size)</div><div class="ttdef"><b>Definition:</b> <a href="../../d5/de0/bit__reader_8cc_source.html#l00012">bit_reader.cc:12</a></div></div>
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<div class="ttc" id="classedash__packager_1_1media_1_1BitReader_html_a1409a0968749ca5a55ba823cd718065b"><div class="ttname"><a href="../../df/db4/classedash__packager_1_1media_1_1BitReader.html#a1409a0968749ca5a55ba823cd718065b">edash_packager::media::BitReader::bits_available</a></div><div class="ttdeci">int bits_available() const </div><div class="ttdef"><b>Definition:</b> <a href="../../d5/de0/bit__reader_8cc_source.html#l00053">bit_reader.cc:53</a></div></div>
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<div class="ttc" id="classedash__packager_1_1media_1_1BitReader_html_acacb97d71aaae01796b90d27e7cdca0a"><div class="ttname"><a href="../../df/db4/classedash__packager_1_1media_1_1BitReader.html#acacb97d71aaae01796b90d27e7cdca0a">edash_packager::media::BitReader::SkipBits</a></div><div class="ttdeci">bool SkipBits(int num_bits)</div><div class="ttdef"><b>Definition:</b> <a href="../../d5/de0/bit__reader_8cc_source.html#l00021">bit_reader.cc:21</a></div></div>
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