LFSR

An efficient linear feedback shift register (LFSR) class written in C++

How to use this library ?

Copy LFSR.c and LFSR.h to your project and import the library :

#include "LFSR.h"

To create an LFSR : (by default all bits are set to 0. Here a 15 bits LFSR is created)

LFSR lfsr(15);

To initialize the LFSR, the first bit is set to 1

lfsr.setBit(0, true);

To perform a right shift with X0 xor X1 as feedback (X15 + X14 + 1 in polynomial notation)

lfsr.rightShift(lfsr.getFirstBit() xor lfsr.getBit(1) xor lfsr.getBit(4));

Display first 8-bit of the LFSR :

lfsr.get8bit()

All functionalities explained :

Get the size in bit of the register :

uint32_t getSize();

Get the raw value of the

uint32_t getArrayElement(uint32_t bitPosition);

Get the size of internal 32-bit array used for the register

uint32_t getArraySize();

Perform a right shift

void rightShift(bool last);

Perform a left shift

void leftShift(bool first);

Get first 8-bit

uint8_t get8bit();

Get first 16-bit

uint16_t get16bit();

Get first 32-bit

uint32_t get32bit();

Get the value at a specific position in the internal 32-bit array used for the register

uint32_t get32bitArray(uint32_t position);

Get a specific bit :

bool getBit(uint32_t bitPosition);

Get the first bit (equivalent to getBit(0) :

bool getFirstBit();

Get the last bit :

bool getLastBit();

Set a specific bit

void setBit(uint32_t bitPosition, bool value);

Set the first bit (equivalent to setBit(0, value))

void setFirstBit(bool value);

Set the last bit

void setLastBit(bool value);

Save the content of the register to a buffer

void save(uint32_t * &output);

Compare the register to a saved register

bool compare(uint32_t * &output);

Restaure the register with a saved register

void set(uint32_t * &output);

Examples

The example calculates the length cycle of a 15 bits register with X15 + X14 + 1 as feedback

To build the sample :

g++ -std=c++11 LFSR.cpp main.cpp -o lfsr

Output of the sample is :

counter = 32767

Samples folder contains some use cases like A5/1 encryption