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Diffstat (limited to 'gr-digital/include/digital/lfsr.h')
| -rw-r--r-- | gr-digital/include/digital/lfsr.h | 163 |
1 files changed, 0 insertions, 163 deletions
diff --git a/gr-digital/include/digital/lfsr.h b/gr-digital/include/digital/lfsr.h deleted file mode 100644 index 0dd419b791..0000000000 --- a/gr-digital/include/digital/lfsr.h +++ /dev/null @@ -1,163 +0,0 @@ -/* -*- 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 - * - * \details - * 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 */ |