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<a href="iir__filter_8h.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> <span class="comment">/* -*- c++ -*- */</span></div>
<div class="line"><a name="l00002"></a><span class="lineno"> 2</span> <span class="comment">/*</span></div>
<div class="line"><a name="l00003"></a><span class="lineno"> 3</span> <span class="comment"> * Copyright 2002,2012 Free Software Foundation, Inc.</span></div>
<div class="line"><a name="l00004"></a><span class="lineno"> 4</span> <span class="comment"> *</span></div>
<div class="line"><a name="l00005"></a><span class="lineno"> 5</span> <span class="comment"> * This file is part of GNU Radio</span></div>
<div class="line"><a name="l00006"></a><span class="lineno"> 6</span> <span class="comment"> *</span></div>
<div class="line"><a name="l00007"></a><span class="lineno"> 7</span> <span class="comment"> * GNU Radio is free software; you can redistribute it and/or modify</span></div>
<div class="line"><a name="l00008"></a><span class="lineno"> 8</span> <span class="comment"> * it under the terms of the GNU General Public License as published by</span></div>
<div class="line"><a name="l00009"></a><span class="lineno"> 9</span> <span class="comment"> * the Free Software Foundation; either version 3, or (at your option)</span></div>
<div class="line"><a name="l00010"></a><span class="lineno"> 10</span> <span class="comment"> * any later version.</span></div>
<div class="line"><a name="l00011"></a><span class="lineno"> 11</span> <span class="comment"> *</span></div>
<div class="line"><a name="l00012"></a><span class="lineno"> 12</span> <span class="comment"> * GNU Radio is distributed in the hope that it will be useful,</span></div>
<div class="line"><a name="l00013"></a><span class="lineno"> 13</span> <span class="comment"> * but WITHOUT ANY WARRANTY; without even the implied warranty of</span></div>
<div class="line"><a name="l00014"></a><span class="lineno"> 14</span> <span class="comment"> * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the</span></div>
<div class="line"><a name="l00015"></a><span class="lineno"> 15</span> <span class="comment"> * GNU General Public License for more details.</span></div>
<div class="line"><a name="l00016"></a><span class="lineno"> 16</span> <span class="comment"> *</span></div>
<div class="line"><a name="l00017"></a><span class="lineno"> 17</span> <span class="comment"> * You should have received a copy of the GNU General Public License</span></div>
<div class="line"><a name="l00018"></a><span class="lineno"> 18</span> <span class="comment"> * along with GNU Radio; see the file COPYING. If not, write to</span></div>
<div class="line"><a name="l00019"></a><span class="lineno"> 19</span> <span class="comment"> * the Free Software Foundation, Inc., 51 Franklin Street,</span></div>
<div class="line"><a name="l00020"></a><span class="lineno"> 20</span> <span class="comment"> * Boston, MA 02110-1301, USA.</span></div>
<div class="line"><a name="l00021"></a><span class="lineno"> 21</span> <span class="comment"> */</span></div>
<div class="line"><a name="l00022"></a><span class="lineno"> 22</span> </div>
<div class="line"><a name="l00023"></a><span class="lineno"> 23</span> <span class="preprocessor">#ifndef INCLUDED_IIR_FILTER_H</span></div>
<div class="line"><a name="l00024"></a><span class="lineno"> 24</span> <span class="preprocessor"></span><span class="preprocessor">#define INCLUDED_IIR_FILTER_H</span></div>
<div class="line"><a name="l00025"></a><span class="lineno"> 25</span> <span class="preprocessor"></span></div>
<div class="line"><a name="l00026"></a><span class="lineno"> 26</span> <span class="preprocessor">#include <<a class="code" href="gr-filter_2include_2filter_2api_8h.html">filter/api.h</a>></span></div>
<div class="line"><a name="l00027"></a><span class="lineno"> 27</span> <span class="preprocessor">#include <vector></span></div>
<div class="line"><a name="l00028"></a><span class="lineno"> 28</span> <span class="preprocessor">#include <stdexcept></span></div>
<div class="line"><a name="l00029"></a><span class="lineno"> 29</span> </div>
<div class="line"><a name="l00030"></a><span class="lineno"> 30</span> <span class="keyword">namespace </span>gr {</div>
<div class="line"><a name="l00031"></a><span class="lineno"> 31</span>  <span class="keyword">namespace </span>filter {</div>
<div class="line"><a name="l00032"></a><span class="lineno"> 32</span>  <span class="keyword">namespace </span>kernel {</div>
<div class="line"><a name="l00033"></a><span class="lineno"> 33</span> <span class="comment"></span></div>
<div class="line"><a name="l00034"></a><span class="lineno"> 34</span> <span class="comment"> /*!</span></div>
<div class="line"><a name="l00035"></a><span class="lineno"> 35</span> <span class="comment"> * \brief base class template for Infinite Impulse Response filter (IIR)</span></div>
<div class="line"><a name="l00036"></a><span class="lineno"> 36</span> <span class="comment"> */</span></div>
<div class="line"><a name="l00037"></a><span class="lineno"> 37</span>  <span class="keyword">template</span><<span class="keyword">class</span> i_type, <span class="keyword">class</span> o_type, <span class="keyword">class</span> tap_type></div>
<div class="line"><a name="l00038"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html"> 38</a></span>  <span class="keyword">class </span><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html" title="base class template for Infinite Impulse Response filter (IIR)">iir_filter</a></div>
<div class="line"><a name="l00039"></a><span class="lineno"> 39</span>  {</div>
<div class="line"><a name="l00040"></a><span class="lineno"> 40</span>  <span class="keyword">public</span>:<span class="comment"></span></div>
<div class="line"><a name="l00041"></a><span class="lineno"> 41</span> <span class="comment"> /*!</span></div>
<div class="line"><a name="l00042"></a><span class="lineno"> 42</span> <span class="comment"> * \brief Construct an IIR with the given taps.</span></div>
<div class="line"><a name="l00043"></a><span class="lineno"> 43</span> <span class="comment"> *</span></div>
<div class="line"><a name="l00044"></a><span class="lineno"> 44</span> <span class="comment"> * This filter uses the Direct Form I implementation, where</span></div>
<div class="line"><a name="l00045"></a><span class="lineno"> 45</span> <span class="comment"> * \p fftaps contains the feed-forward taps, and \p fbtaps the feedback ones.</span></div>
<div class="line"><a name="l00046"></a><span class="lineno"> 46</span> <span class="comment"> *</span></div>
<div class="line"><a name="l00047"></a><span class="lineno"> 47</span> <span class="comment"> * \p fftaps and \p fbtaps must have equal numbers of taps</span></div>
<div class="line"><a name="l00048"></a><span class="lineno"> 48</span> <span class="comment"> *</span></div>
<div class="line"><a name="l00049"></a><span class="lineno"> 49</span> <span class="comment"> * The input and output satisfy a difference equation of the form</span></div>
<div class="line"><a name="l00050"></a><span class="lineno"> 50</span> <span class="comment"></span></div>
<div class="line"><a name="l00051"></a><span class="lineno"> 51</span> <span class="comment"> \f[</span></div>
<div class="line"><a name="l00052"></a><span class="lineno"> 52</span> <span class="comment"> y[n] - \sum_{k=1}^{M} a_k y[n-k] = \sum_{k=0}^{N} b_k x[n-k]</span></div>
<div class="line"><a name="l00053"></a><span class="lineno"> 53</span> <span class="comment"> \f]</span></div>
<div class="line"><a name="l00054"></a><span class="lineno"> 54</span> <span class="comment"></span></div>
<div class="line"><a name="l00055"></a><span class="lineno"> 55</span> <span class="comment"> * with the corresponding rational system function</span></div>
<div class="line"><a name="l00056"></a><span class="lineno"> 56</span> <span class="comment"></span></div>
<div class="line"><a name="l00057"></a><span class="lineno"> 57</span> <span class="comment"> \f[</span></div>
<div class="line"><a name="l00058"></a><span class="lineno"> 58</span> <span class="comment"> H(z) = \frac{\sum_{k=0}^{N} b_k z^{-k}}{1 - \sum_{k=1}^{M} a_k z^{-k}}</span></div>
<div class="line"><a name="l00059"></a><span class="lineno"> 59</span> <span class="comment"> \f]</span></div>
<div class="line"><a name="l00060"></a><span class="lineno"> 60</span> <span class="comment"></span></div>
<div class="line"><a name="l00061"></a><span class="lineno"> 61</span> <span class="comment"> * Note that some texts define the system function with a + in</span></div>
<div class="line"><a name="l00062"></a><span class="lineno"> 62</span> <span class="comment"> * the denominator. If you're using that convention, you'll</span></div>
<div class="line"><a name="l00063"></a><span class="lineno"> 63</span> <span class="comment"> * need to negate the feedback taps.</span></div>
<div class="line"><a name="l00064"></a><span class="lineno"> 64</span> <span class="comment"> */</span></div>
<div class="line"><a name="l00065"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#abb4c0147e6f7ca94b0766b48f31858c5"> 65</a></span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a414bb007d2da38867e9e4e6da0f66def">iir_filter</a>(<span class="keyword">const</span> std::vector<tap_type>& fftaps,</div>
<div class="line"><a name="l00066"></a><span class="lineno"> 66</span>  <span class="keyword">const</span> std::vector<tap_type>& fbtaps) <span class="keywordflow">throw</span> (std::invalid_argument)</div>
<div class="line"><a name="l00067"></a><span class="lineno"> 67</span>  {</div>
<div class="line"><a name="l00068"></a><span class="lineno"> 68</span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a1ff87eaff39dcb007f79ed595f7cf7d3" title="install new taps.">set_taps</a>(fftaps, fbtaps);</div>
<div class="line"><a name="l00069"></a><span class="lineno"> 69</span>  }</div>
<div class="line"><a name="l00070"></a><span class="lineno"> 70</span> </div>
<div class="line"><a name="l00071"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a414bb007d2da38867e9e4e6da0f66def"> 71</a></span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a414bb007d2da38867e9e4e6da0f66def">iir_filter</a>() : <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a9871f95fae0caa9591c4a6efead64528">d_latest_n</a>(0),<a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a4363ff21e735805cba8d74331d6bed21">d_latest_m</a>(0) { }</div>
<div class="line"><a name="l00072"></a><span class="lineno"> 72</span> </div>
<div class="line"><a name="l00073"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#ae3c1ae8c68057c7fd4ab6082ef916daa"> 73</a></span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#ae3c1ae8c68057c7fd4ab6082ef916daa">~iir_filter</a>() {}</div>
<div class="line"><a name="l00074"></a><span class="lineno"> 74</span> <span class="comment"></span></div>
<div class="line"><a name="l00075"></a><span class="lineno"> 75</span> <span class="comment"> /*!</span></div>
<div class="line"><a name="l00076"></a><span class="lineno"> 76</span> <span class="comment"> * \brief compute a single output value.</span></div>
<div class="line"><a name="l00077"></a><span class="lineno"> 77</span> <span class="comment"> * \returns the filtered input value.</span></div>
<div class="line"><a name="l00078"></a><span class="lineno"> 78</span> <span class="comment"> */</span></div>
<div class="line"><a name="l00079"></a><span class="lineno"> 79</span>  o_type <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a34b16ee180319b1398049e591fbd8d07" title="compute a single output value.">filter</a>(<span class="keyword">const</span> i_type input);</div>
<div class="line"><a name="l00080"></a><span class="lineno"> 80</span> <span class="comment"></span></div>
<div class="line"><a name="l00081"></a><span class="lineno"> 81</span> <span class="comment"> /*!</span></div>
<div class="line"><a name="l00082"></a><span class="lineno"> 82</span> <span class="comment"> * \brief compute an array of N output values.</span></div>
<div class="line"><a name="l00083"></a><span class="lineno"> 83</span> <span class="comment"> * \p input must have N valid entries.</span></div>
<div class="line"><a name="l00084"></a><span class="lineno"> 84</span> <span class="comment"> */</span></div>
<div class="line"><a name="l00085"></a><span class="lineno"> 85</span>  <span class="keywordtype">void</span> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a8549335490780d0d59f86908f2675d78" title="compute an array of N output values. input must have N valid entries.">filter_n</a>(o_type output[], <span class="keyword">const</span> i_type input[], <span class="keywordtype">long</span> n);</div>
<div class="line"><a name="l00086"></a><span class="lineno"> 86</span> <span class="comment"></span></div>
<div class="line"><a name="l00087"></a><span class="lineno"> 87</span> <span class="comment"> /*!</span></div>
<div class="line"><a name="l00088"></a><span class="lineno"> 88</span> <span class="comment"> * \return number of taps in filter.</span></div>
<div class="line"><a name="l00089"></a><span class="lineno"> 89</span> <span class="comment"> */</span></div>
<div class="line"><a name="l00090"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a32c5364bdb75267f521f9e187f8a1d82"> 90</a></span>  <span class="keywordtype">unsigned</span> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a32c5364bdb75267f521f9e187f8a1d82">ntaps_ff</a>()<span class="keyword"> const </span>{ <span class="keywordflow">return</span> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a903e4f9873bdd2946b8bc010dee0549f">d_fftaps</a>.size(); }</div>
<div class="line"><a name="l00091"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#ab61086d9741834074cf6732d86fd483f"> 91</a></span>  <span class="keywordtype">unsigned</span> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#ab61086d9741834074cf6732d86fd483f">ntaps_fb</a>()<span class="keyword"> const </span>{ <span class="keywordflow">return</span> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#adf311b2c19a1891e27a8e59d22f8cd54">d_fbtaps</a>.size(); }</div>
<div class="line"><a name="l00092"></a><span class="lineno"> 92</span> <span class="comment"></span></div>
<div class="line"><a name="l00093"></a><span class="lineno"> 93</span> <span class="comment"> /*!</span></div>
<div class="line"><a name="l00094"></a><span class="lineno"> 94</span> <span class="comment"> * \brief install new taps.</span></div>
<div class="line"><a name="l00095"></a><span class="lineno"> 95</span> <span class="comment"> */</span></div>
<div class="line"><a name="l00096"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a1ff87eaff39dcb007f79ed595f7cf7d3"> 96</a></span>  <span class="keywordtype">void</span> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a1ff87eaff39dcb007f79ed595f7cf7d3" title="install new taps.">set_taps</a>(<span class="keyword">const</span> std::vector<tap_type> &fftaps,</div>
<div class="line"><a name="l00097"></a><span class="lineno"> 97</span>  <span class="keyword">const</span> std::vector<tap_type> &fbtaps) <span class="keywordflow">throw</span> (std::invalid_argument)</div>
<div class="line"><a name="l00098"></a><span class="lineno"> 98</span>  {</div>
<div class="line"><a name="l00099"></a><span class="lineno"> 99</span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a9871f95fae0caa9591c4a6efead64528">d_latest_n</a> = 0;</div>
<div class="line"><a name="l00100"></a><span class="lineno"> 100</span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a4363ff21e735805cba8d74331d6bed21">d_latest_m</a> = 0;</div>
<div class="line"><a name="l00101"></a><span class="lineno"> 101</span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a903e4f9873bdd2946b8bc010dee0549f">d_fftaps</a> = fftaps;</div>
<div class="line"><a name="l00102"></a><span class="lineno"> 102</span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#adf311b2c19a1891e27a8e59d22f8cd54">d_fbtaps</a> = fbtaps;</div>
<div class="line"><a name="l00103"></a><span class="lineno"> 103</span> </div>
<div class="line"><a name="l00104"></a><span class="lineno"> 104</span>  <span class="keywordtype">int</span> n = fftaps.size();</div>
<div class="line"><a name="l00105"></a><span class="lineno"> 105</span>  <span class="keywordtype">int</span> m = fbtaps.size();</div>
<div class="line"><a name="l00106"></a><span class="lineno"> 106</span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a149e69591643e8ace02c74fd3f94f2a5">d_prev_input</a>.resize(2 * n);</div>
<div class="line"><a name="l00107"></a><span class="lineno"> 107</span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#ada105c79b12b9304843f7f209b009172">d_prev_output</a>.resize(2 * m);</div>
<div class="line"><a name="l00108"></a><span class="lineno"> 108</span> </div>
<div class="line"><a name="l00109"></a><span class="lineno"> 109</span>  <span class="keywordflow">for</span>(<span class="keywordtype">int</span> i = 0; i < 2 * n; i++) {</div>
<div class="line"><a name="l00110"></a><span class="lineno"> 110</span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a149e69591643e8ace02c74fd3f94f2a5">d_prev_input</a>[i] = 0;</div>
<div class="line"><a name="l00111"></a><span class="lineno"> 111</span>  }</div>
<div class="line"><a name="l00112"></a><span class="lineno"> 112</span>  <span class="keywordflow">for</span>(<span class="keywordtype">int</span> i = 0; i < 2 * m; i++) {</div>
<div class="line"><a name="l00113"></a><span class="lineno"> 113</span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#ada105c79b12b9304843f7f209b009172">d_prev_output</a>[i] = 0;</div>
<div class="line"><a name="l00114"></a><span class="lineno"> 114</span>  }</div>
<div class="line"><a name="l00115"></a><span class="lineno"> 115</span>  }</div>
<div class="line"><a name="l00116"></a><span class="lineno"> 116</span> </div>
<div class="line"><a name="l00117"></a><span class="lineno"> 117</span>  <span class="keyword">protected</span>:</div>
<div class="line"><a name="l00118"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a903e4f9873bdd2946b8bc010dee0549f"> 118</a></span>  std::vector<tap_type> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a903e4f9873bdd2946b8bc010dee0549f">d_fftaps</a>;</div>
<div class="line"><a name="l00119"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#adf311b2c19a1891e27a8e59d22f8cd54"> 119</a></span>  std::vector<tap_type> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#adf311b2c19a1891e27a8e59d22f8cd54">d_fbtaps</a>;</div>
<div class="line"><a name="l00120"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a9871f95fae0caa9591c4a6efead64528"> 120</a></span>  <span class="keywordtype">int</span> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a9871f95fae0caa9591c4a6efead64528">d_latest_n</a>;</div>
<div class="line"><a name="l00121"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a4363ff21e735805cba8d74331d6bed21"> 121</a></span>  <span class="keywordtype">int</span> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a4363ff21e735805cba8d74331d6bed21">d_latest_m</a>;</div>
<div class="line"><a name="l00122"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#ada105c79b12b9304843f7f209b009172"> 122</a></span>  std::vector<tap_type> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#ada105c79b12b9304843f7f209b009172">d_prev_output</a>;</div>
<div class="line"><a name="l00123"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a149e69591643e8ace02c74fd3f94f2a5"> 123</a></span>  std::vector<i_type> <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a149e69591643e8ace02c74fd3f94f2a5">d_prev_input</a>;</div>
<div class="line"><a name="l00124"></a><span class="lineno"> 124</span>  };</div>
<div class="line"><a name="l00125"></a><span class="lineno"> 125</span> </div>
<div class="line"><a name="l00126"></a><span class="lineno"> 126</span>  <span class="comment">//</span></div>
<div class="line"><a name="l00127"></a><span class="lineno"> 127</span>  <span class="comment">// general case. We may want to specialize this</span></div>
<div class="line"><a name="l00128"></a><span class="lineno"> 128</span>  <span class="comment">//</span></div>
<div class="line"><a name="l00129"></a><span class="lineno"> 129</span>  <span class="keyword">template</span><<span class="keyword">class</span> i_type, <span class="keyword">class</span> o_type, <span class="keyword">class</span> tap_type></div>
<div class="line"><a name="l00130"></a><span class="lineno"> 130</span>  o_type</div>
<div class="line"><a name="l00131"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a34b16ee180319b1398049e591fbd8d07"> 131</a></span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a34b16ee180319b1398049e591fbd8d07" title="compute a single output value.">iir_filter<i_type, o_type, tap_type>::filter</a>(<span class="keyword">const</span> i_type input)</div>
<div class="line"><a name="l00132"></a><span class="lineno"> 132</span>  {</div>
<div class="line"><a name="l00133"></a><span class="lineno"> 133</span>  tap_type acc;</div>
<div class="line"><a name="l00134"></a><span class="lineno"> 134</span>  <span class="keywordtype">unsigned</span> i = 0;</div>
<div class="line"><a name="l00135"></a><span class="lineno"> 135</span>  <span class="keywordtype">unsigned</span> n = ntaps_ff();</div>
<div class="line"><a name="l00136"></a><span class="lineno"> 136</span>  <span class="keywordtype">unsigned</span> m = ntaps_fb();</div>
<div class="line"><a name="l00137"></a><span class="lineno"> 137</span> </div>
<div class="line"><a name="l00138"></a><span class="lineno"> 138</span>  <span class="keywordflow">if</span>(n == 0)</div>
<div class="line"><a name="l00139"></a><span class="lineno"> 139</span>  <span class="keywordflow">return</span> (o_type)0;</div>
<div class="line"><a name="l00140"></a><span class="lineno"> 140</span> </div>
<div class="line"><a name="l00141"></a><span class="lineno"> 141</span>  <span class="keywordtype">int</span> latest_n = d_latest_n;</div>
<div class="line"><a name="l00142"></a><span class="lineno"> 142</span>  <span class="keywordtype">int</span> latest_m = d_latest_m;</div>
<div class="line"><a name="l00143"></a><span class="lineno"> 143</span> </div>
<div class="line"><a name="l00144"></a><span class="lineno"> 144</span>  acc = d_fftaps[0] * input;</div>
<div class="line"><a name="l00145"></a><span class="lineno"> 145</span>  <span class="keywordflow">for</span>(i = 1; i < n; i ++)</div>
<div class="line"><a name="l00146"></a><span class="lineno"> 146</span>  acc += (d_fftaps[i] * d_prev_input[latest_n + i]);</div>
<div class="line"><a name="l00147"></a><span class="lineno"> 147</span>  <span class="keywordflow">for</span>(i = 1; i < m; i ++)</div>
<div class="line"><a name="l00148"></a><span class="lineno"> 148</span>  acc += (d_fbtaps[i] * d_prev_output[latest_m + i]);</div>
<div class="line"><a name="l00149"></a><span class="lineno"> 149</span> </div>
<div class="line"><a name="l00150"></a><span class="lineno"> 150</span>  <span class="comment">// store the values twice to avoid having to handle wrap-around in the loop</span></div>
<div class="line"><a name="l00151"></a><span class="lineno"> 151</span>  d_prev_output[latest_m] = acc;</div>
<div class="line"><a name="l00152"></a><span class="lineno"> 152</span>  d_prev_output[latest_m+m] = acc;</div>
<div class="line"><a name="l00153"></a><span class="lineno"> 153</span>  d_prev_input[latest_n] = input;</div>
<div class="line"><a name="l00154"></a><span class="lineno"> 154</span>  d_prev_input[latest_n+n] = input;</div>
<div class="line"><a name="l00155"></a><span class="lineno"> 155</span> </div>
<div class="line"><a name="l00156"></a><span class="lineno"> 156</span>  latest_n--;</div>
<div class="line"><a name="l00157"></a><span class="lineno"> 157</span>  latest_m--;</div>
<div class="line"><a name="l00158"></a><span class="lineno"> 158</span>  <span class="keywordflow">if</span>(latest_n < 0)</div>
<div class="line"><a name="l00159"></a><span class="lineno"> 159</span>  latest_n += n;</div>
<div class="line"><a name="l00160"></a><span class="lineno"> 160</span>  <span class="keywordflow">if</span>(latest_m < 0)</div>
<div class="line"><a name="l00161"></a><span class="lineno"> 161</span>  latest_m += m;</div>
<div class="line"><a name="l00162"></a><span class="lineno"> 162</span> </div>
<div class="line"><a name="l00163"></a><span class="lineno"> 163</span>  d_latest_m = latest_m;</div>
<div class="line"><a name="l00164"></a><span class="lineno"> 164</span>  d_latest_n = latest_n;</div>
<div class="line"><a name="l00165"></a><span class="lineno"> 165</span>  <span class="keywordflow">return</span> (o_type)acc;</div>
<div class="line"><a name="l00166"></a><span class="lineno"> 166</span>  }</div>
<div class="line"><a name="l00167"></a><span class="lineno"> 167</span> </div>
<div class="line"><a name="l00168"></a><span class="lineno"> 168</span>  <span class="keyword">template</span><<span class="keyword">class</span> i_type, <span class="keyword">class</span> o_type, <span class="keyword">class</span> tap_type></div>
<div class="line"><a name="l00169"></a><span class="lineno"> 169</span>  <span class="keywordtype">void</span></div>
<div class="line"><a name="l00170"></a><span class="lineno"><a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a8549335490780d0d59f86908f2675d78"> 170</a></span>  <a class="code" href="classgr_1_1filter_1_1kernel_1_1iir__filter.html#a8549335490780d0d59f86908f2675d78" title="compute an array of N output values. input must have N valid entries.">iir_filter<i_type, o_type, tap_type>::filter_n</a>(o_type output[],</div>
<div class="line"><a name="l00171"></a><span class="lineno"> 171</span>  <span class="keyword">const</span> i_type input[],</div>
<div class="line"><a name="l00172"></a><span class="lineno"> 172</span>  <span class="keywordtype">long</span> n)</div>
<div class="line"><a name="l00173"></a><span class="lineno"> 173</span>  {</div>
<div class="line"><a name="l00174"></a><span class="lineno"> 174</span>  <span class="keywordflow">for</span>(<span class="keywordtype">int</span> i = 0; i < n; i++)</div>
<div class="line"><a name="l00175"></a><span class="lineno"> 175</span>  output[i] = filter(input[i]);</div>
<div class="line"><a name="l00176"></a><span class="lineno"> 176</span>  }</div>
<div class="line"><a name="l00177"></a><span class="lineno"> 177</span> </div>
<div class="line"><a name="l00178"></a><span class="lineno"> 178</span>  } <span class="comment">/* namespace kernel */</span></div>
<div class="line"><a name="l00179"></a><span class="lineno"> 179</span>  } <span class="comment">/* namespace filter */</span></div>
<div class="line"><a name="l00180"></a><span class="lineno"> 180</span> } <span class="comment">/* namespace gr */</span></div>
<div class="line"><a name="l00181"></a><span class="lineno"> 181</span> </div>
<div class="line"><a name="l00182"></a><span class="lineno"> 182</span> <span class="preprocessor">#endif </span><span class="comment">/* INCLUDED_IIR_FILTER_H */</span><span class="preprocessor"></span></div>
<div class="line"><a name="l00183"></a><span class="lineno"> 183</span> <span class="preprocessor"></span></div>
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