mayhem-firmware/firmware/common/lfsr_random.cpp

/*
 * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
 *
 * This file is part of PortaPack.
 *
 * This program 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 2, or (at your option)
 * any later version.
 *
 * This program 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 this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include "lfsr_random.hpp"

static void lfsr_iterate_internal(lfsr_word_t& v) {
    /*
            Generated with lfsr-generator:
            http://lfsr-generator.sourceforge.net
            =============================================
                config          : fibonacci
                length          : 31
                taps            : (31, 18)
                shift-amounts   : (12, 12, 8)
                shift-direction : left
        */
    enum {
        length = 31,
        tap_0 = 31,
        tap_1 = 18,
        shift_amount_0 = 12,
        shift_amount_1 = 12,
        shift_amount_2 = 8
    };

    const lfsr_word_t zero = 0;
    v = ((
             v << shift_amount_0) |
         ((
              (v >> (tap_0 - shift_amount_0)) ^
              (v >> (tap_1 - shift_amount_0))) &
          (~(~zero << shift_amount_0))));
    v = ((
             v << shift_amount_1) |
         ((
              (v >> (tap_0 - shift_amount_1)) ^
              (v >> (tap_1 - shift_amount_1))) &
          (~(~zero << shift_amount_1))));
    v = ((
             v << shift_amount_2) |
         ((
              (v >> (tap_0 - shift_amount_2)) ^
              (v >> (tap_1 - shift_amount_2))) &
          (~(~zero << shift_amount_2))));
}

lfsr_word_t lfsr_iterate(lfsr_word_t v) {
    lfsr_iterate_internal(v);
    return v;
}

void lfsr_fill(lfsr_word_t& v, lfsr_word_t* buffer, size_t word_count) {
    while (word_count != 0) {
        lfsr_iterate_internal(v);
        *(buffer++) = v;
        word_count--;
    }
}

bool lfsr_compare(lfsr_word_t& v, const lfsr_word_t* buffer, size_t word_count) {
    while (word_count != 0) {
        lfsr_iterate_internal(v);
        if (*(buffer++) != v) {
            return false;
        }
        word_count--;
    }
    return true;
}