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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