From: eb Date: Wed, 3 Sep 2008 16:12:06 +0000 (+0000) Subject: Fibonacci Linear Feedback Shift Register X-Git-Url: https://git.gag.com/?a=commitdiff_plain;h=b0d95cf81d7bb691012a13932e6aa6d19648b929;p=debian%2Fgnuradio Fibonacci Linear Feedback Shift Register git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@9492 221aa14e-8319-0410-a670-987f0aec2ac5 --- diff --git a/gnuradio-core/src/lib/general/Makefile.am b/gnuradio-core/src/lib/general/Makefile.am index c449a39b..2e3b16e4 100644 --- a/gnuradio-core/src/lib/general/Makefile.am +++ b/gnuradio-core/src/lib/general/Makefile.am @@ -176,7 +176,8 @@ libgeneral_qa_la_SOURCES = \ qa_gr_fxpt.cc \ qa_gr_fxpt_nco.cc \ qa_gr_fxpt_vco.cc \ - qa_gr_math.cc + qa_gr_math.cc \ + qa_gri_lfsr.cc grinclude_HEADERS = \ gr_agc_cc.h \ diff --git a/gnuradio-core/src/lib/general/gri_lfsr.h b/gnuradio-core/src/lib/general/gri_lfsr.h new file mode 100644 index 00000000..c11eb048 --- /dev/null +++ b/gnuradio-core/src/lib/general/gri_lfsr.h @@ -0,0 +1,104 @@ +/* -*- c++ -*- */ +/* + * Copyright 2007 Free Software Foundation, Inc. + * + * This file is part of GNU Radio + * + * GNU Radio is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 3, or (at your option) + * any later version. + * + * GNU Radio is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with GNU Radio; see the file COPYING. If not, write to + * the Free Software Foundation, Inc., 51 Franklin Street, + * Boston, MA 02110-1301, USA. + */ + +#ifndef INCLUDED_GRI_LFSR_H +#define INCLUDED_GRI_LFSR_H + +#include +#include + +/*! + * \brief Fibonacci Linear Feedback Shift Register using specified polynomial mask + * \ingroup math + * + * Generates a maximal length pseudo-random sequence of length 2^degree-1 + * + * Constructor: gri_lfsr(int mask, int seed, int reg_len); + * + * mask - polynomial coefficients representing the locations + * of feedback taps from a shift register which are xor'ed + * together to form the new high order bit. + * + * Some common masks might be: + * x^4 + x^3 + x^0 = 0x19 + * x^5 + x^3 + x^0 = 0x29 + * x^6 + x^5 + x^0 = 0x61 + * + * seed - the initialization vector placed into the register + * durring initialization. Low order bit corresponds + * to x^0 coefficient -- the first to be shifted as output. + * + * reg_len - specifies the length of the feedback shift register + * to be used. Durring each iteration, the register + * is rightshifted one and the new bit is placed in bit reg_len. + * reg_len should generally be at least order(mask) + 1 + * + * + * see http://en.wikipedia.org/wiki/Linear_feedback_shift_register + * for more explanation. + * + * + * + * next_bit() - performs once cycle of the lfsr, + * generating the new high order bit from the mask + * and returning the low order bit which has been + * shifted out of the register. + * + * + */ + + +class gri_lfsr +{ + private: + uint32_t d_shift_register; + uint32_t d_mask; + uint32_t d_shift_register_length; // less than 32 + + static uint32_t + popCount(uint32_t x) + { + uint32_t r = x - ((x >> 1) & 033333333333) + - ((x >> 2) & 011111111111); + return ((r + (r >> 3)) & 030707070707) % 63; + } + + public: + + gri_lfsr(uint32_t mask, uint32_t seed, uint32_t reg_len) + : d_shift_register(seed), d_mask(mask), d_shift_register_length(reg_len) + { + if (reg_len > 31) + throw std::invalid_argument("reg_len must be <= 31"); + } + + unsigned char next_bit() { + unsigned char bit = d_shift_register & 1; + unsigned char newbit = popCount( d_shift_register & d_mask )%2; + d_shift_register = ((d_shift_register>>1) | (newbit< #include #include +#include CppUnit::TestSuite * qa_general::suite () @@ -44,6 +45,7 @@ qa_general::suite () s->addTest (qa_gr_fxpt_nco::suite ()); s->addTest (qa_gr_fxpt_vco::suite ()); s->addTest (qa_gr_math::suite ()); + s->addTest (qa_gri_lfsr::suite ()); return s; } diff --git a/gnuradio-core/src/lib/general/qa_gri_lfsr.cc b/gnuradio-core/src/lib/general/qa_gri_lfsr.cc new file mode 100644 index 00000000..9a72bf8d --- /dev/null +++ b/gnuradio-core/src/lib/general/qa_gri_lfsr.cc @@ -0,0 +1,56 @@ +/* + * Copyright 2008 Free Software Foundation, Inc. + * + * This file is part of GNU Radio + * + * GNU Radio is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 3, or (at your option) + * any later version. + * + * GNU Radio is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with GNU Radio; see the file COPYING. If not, write to + * the Free Software Foundation, Inc., 51 Franklin Street, + * Boston, MA 02110-1301, USA. + */ + +#include +#include +#include +#include + +void +qa_gri_lfsr::test_lfsr () +{ + int mask = 0x19; + int seed = 0x01; + int length = 5; + + gri_lfsr lfsr1(mask,seed,length); + gri_lfsr lfsr2(mask,seed,length); + + unsigned char expected[] = {1, 0, 1, 1, 0, 1, 0, 1, 0, 0}; + + for(unsigned int i=0; i<31; i++){ + lfsr1.next_bit(); + } + + // test that after one lfsr cycle we still match out uncycled lfsr + for (unsigned int i = 0; i < 41; i++) { + CPPUNIT_ASSERT_EQUAL((int) lfsr1.next_bit(), (int) lfsr2.next_bit()); + } + + // test the known correct values at the given shift offset + for(unsigned int i=0; i<10; i++){ + CPPUNIT_ASSERT_EQUAL((int) lfsr1.next_bit(), (int) expected[i]); + } + + // test for register length too long + CPPUNIT_ASSERT_THROW(gri_lfsr(mask, seed, 32), std::invalid_argument); +} + diff --git a/gnuradio-core/src/lib/general/qa_gri_lfsr.h b/gnuradio-core/src/lib/general/qa_gri_lfsr.h new file mode 100644 index 00000000..f65943a9 --- /dev/null +++ b/gnuradio-core/src/lib/general/qa_gri_lfsr.h @@ -0,0 +1,38 @@ +/* -*- c++ -*- */ +/* + * Copyright 2008 Free Software Foundation, Inc. + * + * This file is part of GNU Radio + * + * GNU Radio is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 3, or (at your option) + * any later version. + * + * GNU Radio is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with GNU Radio; see the file COPYING. If not, write to + * the Free Software Foundation, Inc., 51 Franklin Street, + * Boston, MA 02110-1301, USA. + */ +#ifndef _QA_GRI_LFSR_H_ +#define _QA_GRI_LFSR_H_ + +#include +#include + +class qa_gri_lfsr : public CppUnit::TestCase { + + CPPUNIT_TEST_SUITE(qa_gri_lfsr); + CPPUNIT_TEST(test_lfsr); + CPPUNIT_TEST_SUITE_END(); + + private: + void test_lfsr(); +}; + +#endif /* _QA_GRI_LFSR_H_ */