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/* -*- c++ -*- */
/*
* Copyright 2002,2006 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3, or (at your option)
* any later version.
*
* GNU Radio is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#include <gnuradio/atsc/sliding_correlator_impl.h>
#include <gnuradio/atsc/pnXXX_impl.h>
// #define TRY_BACKWARDS
/*
* Return the number of 1's in v.
* This magic code is explained wonderfully in the AMD Athlon
* optimization guide, pg 136.
*/
static inline int popcount32 (unsigned long v)
{
unsigned long w = v - ((v >> 1) & 0x55555555);
unsigned long x = (w & 0x33333333) + ((w >> 2) & 0x33333333);
unsigned long y = (x + (x >> 4)) & 0x0f0f0f0f;
unsigned long z = (y * 0x01010101) >> 24;
return z;
}
atsci_sliding_correlator::atsci_sliding_correlator ()
{
#if defined(TRY_BACKWARDS)
for (int i = 511 - 1; i >= 0; i--)
mask.shift_in (atsc_pn511[i]);
#else
for (unsigned i = 0; i < 511; i++)
mask.shift_in (atsc_pn511[i]);
#endif
and_mask.shift_in (0);
for (int i = 0; i < 511; i++)
and_mask.shift_in (1);
}
/*
* we shift in from the top of the register towards the bottom
*
* +-- bits enter here...
* |
* v
* block 0 | block 1 | block 2 ... | block N-1
* |
* +--> ... and drop out here
*
*/
inline void
atsci_sliding_correlator::shift_reg::shift_in (int bit)
{
for (int i = NSRBLOCKS - 1; i > 0; i--)
d[i] = ((d[i-1] & 0x1) << (srblock_bitsize - 1)) | (d[i] >> 1);
d[0] = (((srblock) bit) << (srblock_bitsize - 1)) | (d[0] >> 1);
}
int
atsci_sliding_correlator::input_bit (int bit)
{
input.shift_in (bit);
// can probably get a win by unrolling the loop, if we need to.
int count = 0;
for (int i = 0; i < NSRBLOCKS; i++)
count += popcount32 ((input.d[i] ^ mask.d[i]) & and_mask.d[i]);
return count;
}
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