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<h1>gri_lfsr.h</h1> </div>
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<a href="gri__lfsr_8h.html">Go to the documentation of this file.</a><div class="fragment"><pre class="fragment"><a name="l00001"></a>00001 <span class="comment">/* -*- c++ -*- */</span>
<a name="l00002"></a>00002 <span class="comment">/*</span>
<a name="l00003"></a>00003 <span class="comment"> * Copyright 2008 Free Software Foundation, Inc.</span>
<a name="l00004"></a>00004 <span class="comment"> * </span>
<a name="l00005"></a>00005 <span class="comment"> * This file is part of GNU Radio</span>
<a name="l00006"></a>00006 <span class="comment"> * </span>
<a name="l00007"></a>00007 <span class="comment"> * GNU Radio is free software; you can redistribute it and/or modify</span>
<a name="l00008"></a>00008 <span class="comment"> * it under the terms of the GNU General Public License as published by</span>
<a name="l00009"></a>00009 <span class="comment"> * the Free Software Foundation; either version 3, or (at your option)</span>
<a name="l00010"></a>00010 <span class="comment"> * any later version.</span>
<a name="l00011"></a>00011 <span class="comment"> * </span>
<a name="l00012"></a>00012 <span class="comment"> * GNU Radio is distributed in the hope that it will be useful,</span>
<a name="l00013"></a>00013 <span class="comment"> * but WITHOUT ANY WARRANTY; without even the implied warranty of</span>
<a name="l00014"></a>00014 <span class="comment"> * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the</span>
<a name="l00015"></a>00015 <span class="comment"> * GNU General Public License for more details.</span>
<a name="l00016"></a>00016 <span class="comment"> * </span>
<a name="l00017"></a>00017 <span class="comment"> * You should have received a copy of the GNU General Public License</span>
<a name="l00018"></a>00018 <span class="comment"> * along with GNU Radio; see the file COPYING. If not, write to</span>
<a name="l00019"></a>00019 <span class="comment"> * the Free Software Foundation, Inc., 51 Franklin Street,</span>
<a name="l00020"></a>00020 <span class="comment"> * Boston, MA 02110-1301, USA.</span>
<a name="l00021"></a>00021 <span class="comment"> */</span>
<a name="l00022"></a>00022
<a name="l00023"></a>00023 <span class="preprocessor">#ifndef INCLUDED_GRI_LFSR_H</span>
<a name="l00024"></a>00024 <span class="preprocessor"></span><span class="preprocessor">#define INCLUDED_GRI_LFSR_H</span>
<a name="l00025"></a>00025 <span class="preprocessor"></span>
<a name="l00026"></a>00026 <span class="preprocessor">#include <stdexcept></span>
<a name="l00027"></a>00027 <span class="preprocessor">#include <stdint.h></span>
<a name="l00028"></a>00028 <span class="comment"></span>
<a name="l00029"></a>00029 <span class="comment">/*!</span>
<a name="l00030"></a>00030 <span class="comment"> * \brief Fibonacci Linear Feedback Shift Register using specified polynomial mask</span>
<a name="l00031"></a>00031 <span class="comment"> * \ingroup misc</span>
<a name="l00032"></a>00032 <span class="comment"> *</span>
<a name="l00033"></a>00033 <span class="comment"> * Generates a maximal length pseudo-random sequence of length 2^degree-1</span>
<a name="l00034"></a>00034 <span class="comment"> * </span>
<a name="l00035"></a>00035 <span class="comment"> * Constructor: gri_lfsr(int mask, int seed, int reg_len);</span>
<a name="l00036"></a>00036 <span class="comment"> * </span>
<a name="l00037"></a>00037 <span class="comment"> * mask - polynomial coefficients representing the locations</span>
<a name="l00038"></a>00038 <span class="comment"> * of feedback taps from a shift register which are xor'ed</span>
<a name="l00039"></a>00039 <span class="comment"> * together to form the new high order bit.</span>
<a name="l00040"></a>00040 <span class="comment"> *</span>
<a name="l00041"></a>00041 <span class="comment"> * Some common masks might be:</span>
<a name="l00042"></a>00042 <span class="comment"> * x^4 + x^3 + x^0 = 0x19</span>
<a name="l00043"></a>00043 <span class="comment"> * x^5 + x^3 + x^0 = 0x29</span>
<a name="l00044"></a>00044 <span class="comment"> * x^6 + x^5 + x^0 = 0x61</span>
<a name="l00045"></a>00045 <span class="comment"> *</span>
<a name="l00046"></a>00046 <span class="comment"> * seed - the initialization vector placed into the register</span>
<a name="l00047"></a>00047 <span class="comment"> * durring initialization. Low order bit corresponds</span>
<a name="l00048"></a>00048 <span class="comment"> * to x^0 coefficient -- the first to be shifted as output.</span>
<a name="l00049"></a>00049 <span class="comment"> *</span>
<a name="l00050"></a>00050 <span class="comment"> * reg_len - specifies the length of the feedback shift register </span>
<a name="l00051"></a>00051 <span class="comment"> * to be used. Durring each iteration, the register</span>
<a name="l00052"></a>00052 <span class="comment"> * is rightshifted one and the new bit is placed in bit reg_len.</span>
<a name="l00053"></a>00053 <span class="comment"> * reg_len should generally be at least order(mask) + 1</span>
<a name="l00054"></a>00054 <span class="comment"> *</span>
<a name="l00055"></a>00055 <span class="comment"> *</span>
<a name="l00056"></a>00056 <span class="comment"> * see http://en.wikipedia.org/wiki/Linear_feedback_shift_register </span>
<a name="l00057"></a>00057 <span class="comment"> * for more explanation.</span>
<a name="l00058"></a>00058 <span class="comment"> *</span>
<a name="l00059"></a>00059 <span class="comment"> *</span>
<a name="l00060"></a>00060 <span class="comment"> *</span>
<a name="l00061"></a>00061 <span class="comment"> * next_bit() - Standard LFSR operation</span>
<a name="l00062"></a>00062 <span class="comment"> * </span>
<a name="l00063"></a>00063 <span class="comment"> * Perform one cycle of the LFSR. The output bit is taken from</span>
<a name="l00064"></a>00064 <span class="comment"> * the shift register LSB. The shift register MSB is assigned from</span>
<a name="l00065"></a>00065 <span class="comment"> * the modulo 2 sum of the masked shift register.</span>
<a name="l00066"></a>00066 <span class="comment"> * </span>
<a name="l00067"></a>00067 <span class="comment"> * next_bit_scramble(unsigned char input) - Scramble an input stream</span>
<a name="l00068"></a>00068 <span class="comment"> * </span>
<a name="l00069"></a>00069 <span class="comment"> * Perform one cycle of the LFSR. The output bit is taken from</span>
<a name="l00070"></a>00070 <span class="comment"> * the shift register LSB. The shift register MSB is assigned from</span>
<a name="l00071"></a>00071 <span class="comment"> * the modulo 2 sum of the masked shift register and the input LSB.</span>
<a name="l00072"></a>00072 <span class="comment"> *</span>
<a name="l00073"></a>00073 <span class="comment"> * next_bit_descramble(unsigned char input) - Descramble an input stream</span>
<a name="l00074"></a>00074 <span class="comment"> *</span>
<a name="l00075"></a>00075 <span class="comment"> * Perform one cycle of the LFSR. The output bit is taken from </span>
<a name="l00076"></a>00076 <span class="comment"> * the modulo 2 sum of the masked shift register and the input LSB.</span>
<a name="l00077"></a>00077 <span class="comment"> * The shift register MSB is assigned from the LSB of the input.</span>
<a name="l00078"></a>00078 <span class="comment"> *</span>
<a name="l00079"></a>00079 <span class="comment"> * See http://en.wikipedia.org/wiki/Scrambler for operation of these</span>
<a name="l00080"></a>00080 <span class="comment"> * last two functions (see multiplicative scrambler.)</span>
<a name="l00081"></a>00081 <span class="comment"> *</span>
<a name="l00082"></a>00082 <span class="comment"> */</span>
<a name="l00083"></a>00083
<a name="l00084"></a><a class="code" href="classgri__lfsr.html">00084</a> <span class="keyword">class </span><a class="code" href="classgri__lfsr.html" title="Fibonacci Linear Feedback Shift Register using specified polynomial maskGenerates a maximal length ps...">gri_lfsr</a>
<a name="l00085"></a>00085 {
<a name="l00086"></a>00086 <span class="keyword">private</span>:
<a name="l00087"></a>00087 uint32_t d_shift_register;
<a name="l00088"></a>00088 uint32_t d_mask;
<a name="l00089"></a>00089 uint32_t d_shift_register_length; <span class="comment">// less than 32</span>
<a name="l00090"></a>00090
<a name="l00091"></a>00091 <span class="keyword">static</span> uint32_t
<a name="l00092"></a>00092 popCount(uint32_t x)
<a name="l00093"></a>00093 {
<a name="l00094"></a>00094 uint32_t r = x - ((x >> 1) & 033333333333)
<a name="l00095"></a>00095 - ((x >> 2) & 011111111111);
<a name="l00096"></a>00096 <span class="keywordflow">return</span> ((r + (r >> 3)) & 030707070707) % 63;
<a name="l00097"></a>00097 }
<a name="l00098"></a>00098
<a name="l00099"></a>00099 <span class="keyword">public</span>:
<a name="l00100"></a>00100
<a name="l00101"></a><a class="code" href="classgri__lfsr.html#a9d75c0d9937724f0784ccbae11114950">00101</a> <a class="code" href="classgri__lfsr.html#a9d75c0d9937724f0784ccbae11114950">gri_lfsr</a>(uint32_t <a class="code" href="classgri__lfsr.html#ab11f525cf4205ac9e77ed3b23d353812">mask</a>, uint32_t seed, uint32_t reg_len)
<a name="l00102"></a>00102 : d_shift_register(seed), d_mask(mask), d_shift_register_length(reg_len)
<a name="l00103"></a>00103 {
<a name="l00104"></a>00104 <span class="keywordflow">if</span> (reg_len > 31)
<a name="l00105"></a>00105 <span class="keywordflow">throw</span> std::invalid_argument(<span class="stringliteral">"reg_len must be <= 31"</span>);
<a name="l00106"></a>00106 }
<a name="l00107"></a>00107
<a name="l00108"></a><a class="code" href="classgri__lfsr.html#ab48a354944fe18d9d261be11aa558b0f">00108</a> <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> <a class="code" href="classgri__lfsr.html#ab48a354944fe18d9d261be11aa558b0f">next_bit</a>() {
<a name="l00109"></a>00109 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> output = d_shift_register & 1;
<a name="l00110"></a>00110 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> newbit = popCount( d_shift_register & d_mask )%2;
<a name="l00111"></a>00111 d_shift_register = ((d_shift_register>>1) | (newbit<<d_shift_register_length));
<a name="l00112"></a>00112 <span class="keywordflow">return</span> output;
<a name="l00113"></a>00113 }
<a name="l00114"></a>00114
<a name="l00115"></a><a class="code" href="classgri__lfsr.html#afd1989999dcc0306a1b73f5822d38357">00115</a> <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> <a class="code" href="classgri__lfsr.html#afd1989999dcc0306a1b73f5822d38357">next_bit_scramble</a>(<span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> input) {
<a name="l00116"></a>00116 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> output = d_shift_register & 1;
<a name="l00117"></a>00117 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> newbit = (popCount( d_shift_register & d_mask )%2)^(input & 1);
<a name="l00118"></a>00118 d_shift_register = ((d_shift_register>>1) | (newbit<<d_shift_register_length));
<a name="l00119"></a>00119 <span class="keywordflow">return</span> output;
<a name="l00120"></a>00120 }
<a name="l00121"></a>00121
<a name="l00122"></a><a class="code" href="classgri__lfsr.html#af23672b2652cbfa71cd34d99b5b3edd2">00122</a> <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> <a class="code" href="classgri__lfsr.html#af23672b2652cbfa71cd34d99b5b3edd2">next_bit_descramble</a>(<span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> input) {
<a name="l00123"></a>00123 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> output = (popCount( d_shift_register & d_mask )%2)^(input & 1);
<a name="l00124"></a>00124 <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> newbit = input & 1;
<a name="l00125"></a>00125 d_shift_register = ((d_shift_register>>1) | (newbit<<d_shift_register_length));
<a name="l00126"></a>00126 <span class="keywordflow">return</span> output;
<a name="l00127"></a>00127 }
<a name="l00128"></a>00128
<a name="l00129"></a>00129 <span class="comment"></span>
<a name="l00130"></a>00130 <span class="comment"> /*!</span>
<a name="l00131"></a>00131 <span class="comment"> * Rotate the register through x number of bits</span>
<a name="l00132"></a>00132 <span class="comment"> * where we are just throwing away the results to get queued up correctly</span>
<a name="l00133"></a>00133 <span class="comment"> */</span>
<a name="l00134"></a><a class="code" href="classgri__lfsr.html#af04de11f558b49d79265df6f32f343c1">00134</a> <span class="keywordtype">void</span> <a class="code" href="classgri__lfsr.html#af04de11f558b49d79265df6f32f343c1">pre_shift</a>(<span class="keywordtype">int</span> num){
<a name="l00135"></a>00135 <span class="keywordflow">for</span>(<span class="keywordtype">int</span> i=0; i<num; i++){
<a name="l00136"></a>00136 <a class="code" href="classgri__lfsr.html#ab48a354944fe18d9d261be11aa558b0f">next_bit</a>();
<a name="l00137"></a>00137 }
<a name="l00138"></a>00138 }
<a name="l00139"></a>00139
<a name="l00140"></a><a class="code" href="classgri__lfsr.html#ab11f525cf4205ac9e77ed3b23d353812">00140</a> <span class="keywordtype">int</span> <a class="code" href="classgri__lfsr.html#ab11f525cf4205ac9e77ed3b23d353812">mask</a>()<span class="keyword"> const </span>{ <span class="keywordflow">return</span> d_mask; }
<a name="l00141"></a>00141 };
<a name="l00142"></a>00142
<a name="l00143"></a>00143 <span class="preprocessor">#endif </span><span class="comment">/* INCLUDED_GRI_LFSR_H */</span>
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