subroutine ft8b(dd0,newdat,nQSOProgress,nfqso,nftx,ndepth,lapon,lapcqonly, &
      napwid,nagain,iaptype,f1,xdt,xbase,apsym,nharderrors,dmin,      &
      nbadcrc,ipass,msgcall,msggrid,xsnr)

  use crc
  include 'ft8_params.f90'
  parameter(NP2=2812)
  character msgcall*12,msggrid*4,message*22
  real a(5)
  real s1(0:7,ND),s2(0:7,NN),s1sort(8*ND)
  real ps(0:7),psl(0:7)
  real bmeta(3*ND),bmetb(3*ND),bmetap(3*ND)
  real llr(3*ND),llra(3*ND),llr0(3*ND),llr1(3*ND),llrap(3*ND)           !Soft symbols
  complex dd0(NMAX)
  integer*1 decoded(KK),apmask(3*ND),cw(3*ND)
  integer apsym(KK)
  integer mcq(28),mde(28),mrrr(16),m73(16),mrr73(16)
  integer itone(NN)
  integer indxs1(8*ND)
  integer icos7(0:6),ip(1)
  integer nappasses(0:5)  !Number of decoding passes to use for each QSO state
  integer naptypes(0:5,4) ! (nQSOProgress, decoding pass)  maximum of 4 passes for now
  complex cd0(3200)
  complex ctwk(32)
  complex csymb(32)
  logical first,newdat,lapon,lapcqonly,nagain
  equivalence (s1,s1sort)
  data icos7/2,5,6,0,4,1,3/
  data mcq/1,1,1,1,1,0,1,0,0,0,0,0,1,0,0,0,0,0,1,1,0,0,0,1,1,0,0,1/
  data mrrr/0,1,1,1,1,1,1,0,1,1,0,0,1,1,1,1/
  data m73/0,1,1,1,1,1,1,0,1,1,0,1,0,0,0,0/
  data mde/1,1,1,1,1,1,1,1,0,1,1,0,0,1,0,0,0,0,0,1,1,1,0,1,0,0,0,1/
  data mrr73/0,0,0,0,0,0,1,0,0,0,0,1,0,1,0,1/
  data first/.true./
  save nappasses,naptypes

  if(first) then
     mcq=2*mcq-1
     mde=2*mde-1
     mrrr=2*mrrr-1
     m73=2*m73-1
     mrr73=2*mrr73-1
     nappasses(0)=2
     nappasses(1)=2
     nappasses(2)=2
     nappasses(3)=4
     nappasses(4)=4
     nappasses(5)=3

! iaptype
!------------------------
!   1        CQ     ???    ???
!   2        MyCall ???    ???
!   3        MyCall DxCall ???
!   4        MyCall DxCall RRR
!   5        MyCall DxCall 73
!   6        MyCall DxCall RR73
!   7        ???    DxCall ???

     naptypes(0,1:4)=(/1,2,0,0/)
     naptypes(1,1:4)=(/2,3,0,0/)
     naptypes(2,1:4)=(/2,3,0,0/)
     naptypes(3,1:4)=(/3,4,5,6/)
     naptypes(4,1:4)=(/3,4,5,6/)
     naptypes(5,1:4)=(/3,1,2,0/)
     first=.false.
  endif

  max_iterations=30
  nharderrors=-1
  fs2=4000.0/NDOWN
  dt2=1.0/fs2
  twopi=8.0*atan(1.0)
  delfbest=0.
  ibest=0

  call ft8_downsample(dd0,newdat,f1,cd0)   !Mix f1 to baseband and downsample

  i0=nint((xdt+0.5)*fs2)                   !Initial guess for start of signal
  smax=0.0
  do idt=i0-8,i0+8                         !Search over +/- one quarter symbol
     call sync8d(cd0,idt,ctwk,0,sync)
     if(sync.gt.smax) then
        smax=sync
        ibest=idt
     endif
  enddo
  xdt2=ibest*dt2                           !Improved estimate for DT

! Now peak up in frequency
  i0=nint(xdt2*fs2)
  smax=0.0
  do ifr=-5,5                              !Search over +/- 2.5 Hz
    delf=ifr*0.5
    dphi=twopi*delf*dt2
    phi=0.0
    do i=1,32
      ctwk(i)=cmplx(cos(phi),sin(phi))
      phi=mod(phi+dphi,twopi)
    enddo
   call sync8d(cd0,i0,ctwk,1,sync)
    if( sync .gt. smax ) then
      smax=sync
      delfbest=delf
    endif
  enddo
  a=0.0
  a(1)=-delfbest
  call twkfreq1(cd0,NP2,fs2,a,cd0)
  xdt=xdt2
  f1=f1+delfbest                           !Improved estimate of DF

  call sync8d(cd0,i0,ctwk,2,sync)

  j=0
  do k=1,NN
    i1=ibest+(k-1)*32
    csymb=cmplx(0.0,0.0)
    if( i1.ge.1 .and. i1+31 .le. NP2 ) csymb=cd0(i1:i1+31)
    call four2a(csymb,32,1,-1,1)
    s2(0:7,k)=abs(csymb(1:8))/1e3
  enddo

! sync quality check
  is1=0
  is2=0
  is3=0
  do k=1,7
    ip=maxloc(s2(:,k))
    if(icos7(k-1).eq.(ip(1)-1)) is1=is1+1
    ip=maxloc(s2(:,k+36))
    if(icos7(k-1).eq.(ip(1)-1)) is2=is2+1
    ip=maxloc(s2(:,k+72))
    if(icos7(k-1).eq.(ip(1)-1)) is3=is3+1
  enddo
! hard sync sum - max is 21
  nsync=is1+is2+is3
  if(nsync .le. 6) then ! bail out
    nbadcrc=1
    return
  endif

  j=0
  do k=1,NN
     if(k.le.7) cycle
     if(k.ge.37 .and. k.le.43) cycle
     if(k.gt.72) cycle
     j=j+1
     s1(0:7,j)=s2(0:7,k)
  enddo

  call indexx(s1sort,8*ND,indxs1)
  xmeds1=s1sort(indxs1(nint(0.5*8*ND)))
  s1=s1/xmeds1

  do j=1,ND
     i4=3*j-2
     i2=3*j-1
     i1=3*j
! Max amplitude
     ps=s1(0:7,j)
     r1=max(ps(1),ps(3),ps(5),ps(7))-max(ps(0),ps(2),ps(4),ps(6))
     r2=max(ps(2),ps(3),ps(6),ps(7))-max(ps(0),ps(1),ps(4),ps(5))
     r4=max(ps(4),ps(5),ps(6),ps(7))-max(ps(0),ps(1),ps(2),ps(3))
     bmeta(i4)=r4
     bmeta(i2)=r2
     bmeta(i1)=r1
     bmetap(i4)=r4
     bmetap(i2)=r2
     bmetap(i1)=r1
! Max log metric
     psl=log(ps)
     r1=max(psl(1),psl(3),psl(5),psl(7))-max(psl(0),psl(2),psl(4),psl(6))
     r2=max(psl(2),psl(3),psl(6),psl(7))-max(psl(0),psl(1),psl(4),psl(5))
     r4=max(psl(4),psl(5),psl(6),psl(7))-max(psl(0),psl(1),psl(2),psl(3))
     bmetb(i4)=r4
     bmetb(i2)=r2
     bmetb(i1)=r1

! Metric for Cauchy noise
!     r1=log(ps(1)**3+ps(3)**3+ps(5)**3+ps(7)**3)- &
!        log(ps(0)**3+ps(2)**3+ps(4)**3+ps(6)**3)
!     r2=log(ps(2)**3+ps(3)**3+ps(6)**3+ps(7)**3)- &
!        log(ps(0)**3+ps(1)**3+ps(4)**3+ps(5)**3)
!     r4=log(ps(4)**3+ps(5)**3+ps(6)**3+ps(7)**3)- &
!        log(ps(0)**3+ps(1)**3+ps(2)**3+ps(3)**3)
! Metric for AWGN, no fading
!     bscale=2.5
!     b0=bessi0(bscale*ps(0))
!     b1=bessi0(bscale*ps(1))
!     b2=bessi0(bscale*ps(2))
!     b3=bessi0(bscale*ps(3))
!     b4=bessi0(bscale*ps(4))
!     b5=bessi0(bscale*ps(5))
!     b6=bessi0(bscale*ps(6))
!     b7=bessi0(bscale*ps(7))
!     r1=log(b1+b3+b5+b7)-log(b0+b2+b4+b6)
!     r2=log(b2+b3+b6+b7)-log(b0+b1+b4+b5)
!     r4=log(b4+b5+b6+b7)-log(b0+b1+b2+b3)

     if(nQSOProgress .eq. 0 .or. nQSOProgress .eq. 5) then
! When bits 88:115 are set as ap bits, bit 115 lives in symbol 39 along
! with no-ap bits 116 and 117. Take care of metrics for bits 116 and 117.
        if(j.eq.39) then  ! take care of bits that live in symbol 39
           if(apsym(28).lt.0) then
              bmetap(i2)=max(ps(2),ps(3))-max(ps(0),ps(1))
              bmetap(i1)=max(ps(1),ps(3))-max(ps(0),ps(2))
           else
              bmetap(i2)=max(ps(6),ps(7))-max(ps(4),ps(5))
              bmetap(i1)=max(ps(5),ps(7))-max(ps(4),ps(6))
           endif
        endif
     endif

! When bits 116:143 are set as ap bits, bit 115 lives in symbol 39 along
! with ap bits 116 and 117. Take care of metric for bit 115.
!        if(j.eq.39) then  ! take care of bit 115
!           iii=2*(apsym(29)+1)/2 + (apsym(30)+1)/2  ! known values of bits 116 & 117
!           if(iii.eq.0) bmetap(i4)=ps(4)-ps(0)
!           if(iii.eq.1) bmetap(i4)=ps(5)-ps(1)
!           if(iii.eq.2) bmetap(i4)=ps(6)-ps(2)
!           if(iii.eq.3) bmetap(i4)=ps(7)-ps(3)
!        endif

! bit 144 lives in symbol 48 and will be 1 if it is set as an ap bit.
! take care of metrics for bits 142 and 143
     if(j.eq.48) then  ! bit 144 is always 1
       bmetap(i4)=max(ps(5),ps(7))-max(ps(1),ps(3))
       bmetap(i2)=max(ps(3),ps(7))-max(ps(1),ps(5))
     endif

! bit 154 lives in symbol 52 and will be 0 if it is set as an ap bit
! take care of metrics for bits 155 and 156
     if(j.eq.52) then  ! bit 154 will be 0 if it is set as an ap bit.
        bmetap(i2)=max(ps(2),ps(3))-max(ps(0),ps(1))
        bmetap(i1)=max(ps(1),ps(3))-max(ps(0),ps(2))
     endif

  enddo

  call normalizebmet(bmeta,3*ND)
  call normalizebmet(bmetb,3*ND)
  call normalizebmet(bmetap,3*ND)

  scalefac=2.83
  llr0=scalefac*bmeta
  llr1=scalefac*bmetb
  llra=scalefac*bmetap  ! llr's for use with ap
  apmag=scalefac*(maxval(abs(bmetap))*1.01)

! pass #
!------------------------------
!   1        regular decoding
!   2        erase 24
!   3        erase 48
!   4        ap pass 1
!   5        ap pass 2
!   6        ap pass 3
!   7        ap pass 4, etc.

  if(lapon) then
     if(.not.lapcqonly) then
        npasses=4+nappasses(nQSOProgress)
     else
        npasses=5
     endif
  else
     npasses=4
  endif

  do ipass=1,npasses

     llr=llr0
     if(ipass.eq.2) llr=llr1
     if(ipass.eq.3) llr(1:24)=0.
     if(ipass.eq.4) llr(1:48)=0.
     if(ipass.le.4) then
        apmask=0
        llrap=llr
        iaptype=0
     endif

     if(ipass .gt. 4) then
        if(.not.lapcqonly) then
           iaptype=naptypes(nQSOProgress,ipass-4)
        else
           iaptype=1
        endif
        if(iaptype.ge.3 .and. (abs(f1-nfqso).gt.napwid .and. abs(f1-nftx).gt.napwid) ) cycle
        if(iaptype.eq.1 .or. iaptype.eq.2 ) then ! AP,???,???
           apmask=0
           apmask(88:115)=1    ! first 28 bits are AP
           apmask(144)=1       ! not free text
           llrap=llr
           if(iaptype.eq.1) llrap(88:115)=apmag*mcq
           if(iaptype.eq.2) llrap(88:115)=apmag*apsym(1:28)
           llrap(116:117)=llra(116:117)
           llrap(142:143)=llra(142:143)
           llrap(144)=-apmag
        endif
        if(iaptype.eq.3) then   ! mycall, dxcall, ???
           apmask=0
           apmask(88:115)=1   ! mycall
           apmask(116:143)=1  ! hiscall
           apmask(144)=1      ! not free text
           llrap=llr
           llrap(88:143)=apmag*apsym(1:56)
           llrap(144)=-apmag
        endif
        if(iaptype.eq.4 .or. iaptype.eq.5 .or. iaptype.eq.6) then
           apmask=0
           apmask(88:115)=1   ! mycall
           apmask(116:143)=1  ! hiscall
           apmask(144:159)=1  ! RRR or 73 or RR73
           llrap=llr
           llrap(88:143)=apmag*apsym(1:56)
           if(iaptype.eq.4) llrap(144:159)=apmag*mrrr
           if(iaptype.eq.5) llrap(144:159)=apmag*m73
           if(iaptype.eq.6) llrap(144:159)=apmag*mrr73
        endif
        if(iaptype.eq.7) then   ! ???, dxcall, ???
           apmask=0
           apmask(116:143)=1  ! hiscall
           apmask(144)=1      ! not free text
           llrap=llr
           llrap(115)=llra(115)
           llrap(116:143)=apmag*apsym(29:56)
           llrap(144)=-apmag
        endif
     endif

     cw=0
     call bpdecode174(llrap,apmask,max_iterations,decoded,cw,nharderrors,  &
          niterations)
     dmin=0.0
     if(ndepth.eq.3 .and. nharderrors.lt.0) then
        ndeep=3
        if(abs(nfqso-f1).le.napwid .or. abs(nftx-f1).le.napwid) then
          if((ipass.eq.3 .or. ipass.eq.4) .and. .not.nagain) then
            ndeep=3
          else
            ndeep=4
          endif
        endif
        if(nagain) ndeep=5
        call osd174(llrap,apmask,ndeep,decoded,cw,nharderrors,dmin)
     endif
     nbadcrc=1
     message='                      '
     xsnr=-99.0
     if(count(cw.eq.0).eq.174) cycle           !Reject the all-zero codeword
     if(nharderrors.ge.0 .and. nharderrors+dmin.lt.60.0 .and. &
        .not.(sync.lt.2.0 .and. nharderrors.gt.35)      .and. &
        .not.(ipass.gt.2 .and. nharderrors.gt.39)       .and. &
        .not.(ipass.eq.4 .and. nharderrors.gt.30)             &
       ) then
        call chkcrc12a(decoded,nbadcrc)
     else
        nharderrors=-1
        cycle
     endif
     if(nbadcrc.eq.0) then
        call extractmessage174(decoded,message,msgcall,msggrid,ncrcflag)
        call genft8(message,0,itone)
        xsig=0.0
        xnoi=0.0
        do i=1,79
           xsig=xsig+s2(itone(i),i)**2
           ios=mod(itone(i)+4,7)
           xnoi=xnoi+s2(ios,i)**2
        enddo
        xsnr=0.001
        if(xnoi.gt.0 .and. xnoi.lt.xsig) xsnr=xsig/xnoi-1.0
        xsnr=10.0*log10(xsnr)-27.0
        xsnr2=db(xsig/xbase - 1.0) - 32.0
        if(.not.nagain) xsnr=xsnr2
        if(xsnr .lt. -24.0) xsnr=-24.0
        return
     endif
  enddo

  return
end subroutine ft8b

subroutine normalizebmet(bmet,n)
  real bmet(n)

  bmetav=sum(bmet)/real(n)
  bmet2av=sum(bmet*bmet)/real(n)
  var=bmet2av-bmetav*bmetav
  if( var .gt. 0.0 ) then
     bmetsig=sqrt(var)
  else
     bmetsig=sqrt(bmet2av)
  endif
  bmet=bmet/bmetsig
  return
end subroutine normalizebmet


function bessi0(x)
! From Numerical Recipes
   real bessi0,x
   double precision p1,p2,p3,p4,p5,p6,p7,q1,q2,q3,q4,q5,q6,q7,q8,q9,y
   save p1,p2,p3,p4,p5,p6,p7,q1,q2,q3,q4,q5,q6,q7,q8,q9
   data p1,p2,p3,p4,p5,p6,p7/1.0d0,3.5156229d0,3.0899424d0,1.2067492d0, &
      0.2659732d0,0.360768d-1,0.45813d-2/
   data q1,q2,q3,q4,q5,q6,q7,q8,q9/0.39894228d0,0.1328592d-1,           &
      0.225319d-2,-0.157565d-2,0.916281d-2,-0.2057706d-1,               &
      0.2635537d-1,-0.1647633d-1,0.392377d-2/

   if (abs(x).lt.3.75) then
      y=(x/3.75)**2
      bessi0=p1+y*(p2+y*(p3+y*(p4+y*(p5+y*(p6+y*p7)))))
   else
      ax=abs(x)
      y=3.75/ax
      bessi0=(exp(ax)/sqrt(ax))*(q1+y*(q2+y*(q3+y*(q4         &
           +y*(q5+y*(q6+y*(q7+y*(q8+y*q9))))))))
   endif
   return
end function bessi0