diff options
| author | jcorgan <jcorgan@221aa14e-8319-0410-a670-987f0aec2ac5> | 2008-09-12 02:54:22 +0000 |
|---|---|---|
| committer | jcorgan <jcorgan@221aa14e-8319-0410-a670-987f0aec2ac5> | 2008-09-12 02:54:22 +0000 |
| commit | c4763fb9f73df6832a015d84111cd2573a7b9bc6 (patch) | |
| tree | e2691291da9297b8ecb43b22e98ddbb972592ac8 /gnuradio-core/src/lib/general/gri_lfsr.h | |
| parent | 26e4afc44d2d0e77c2f6c41dff43555b3c9166e6 (diff) | |
Merged -r9556:9560 from jcorgan/scr into trunk. Adds gr.scrambler_bb and gr.descrambler_bb, using updated gri_lfsr.
git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@9561 221aa14e-8319-0410-a670-987f0aec2ac5
Diffstat (limited to 'gnuradio-core/src/lib/general/gri_lfsr.h')
| -rw-r--r-- | gnuradio-core/src/lib/general/gri_lfsr.h | 43 |
1 files changed, 36 insertions, 7 deletions
diff --git a/gnuradio-core/src/lib/general/gri_lfsr.h b/gnuradio-core/src/lib/general/gri_lfsr.h index 29873698c1..b6eee76793 100644 --- a/gnuradio-core/src/lib/general/gri_lfsr.h +++ b/gnuradio-core/src/lib/general/gri_lfsr.h @@ -58,15 +58,29 @@ * * * - * next_bit() - performs once cycle of the lfsr, - * generating the new high order bit from the mask - * and returning the low order bit which has been - * shifted out of the register. + * 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.) * */ - class gri_lfsr { private: @@ -92,12 +106,27 @@ class gri_lfsr } unsigned char next_bit() { - unsigned char bit = d_shift_register & 1; + unsigned char output = d_shift_register & 1; unsigned char newbit = popCount( d_shift_register & d_mask )%2; d_shift_register = ((d_shift_register>>1) | (newbit<<d_shift_register_length)); - return bit; + return output; + } + + unsigned char next_bit_scramble(unsigned char input) { + unsigned char output = d_shift_register & 1; + unsigned char newbit = (popCount( d_shift_register & d_mask )%2)^(input & 1); + d_shift_register = ((d_shift_register>>1) | (newbit<<d_shift_register_length)); + return output; + } + + unsigned char next_bit_descramble(unsigned char input) { + unsigned char output = (popCount( d_shift_register & d_mask )%2)^(input & 1); + unsigned char newbit = input & 1; + d_shift_register = ((d_shift_register>>1) | (newbit<<d_shift_register_length)); + return output; } + /*! * Rotate the register through x number of bits * where we are just throwing away the results to get queued up correctly |