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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"><title>audio/G711.cpp Source File</title><link href="doxygen.css" rel="stylesheet" type="text/css"></head><body><!-- Generated by Doxygen 1.4.4 --><div class="qindex"><a class="qindex" href="index.html">Main Page</a> | <a class="qindex" href="modules.html">Modules</a> | <a class="qindex" href="hierarchy.html">Class Hierarchy</a> | <a class="qindex" href="annotated.html">Class List</a> | <a class="qindex" href="dirs.html">Directories</a> | <a class="qindex" href="files.html">File List</a> | <a class="qindex" href="functions.html">Class Members</a> | <a class="qindex" href="globals.html">File Members</a></div><div class="nav"><a class="el" href="dir_000000.html">audio</a></div><h1>G711.cpp</h1><a href="G711_8cpp.html">Go to the documentation of this file.</a><div class="fragment"><pre class="fragment"><a name="l00001"></a>00001 <a name="l00025"></a>00025 <span class="preprocessor">#include "<a class="code" href="common_8h.html">common.h</a>"</span><a name="l00026"></a>00026 <span class="preprocessor">#include "<a class="code" href="G711_8h.html">G711.h</a>"</span><a name="l00027"></a>00027 <a name="l00028"></a>00028 <a name="l00029"></a>00029 <span class="comment">/*</span><a name="l00030"></a>00030 <span class="comment">Members of class G711</span><a name="l00031"></a>00031 <span class="comment">*/</span><a name="l00032"></a>00032 <a name="l00033"></a>00033 <a name="l00034"></a><a class="code" href="classG711.html#e0">00034</a> <a class="code" href="common_8h.html#a2">EXPORT</a> <a class="code" href="group__integers.html#ga0">uint8</a> <a class="code" href="classG711.html#e0">G711::ALawEncode</a>(<a class="code" href="group__integers.html#ga4">int16</a> pcm16)<a name="l00035"></a>00035 {<a name="l00036"></a>00036 <span class="keywordtype">int</span> p = pcm16;<a name="l00037"></a>00037 <a class="code" href="group__integers.html#ga6">uint</a> a; <span class="comment">// A-law value we are forming</span><a name="l00038"></a>00038 <span class="keywordflow">if</span>(p<0)<a name="l00039"></a>00039 {<a name="l00040"></a>00040 <span class="comment">// -ve value</span><a name="l00041"></a>00041 <span class="comment">// Note, ones compliment is used here as this keeps encoding symetrical</span><a name="l00042"></a>00042 <span class="comment">// and equal spaced around zero cross-over, (it also matches the standard).</span><a name="l00043"></a>00043 p = ~p;<a name="l00044"></a>00044 a = 0x00; <span class="comment">// sign = 0</span><a name="l00045"></a>00045 }<a name="l00046"></a>00046 <span class="keywordflow">else</span><a name="l00047"></a>00047 {<a name="l00048"></a>00048 <span class="comment">// +ve value</span><a name="l00049"></a>00049 a = 0x80; <span class="comment">// sign = 1</span><a name="l00050"></a>00050 }<a name="l00051"></a>00051 <a name="l00052"></a>00052 <span class="comment">// Calculate segment and interval numbers</span><a name="l00053"></a>00053 p >>= 4;<a name="l00054"></a>00054 <span class="keywordflow">if</span>(p>=0x20)<a name="l00055"></a>00055 {<a name="l00056"></a>00056 <span class="keywordflow">if</span>(p>=0x100)<a name="l00057"></a>00057 {<a name="l00058"></a>00058 p >>= 4;<a name="l00059"></a>00059 a += 0x40;<a name="l00060"></a>00060 }<a name="l00061"></a>00061 <span class="keywordflow">if</span>(p>=0x40)<a name="l00062"></a>00062 {<a name="l00063"></a>00063 p >>= 2;<a name="l00064"></a>00064 a += 0x20;<a name="l00065"></a>00065 }<a name="l00066"></a>00066 <span class="keywordflow">if</span>(p>=0x20)<a name="l00067"></a>00067 {<a name="l00068"></a>00068 p >>= 1;<a name="l00069"></a>00069 a += 0x10;<a name="l00070"></a>00070 }<a name="l00071"></a>00071 }<a name="l00072"></a>00072 <span class="comment">// a&0x70 now holds segment value and 'p' the interval number</span><a name="l00073"></a>00073 <a name="l00074"></a>00074 a += p; <span class="comment">// a now equal to encoded A-law value</span><a name="l00075"></a>00075 <a name="l00076"></a>00076 <span class="keywordflow">return</span> a^0x55; <span class="comment">// A-law has alternate bits inverted for transmission</span><a name="l00077"></a>00077 }<a name="l00078"></a>00078 <a name="l00079"></a>00079 <a name="l00080"></a><a class="code" href="classG711.html#e1">00080</a> <a class="code" href="common_8h.html#a2">EXPORT</a> <span class="keywordtype">int</span> <a class="code" href="classG711.html#e1">G711::ALawDecode</a>(<a class="code" href="group__integers.html#ga0">uint8</a> alaw)<a name="l00081"></a>00081 {<a name="l00082"></a>00082 alaw ^= 0x55; <span class="comment">// A-law has alternate bits inverted for transmission</span><a name="l00083"></a>00083 <a name="l00084"></a>00084 <a class="code" href="group__integers.html#ga6">uint</a> sign = alaw&0x80;<a name="l00085"></a>00085 <a name="l00086"></a>00086 <span class="keywordtype">int</span> linear = alaw&0x1f;<a name="l00087"></a>00087 linear <<= 4;<a name="l00088"></a>00088 linear += 8; <span class="comment">// Add a 'half' bit (0x08) to place PCM value in middle of range</span><a name="l00089"></a>00089 <a name="l00090"></a>00090 alaw &= 0x7f;<a name="l00091"></a>00091 <span class="keywordflow">if</span>(alaw>=0x20)<a name="l00092"></a>00092 {<a name="l00093"></a>00093 linear |= 0x100; <span class="comment">// Put in MSB</span><a name="l00094"></a>00094 <a class="code" href="group__integers.html#ga6">uint</a> shift = (alaw>>4)-1;<a name="l00095"></a>00095 linear <<= shift;<a name="l00096"></a>00096 }<a name="l00097"></a>00097 <a name="l00098"></a>00098 <span class="keywordflow">if</span>(!sign)<a name="l00099"></a>00099 <span class="keywordflow">return</span> -linear;<a name="l00100"></a>00100 <span class="keywordflow">else</span><a name="l00101"></a>00101 <span class="keywordflow">return</span> linear;<a name="l00102"></a>00102 }<a name="l00103"></a>00103 <a name="l00104"></a>00104 <a name="l00105"></a><a class="code" href="classG711.html#e2">00105</a> <a class="code" href="common_8h.html#a2">EXPORT</a> <a class="code" href="group__integers.html#ga0">uint8</a> <a class="code" href="classG711.html#e2">G711::ULawEncode</a>(<a class="code" href="group__integers.html#ga4">int16</a> pcm16)<a name="l00106"></a>00106 {<a name="l00107"></a>00107 <span class="keywordtype">int</span> p = pcm16;<a name="l00108"></a>00108 <a class="code" href="group__integers.html#ga6">uint</a> u; <span class="comment">// u-law value we are forming</span><a name="l00109"></a>00109 <a name="l00110"></a>00110 <span class="keywordflow">if</span>(p<0)<a name="l00111"></a>00111 {<a name="l00112"></a>00112 <span class="comment">// -ve value</span><a name="l00113"></a>00113 <span class="comment">// Note, ones compliment is used here as this keeps encoding symetrical</span><a name="l00114"></a>00114 <span class="comment">// and equal spaced around zero cross-over, (it also matches the standard).</span><a name="l00115"></a>00115 p = ~p;<a name="l00116"></a>00116 u = 0x80^0x10^0xff; <span class="comment">// Sign bit = 1 (^0x10 because this will get inverted later) ^0xff to invert final u-Law code</span><a name="l00117"></a>00117 }<a name="l00118"></a>00118 <span class="keywordflow">else</span><a name="l00119"></a>00119 {<a name="l00120"></a>00120 <span class="comment">// +ve value</span><a name="l00121"></a>00121 u = 0x00^0x10^0xff; <span class="comment">// Sign bit = 0 (-0x10 because this amount extra will get added later) ^0xff to invert final u-Law code</span><a name="l00122"></a>00122 }<a name="l00123"></a>00123 <a name="l00124"></a>00124 p += 0x84; <span class="comment">// Add uLaw bias</span><a name="l00125"></a>00125 <a name="l00126"></a>00126 <span class="keywordflow">if</span>(p>0x7f00)<a name="l00127"></a>00127 p = 0x7f00; <span class="comment">// Clip to 15 bits</span><a name="l00128"></a>00128 <a name="l00129"></a>00129 <span class="comment">// Calculate segment and interval numbers</span><a name="l00130"></a>00130 p >>= 3; <span class="comment">// Shift down to 13bit</span><a name="l00131"></a>00131 <span class="keywordflow">if</span>(p>=0x100)<a name="l00132"></a>00132 {<a name="l00133"></a>00133 p >>= 4;<a name="l00134"></a>00134 u ^= 0x40;<a name="l00135"></a>00135 }<a name="l00136"></a>00136 <span class="keywordflow">if</span>(p>=0x40)<a name="l00137"></a>00137 {<a name="l00138"></a>00138 p >>= 2;<a name="l00139"></a>00139 u ^= 0x20;<a name="l00140"></a>00140 }<a name="l00141"></a>00141 <span class="keywordflow">if</span>(p>=0x20)<a name="l00142"></a>00142 {<a name="l00143"></a>00143 p >>= 1;<a name="l00144"></a>00144 u ^= 0x10;<a name="l00145"></a>00145 }<a name="l00146"></a>00146 <span class="comment">// (u^0x10)&0x70 now equal to the segment value and 'p' the interval number (^0x10)</span><a name="l00147"></a>00147 <a name="l00148"></a>00148 u ^= p; <span class="comment">// u now equal to encoded u-law value (with all bits inverted)</span><a name="l00149"></a>00149 <a name="l00150"></a>00150 <span class="keywordflow">return</span> u;⌨️ 快捷键说明
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