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424c74d006
Remove the paragraph about writing to the Free Software Foundation's mailing address. The FSF has changed addresses in the past, and may do so again. In 2021 this is not useful, let's rather have a bit less boilerplate at the start of source files. Change-Id: I8ba71ab9ccde4ba25151ecbeb2a323f706b57d43
109 lines
2.8 KiB
C++
109 lines
2.8 KiB
C++
/*
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* Copyright (C) 2017 Alexander Chemeris <Alexander.Chemeris@fairwaves.co>
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*
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* SPDX-License-Identifier: LGPL-2.1+
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*/
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#ifndef PRBS_H
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#define PRBS_H
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#include <stdint.h>
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#include <assert.h>
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/** Pseudo-random binary sequence (PRBS) generator (a Galois LFSR implementation). */
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class PRBS {
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public:
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PRBS(unsigned wLen, uint64_t wCoeff, uint64_t wState = 0x01)
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: mCoeff(wCoeff), mStartState(wState), mState(wState), mLen(wLen)
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{ assert(wLen<=64); }
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/**@name Accessors */
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//@{
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uint64_t coeff() const { return mCoeff; }
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uint64_t state() const { return mState; }
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void state(uint64_t state) { mState = state & mask(); }
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unsigned size() const { return mLen; }
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//@}
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/**
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Calculate one bit of a PRBS
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*/
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unsigned generateBit()
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{
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const unsigned result = mState & 0x01;
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processBit(result);
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return result;
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}
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/**
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Update the generator state by one bit.
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If you want to synchronize your PRBS to a known state, call this function
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size() times passing your PRBS to it bit by bit.
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*/
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void processBit(unsigned inBit)
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{
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mState >>= 1;
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if (inBit) mState ^= mCoeff;
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}
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/** Return true when PRBS is wrapping through initial state */
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bool isFinished() const { return mStartState == mState; }
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protected:
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uint64_t mCoeff; ///< polynomial coefficients. LSB is zero exponent.
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uint64_t mStartState; ///< initial shift register state.
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uint64_t mState; ///< shift register state.
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unsigned mLen; ///< number of bits used in shift register
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/** Return mask for the state register */
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uint64_t mask() const { return (mLen==64)?0xFFFFFFFFFFFFFFFFUL:((1<<mLen)-1); }
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};
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/**
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A standard 9-bit based pseudorandom binary sequence (PRBS) generator.
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Polynomial: x^9 + x^5 + 1
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*/
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class PRBS9 : public PRBS {
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public:
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PRBS9(uint64_t wState = 0x01)
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: PRBS(9, 0x0110, wState)
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{}
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};
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/**
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A standard 15-bit based pseudorandom binary sequence (PRBS) generator.
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Polynomial: x^15 + x^14 + 1
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*/
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class PRBS15 : public PRBS {
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public:
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PRBS15(uint64_t wState = 0x01)
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: PRBS(15, 0x6000, wState)
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{}
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};
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/**
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A standard 64-bit based pseudorandom binary sequence (PRBS) generator.
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Polynomial: x^64 + x^63 + x^61 + x^60 + 1
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*/
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class PRBS64 : public PRBS {
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public:
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PRBS64(uint64_t wState = 0x01)
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: PRBS(64, 0xD800000000000000ULL, wState)
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{}
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};
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#endif // PRBS_H
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