From cd8b03e45ff50f6f65f57b2e62e70f725da638d4 Mon Sep 17 00:00:00 2001
From: Tom Rondeau <trondeau@vt.edu>
Date: Sat, 10 Nov 2012 16:25:30 -0500
Subject: analog: moved lfsr from gr-analog to gr-digital where it is used.
---
gr-digital/include/digital/CMakeLists.txt | 1 +
gr-digital/include/digital/lfsr.h | 162 ++++++++++++++++++++++++++++++
2 files changed, 163 insertions(+)
create mode 100644 gr-digital/include/digital/lfsr.h
(limited to 'gr-digital/include/digital')
diff --git a/gr-digital/include/digital/CMakeLists.txt b/gr-digital/include/digital/CMakeLists.txt
index d8e17546ed..1a5869b3cd 100644
--- a/gr-digital/include/digital/CMakeLists.txt
+++ b/gr-digital/include/digital/CMakeLists.txt
@@ -78,6 +78,7 @@ install(FILES
api.h
constellation.h
crc32.h
+ lfsr.h
glfsr.h
mpsk_snr_est.h
simple_framer_sync.h
diff --git a/gr-digital/include/digital/lfsr.h b/gr-digital/include/digital/lfsr.h
new file mode 100644
index 0000000000..2319961257
--- /dev/null
+++ b/gr-digital/include/digital/lfsr.h
@@ -0,0 +1,162 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2008,2010,2012 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_DIGITAL_LFSR_H
+#define INCLUDED_DIGITAL_LFSR_H
+
+#include <digital/api.h>
+#include <stdexcept>
+#include <stdint.h>
+
+namespace gr {
+ namespace digital {
+
+ /*!
+ * \brief Fibonacci Linear Feedback Shift Register using specified
+ * polynomial mask
+ * \ingroup misc
+ *
+ * Generates a maximal length pseudo-random sequence of length
+ * 2^degree-1
+ *
+ * Constructor: digital::lfsr(int mask, int seed, int reg_len);
+ *
+ * \param 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
+ *
+ * \param 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.
+ *
+ * \param 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() - Standard LFSR operation
+ *
+ * Perform one cycle of the LFSR. The output bit is taken from
+ * the shift register LSB. The shift register MSB is assigned from
+ * the modulo 2 sum of the masked shift register.
+ *
+ * next_bit_scramble(unsigned char input) - Scramble an input stream
+ *
+ * Perform one cycle of the LFSR. The output bit is taken from
+ * the shift register LSB. The shift register MSB is assigned from
+ * the modulo 2 sum of the masked shift register and the input LSB.
+ *
+ * next_bit_descramble(unsigned char input) - Descramble an input stream
+ *
+ * Perform one cycle of the LFSR. The output bit is taken from
+ * the modulo 2 sum of the masked shift register and the input LSB.
+ * The shift register MSB is assigned from the LSB of the input.
+ *
+ * See http://en.wikipedia.org/wiki/Scrambler for operation of these
+ * last two functions (see multiplicative scrambler.)
+ */
+ class lfsr
+ {
+ private:
+ uint32_t d_shift_register;
+ uint32_t d_mask;
+ uint32_t d_seed;
+ 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:
+ lfsr(uint32_t mask, uint32_t seed, uint32_t reg_len)
+ : d_shift_register(seed),
+ d_mask(mask),
+ d_seed(seed),
+ 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 output = 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 output;
+ }
+
+ unsigned char next_bit_scramble(unsigned char input)
+ {
+ unsigned char output = d_shift_register & 1;
+ unsigned char newbit = (popCount( d_shift_register & d_mask )%2)^(input & 1);
+ d_shift_register = ((d_shift_register>>1) | (newbit<<d_shift_register_length));
+ return output;
+ }
+
+ unsigned char next_bit_descramble(unsigned char input)
+ {
+ unsigned char output = (popCount( d_shift_register & d_mask )%2)^(input & 1);
+ unsigned char newbit = input & 1;
+ d_shift_register = ((d_shift_register>>1) | (newbit<<d_shift_register_length));
+ return output;
+ }
+
+ /*!
+ * Reset shift register to initial seed value
+ */
+ void reset() { d_shift_register = d_seed; }
+
+ /*!
+ * Rotate the register through x number of bits
+ * where we are just throwing away the results to get queued up correctly
+ */
+ void pre_shift(int num)
+ {
+ for(int i=0; i<num; i++) {
+ next_bit();
+ }
+ }
+
+ int mask() const { return d_mask; }
+ };
+
+ } /* namespace digital */
+} /* namespace gr */
+
+#endif /* INCLUDED_DIGITAL_LFSR_H */
--
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