convolutional.h

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// This file is part of LeanSDR Copyright (C) 2016-2018 <pabr@pabr.org>.
// See the toplevel README for more information.
//
// This program 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 of the License, or
// (at your option) any later version.
//
// This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

#ifndef LEANSDR_CONVOLUTIONAL_H
#define LEANSDR_CONVOLUTIONAL_H

#include "framework.h"
#include "sdr.h"

namespace leansdr
{

// ALGEBRAIC DECONVOLUTION

// QPSK 1/2 only.
// This is a straightforward implementation, provided for reference.
// deconvol_poly2 is functionally equivalent and much faster.

template <typename Tin,        // Input IQ symbols
          typename Thist,      // Input shift register (IQIQIQ...)
          Thist POLY_DECONVOL, // Taps (IQIQIQ...)
          Thist POLY_ERRORS>
struct deconvol_poly
{
    typedef u8 hardsymbol;

    // Support soft of float input
    inline u8 SYMVAL(const hardsymbol *s) { return *s; }
    inline u8 SYMVAL(const softsymbol *s) { return s->symbol; }

    typedef u8 decoded_byte;

    deconvol_poly() : hist(0) {}

    // Remap and deconvolve [nb*8] symbols into [nb] bytes.
    // Return estimated number of bit errors.

    int run(const Tin *pin, const u8 remap[], decoded_byte *pout, int nb)
    {
        int nerrors = 0;
        int halfway = nb / 2;

        for (; nb--; ++pout)
        {
            decoded_byte byte = 0;

            for (int bit = 8; bit--; ++pin)
            {
                hist = (hist << 2) | remap[SYMVAL(pin)];
                byte = (byte << 1) | parity(hist & POLY_DECONVOL);
                if (nb < halfway)
                    nerrors += parity(hist & POLY_ERRORS);
            }

            *pout = byte;
        }

        return nerrors;
    }

  private:
    Thist hist;

}; // deconvol_poly

// ALGEBRAIC DECONVOLUTION, OPTIMIZED

// QPSK 1/2 only.
// Functionally equivalent to deconvol_poly,
// but processing 32 bits in parallel.

template <typename Tin,   // Input IQ symbols
          typename Thist, // Input shift registers (one for I, one for Q)
          typename Tpoly, // Taps (interleaved IQIQIQ...)
          Tpoly POLY_DECONVOL,
          Tpoly POLY_ERRORS>
struct deconvol_poly2
{
    typedef u8 hardsymbol;

    // Support instanciation of template with soft of float input
    inline u8 SYMVAL(const hardsymbol *s) { return *s; }
    inline u8 SYMVAL(const softsymbol *s) { return s->symbol; }

    typedef u8 decoded_byte;

    deconvol_poly2() : inI(0), inQ(0) {}

    // Remap and deconvolve [nb*8] symbols into [nb] bytes.
    // Return estimated number of bit errors.

    int run(const Tin *pin, const u8 remap[], decoded_byte *pout, int nb)
    {
        if (nb & (sizeof(Thist) - 1)) {
            fail("Must deconvolve sizeof(Thist) bytes at a time");
        }

        nb /= sizeof(Thist);
        unsigned long nerrors = 0;
        int halfway = nb / 2;
        Thist histI = inI, histQ = inQ;

        for (; nb--;)
        {
            // This is where we convolve bits in parallel.
            Thist wd = 0; // decoded bits
            Thist we = 0; // error bits (should be 0)
#if 0
    // Trust gcc to unroll and evaluate the bit tests at compile-time.
    for ( int bit=sizeof(Thist)*8; bit--; ++pin ) {
      u8 iq = remap[SYMVAL(pin)];
      histI = (histI<<1) | (iq>>1);
      histQ = (histQ<<1) | (iq&1);
      if ( POLY_DECONVOL & ((Tpoly)2<<(2*bit)) ) wd ^= histI;
      if ( POLY_DECONVOL & ((Tpoly)1<<(2*bit)) ) wd ^= histQ;
      if ( POLY_ERRORS   & ((Tpoly)2<<(2*bit)) ) we ^= histI;
      if ( POLY_ERRORS   & ((Tpoly)1<<(2*bit)) ) we ^= histQ;
    }
#else
            // Unroll manually.
#define LOOP(bit)                                    \
    {                                                \
        u8 iq = remap[SYMVAL(pin)];                  \
        histI = (histI << 1) | (iq >> 1);            \
        histQ = (histQ << 1) | (iq & 1);             \
        if (POLY_DECONVOL & ((Tpoly)2 << (2 * bit))) \
            wd ^= histI;                             \
        if (POLY_DECONVOL & ((Tpoly)1 << (2 * bit))) \
            wd ^= histQ;                             \
        if (POLY_ERRORS & ((Tpoly)2 << (2 * bit)))   \
            we ^= histI;                             \
        if (POLY_ERRORS & ((Tpoly)1 << (2 * bit)))   \
            we ^= histQ;                             \
        ++pin;                                       \
    }
            // Don't shift by more than the operand width
            switch (sizeof(Thist) * 8)
            {
#if 0 // Not needed yet - avoid compiler warnings
    case 64:
      LOOP(63); LOOP(62); LOOP(61); LOOP(60);
      LOOP(59); LOOP(58); LOOP(57); LOOP(56);
      LOOP(55); LOOP(54); LOOP(53); LOOP(52);
      LOOP(51); LOOP(50); LOOP(49); LOOP(48);
      LOOP(47); LOOP(46); LOOP(45); LOOP(44);
      LOOP(43); LOOP(42); LOOP(41); LOOP(40);
      LOOP(39); LOOP(38); LOOP(37); LOOP(36);
      LOOP(35); LOOP(34); LOOP(33); LOOP(32);
      // Fall-through
#endif
            case 32:
                LOOP(31);
                LOOP(30);
                LOOP(29);
                LOOP(28);
                LOOP(27);
                LOOP(26);
                LOOP(25);
                LOOP(24);
                LOOP(23);
                LOOP(22);
                LOOP(21);
                LOOP(20);
                LOOP(19);
                LOOP(18);
                LOOP(17);
                LOOP(16);
                // Fall-through
            case 16:
                LOOP(15);
                LOOP(14);
                LOOP(13);
                LOOP(12);
                LOOP(11);
                LOOP(10);
                LOOP(9);
                LOOP(8);
                // Fall-through
            case 8:
                LOOP(7);
                LOOP(6);
                LOOP(5);
                LOOP(4);
                LOOP(3);
                LOOP(2);
                LOOP(1);
                LOOP(0);
                break;
            default:
                fail("Thist not supported");
            }
#undef LOOP
#endif
            switch (sizeof(Thist) * 8)
            {
#if 0 // Not needed yet - avoid compiler warnings
    case 64:
      *pout++ = wd >> 56;
      *pout++ = wd >> 48;
      *pout++ = wd >> 40;
      *pout++ = wd >> 32;
      // Fall-through
#endif
            case 32:
                *pout++ = wd >> 24;
                *pout++ = wd >> 16;
                // Fall-through
            case 16:
                *pout++ = wd >> 8;
                // Fall-through
            case 8:
                *pout++ = wd;
                break;
            default:
                fail("Thist not supported");
            }
            // Count errors when the shift registers are full
            if (nb < halfway)
                nerrors += hamming_weight(we);
        }

        inI = histI;
        inQ = histQ;
        return nerrors;
    }

  private:
    Thist inI, inQ;
}; // deconvol_poly2

// CONVOLUTIONAL ENCODER

// QPSK 1/2 only.

template <typename Thist, uint64_t POLY1, uint64_t POLY2>
struct convol_poly2
{
    typedef u8 uncoded_byte;
    typedef u8 hardsymbol;

    convol_poly2() : hist(0) {}

    // Convolve [count] bytes into [count*8] symbols, and remap.

    void run(const uncoded_byte *pin, const u8 remap[],
             hardsymbol *pout, int count)
    {
        for (; count--; ++pin)
        {
            uncoded_byte b = *pin;

            for (int bit = 8; bit--; ++pout)
            {
                hist = (hist >> 1) | (((b >> bit) & 1) << 6);
                u8 s = (parity(hist & POLY1) << 1) | parity(hist & POLY2);
                *pout = remap[s];
            }
        }
    }

  private:
    Thist hist;
}; // convol_poly2

// Generic BPSK..256QAM and puncturing

template <typename Thist, int HISTSIZE>
struct convol_multipoly
{
    typedef u8 uncoded_byte;
    typedef u8 hardsymbol;
    int bits_in, bits_out, bps;
    const Thist *polys; // [bits_out]

    convol_multipoly()
        : bits_in(0), bits_out(0), bps(0),
          hist(0), nhist(0), sersymb(0), nsersymb(0)
    {
    }

    void encode(const uncoded_byte *pin, hardsymbol *pout, int count)
    {
        if (!bits_in || !bits_out || !bps) {
            fatal("convol_multipoly not configured");
        }

        hardsymbol symbmask = (1 << bps) - 1;

        for (; count--; ++pin)
        {
            uncoded_byte b = *pin;

            for (int bit = 8; bit--;)
            {
                hist = (hist >> 1) | ((Thist)((b >> bit) & 1) << (HISTSIZE - 1));
                ++nhist;

                if (nhist == bits_in)
                {
                    for (int p = 0; p < bits_out; ++p)
                    {
                        int b = parity((Thist)(hist & polys[p]));
                        sersymb = (sersymb << 1) | b;
                    }

                    nhist = 0;
                    nsersymb += bits_out;

                    while (nsersymb >= bps)
                    {
                        hardsymbol s = (sersymb >> (nsersymb - bps)) & symbmask;
                        *pout++ = s;
                        nsersymb -= bps;
                    }
                }
            }
        }
        // Ensure deterministic output size
        // TBD We can relax this
        if (nhist || nsersymb) {
            fatal("partial run");
        }
    }

  private:
    Thist hist;
    int nhist;
    Thist sersymb;
    int nsersymb;
}; // convol_multipoly

} // namespace leansdr

#endif // LEANSDR_CONVOLUTIONAL_H