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/*
lsfr.cpp: Linear Feedback Shift Register opcode
Copyright (C) 2020 Dave Seidel
This file is part of Csound.
Based on code by Patrick Dowling in the Ornament & Crime firmware;
see original copyright notice below this one.
Original code may be found at:
https://github.com/mxmxmx/O_C/blob/master/software/o_c_REV/util/util_turing.h
The Csound Library is free software; you can redistribute it
and/or modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
Csound 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 Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with Csound; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
02110-1301 USA
*/
// ORIGINAL COPYRIGHT NOTICE
//
// Copyright (c) 2016 Patrick Dowling
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
/**
* Linear Feedback Shift Register (LFSR) opcode.
*
* Description
*
* Output is a series of pseudo-random positive integers. This is the technique
* used in so-called "Turing machine" synth modules and is usually used to
* generate melodic sequences. This implementation is adapted from the firmware
* for the Ornament & Crime module, as used in the Quantermain and Meta-Q apps.
*
* Syntax
*
* knum lfsr ilen, iprob [, iseed]
*
* knum = lfsr(ilen, iprob [, iseed])
*
* Initialization
*
* ilen -- length of shift register, valid values are 1-31 (inclusive). The
* larger the length, the larger the resulting integers in the output. You
* can use this to constrain the output to a suitable range.
*
* iprob -- probability, valid values 1-255 (inclusive). Controls the spread
* of the output; larger values result in a wider spread of values.
*
* iseed (optional, default -1) -- initial state of the shift register, as a
* pattern of bits. The value is treated as an unsigned integer, so the default
* of -1 is effectively all bits on (0b11111111...).
*
* Performance
*
* knum -- Integer output.
*/
#include <time.h>
#include <plugin.h>
struct LFSR : csnd::Plugin<1, 3> {
static constexpr char const *otypes = "k";
static constexpr char const *itypes = "iij";
uint8_t length_;
uint8_t probability_;
uint32_t shift_register_;
uint32_t _process() {
uint32_t shift_register = shift_register_;
// Toggle LSB; there might be better random options
if (255 == probability_ || static_cast<uint8_t>((rand() % (255 + 1)) < probability_)) {
shift_register ^= 0x1;
}
uint32_t lsb_mask = 0x1 << (length_ - 1);
if (shift_register & 0x1) {
shift_register = (shift_register >> 1) | lsb_mask;
} else {
shift_register = (shift_register >> 1) & ~lsb_mask;
}
// hack... don't turn all zero ...
if (!shift_register) {
shift_register |= ((rand() % (0x2 + 1)) << (length_ - 1));
}
shift_register_ = shift_register;
return shift_register & ~(0xffffffff << length_);
}
int init() {
srand(time(NULL));
length_ = inargs[0];
probability_ = inargs[1];
shift_register_ = in_count() == 3 ? inargs[2] : 0xffffffff;
return OK;
}
int kperf() {
outargs[0] = (int) _process();
return OK;
}
};
#include <modload.h>
void csnd::on_load(Csound *csound) {
csnd::plugin<LFSR>(csound, "lfsr", "k", "iij", csnd::thread::ik);
}
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