diff options
| author | Daniel Estévez <daniel@destevez.net> | 2021-06-06 11:25:57 +0200 |
|---|---|---|
| committer | mormj <34754695+mormj@users.noreply.github.com> | 2021-06-12 12:01:12 -0400 |
| commit | 51c504ebb1ca21c5f7071826c1af03e45e391a65 (patch) | |
| tree | dbabf0b0b825f834cff2067248d193fe8d951dd8 /gr-digital/lib/diff_decoder_bb_impl.cc | |
| parent | 16d1b0215d59c52009b09867fbfce0b4c3585add (diff) | |
digital: Add NRZI option to differential en/decoder
This adds an option to the differential encoder an decoder blocks
to perform NRZI encoding and decoding. NRZI only makes sense with
a modulus of 2, so the blocks constructors will throw and exception
if passed nrzi = true and a modulus different from 2.
The GRC blocks handle this by hiding the modulus field if the user
selects NRZI encoding.
A new unit test for the NRZI version of the blocks is added. Besides
checking that encode plus decode gives the original, this test also
compares the C++ implementation results against a Numpy implementation.
Additionally, a faster implementation of differential encoding/
decoding for modulus 2 is included here.
Signed-off-by: Daniel Estévez <daniel@destevez.net>
Diffstat (limited to 'gr-digital/lib/diff_decoder_bb_impl.cc')
| -rw-r--r-- | gr-digital/lib/diff_decoder_bb_impl.cc | 33 |
1 files changed, 27 insertions, 6 deletions
diff --git a/gr-digital/lib/diff_decoder_bb_impl.cc b/gr-digital/lib/diff_decoder_bb_impl.cc index 95e5c2e9c3..f9b093400d 100644 --- a/gr-digital/lib/diff_decoder_bb_impl.cc +++ b/gr-digital/lib/diff_decoder_bb_impl.cc @@ -1,6 +1,7 @@ /* -*- c++ -*- */ /* * Copyright 2006,2010,2012 Free Software Foundation, Inc. + * Copyright 2021 Daniel Estevez <daniel@destevez.net> * * This file is part of GNU Radio * @@ -15,19 +16,27 @@ #include "diff_decoder_bb_impl.h" #include <gnuradio/io_signature.h> +#include <stdexcept> + namespace gr { namespace digital { -diff_decoder_bb::sptr diff_decoder_bb::make(unsigned int modulus) +diff_decoder_bb::sptr diff_decoder_bb::make(unsigned int modulus, + enum diff_coding_type coding) { - return gnuradio::make_block_sptr<diff_decoder_bb_impl>(modulus); + return gnuradio::make_block_sptr<diff_decoder_bb_impl>(modulus, coding); } -diff_decoder_bb_impl::diff_decoder_bb_impl(unsigned int modulus) +diff_decoder_bb_impl::diff_decoder_bb_impl(unsigned int modulus, + enum diff_coding_type coding) : sync_block("diff_decoder_bb", io_signature::make(1, 1, sizeof(unsigned char)), io_signature::make(1, 1, sizeof(unsigned char))), - d_modulus(modulus) + d_modulus(modulus), + d_coding(coding) { + if (d_coding == DIFF_NRZI && d_modulus != 2) { + throw std::runtime_error("diff_decoder: NRZI only supported with modulus 2"); + } set_history(2); // need to look at two inputs } @@ -43,8 +52,20 @@ int diff_decoder_bb_impl::work(int noutput_items, unsigned modulus = d_modulus; - for (int i = 0; i < noutput_items; i++) { - out[i] = (in[i] - in[i - 1]) % modulus; + if (d_coding == DIFF_NRZI) { + for (int i = 0; i < noutput_items; i++) { + out[i] = ~(in[i] ^ in[i - 1]) & 1; + } + } else if (modulus == 2) { + // optimized implementation for modulus 2 + for (int i = 0; i < noutput_items; i++) { + out[i] = (in[i] ^ in[i - 1]) & 1; + } + } else { + // implementation for modulus != 2 + for (int i = 0; i < noutput_items; i++) { + out[i] = (in[i] - in[i - 1]) % modulus; + } } return noutput_items; |