sdrangel/plugins/channelrx/demoddatv/leansdr/convolutional.h

#ifndef LEANSDR_CONVOLUTIONAL_H
#define LEANSDR_CONVOLUTIONAL_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

#endif  // LEANSDR_CONVOLUTIONAL_H