GNU Radio 3.5.3.2 C++ API
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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>
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 |
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.)
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