Fibonacci Linear Feedback Shift Register

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@9492 221aa14e-8319-0410-a670-987f0aec2ac5

5 files changed, 202 insertions, 1 deletions

diff --git a/gnuradio-core/src/lib/general/Makefile.am b/gnuradio-core/src/lib/general/Makefile.am
index c449a39b7..2e3b16e4e 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 000000000..c11eb048f
--- /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 <stdexcept>
+#include <stdint.h>
+
+/*!
+ * \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<<d_shift_register_length));
+    return bit;
+  }
+
+  int mask() const { return d_mask; }
+};
+
+#endif /* INCLUDED_GRI_LFSR_H */
diff --git a/gnuradio-core/src/lib/general/qa_general.cc b/gnuradio-core/src/lib/general/qa_general.cc
index 75d563236..6984d798c 100644
--- a/gnuradio-core/src/lib/general/qa_general.cc
+++ b/gnuradio-core/src/lib/general/qa_general.cc
@@ -32,6 +32,7 @@
 #include <qa_gr_fxpt_nco.h>
 #include <qa_gr_fxpt_vco.h>
 #include <qa_gr_math.h>
+#include <qa_gri_lfsr.h>
 
 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 000000000..9a72bf8d9
--- /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 <gri_lfsr.h>
+#include <qa_gri_lfsr.h>
+#include <cppunit/TestAssert.h>
+#include <stdio.h>
+
+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 000000000..f65943a90
--- /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 <cppunit/extensions/HelperMacros.h>
+#include <cppunit/TestCase.h>
+
+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_ */