gri_lfsr Class Reference

Fibonacci Linear Feedback Shift Register using specified polynomial maskGenerates a maximal length pseudo-random sequence of length 2^degree-1. More...

#include <gri_lfsr.h>

List of all members.

Public Member Functions
	gri_lfsr (uint32_t mask, uint32_t seed, uint32_t reg_len)
unsigned char	next_bit ()
unsigned char	next_bit_scramble (unsigned char input)
unsigned char	next_bit_descramble (unsigned char input)
void	reset ()
void	pre_shift (int num)
int	mask () const

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Detailed Description

Fibonacci Linear Feedback Shift Register using specified polynomial mask

Generates a maximal length pseudo-random sequence of length 2^degree-1.

Constructor: gri_lfsr(int mask, int seed, int reg_len);

mask - polynomial coefficients representing the locations of feedback taps from a shift register which are xor'ed together to form the new high order bit.

Some common masks might be: x^4 + x^3 + x^0 = 0x19 x^5 + x^3 + x^0 = 0x29 x^6 + x^5 + x^0 = 0x61

seed - the initialization vector placed into the register durring initialization. Low order bit corresponds to x^0 coefficient -- the first to be shifted as output.

reg_len - specifies the length of the feedback shift register to be used. Durring each iteration, the register is rightshifted one and the new bit is placed in bit reg_len. reg_len should generally be at least order(mask) + 1

see http://en.wikipedia.org/wiki/Linear_feedback_shift_register for more explanation.

next_bit() - Standard LFSR operation

Perform one cycle of the LFSR. The output bit is taken from the shift register LSB. The shift register MSB is assigned from the modulo 2 sum of the masked shift register.

next_bit_scramble(unsigned char input) - Scramble an input stream

Perform one cycle of the LFSR. The output bit is taken from the shift register LSB. The shift register MSB is assigned from the modulo 2 sum of the masked shift register and the input LSB.

next_bit_descramble(unsigned char input) - Descramble an input stream

Perform one cycle of the LFSR. The output bit is taken from the modulo 2 sum of the masked shift register and the input LSB. The shift register MSB is assigned from the LSB of the input.

See http://en.wikipedia.org/wiki/Scrambler for operation of these last two functions (see multiplicative scrambler.)

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Constructor & Destructor Documentation

gri_lfsr::gri_lfsr	(	uint32_t	mask,
		uint32_t	seed,
		uint32_t	reg_len
	)		[inline]

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Member Function Documentation

int gri_lfsr::mask

(

)

const [inline]

unsigned char gri_lfsr::next_bit

(

)

[inline]

unsigned char gri_lfsr::next_bit_descramble

(

unsigned char

input

)

[inline]

unsigned char gri_lfsr::next_bit_scramble

(

unsigned char

input

)

[inline]

void gri_lfsr::pre_shift

(

int

num

)

[inline]

Rotate the register through x number of bits where we are just throwing away the results to get queued up correctly

void gri_lfsr::reset

(

)

[inline]

Reset shift register to initial seed value

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The documentation for this class was generated from the following file:

• gri_lfsr.h