FT4: Imrovements to sync.

Divide DT search range into 3 segments. Search central segment (near DT=0)
first and try to decode the largest peak. Then find the largest peak in each
of the surrounding segments and try to decode those only if the peak is larger
than the one found in the central segment.

Also re-indent ft4_decode.f90 and some other minor tweaks.

lib/ft4/getcandidates4.f90

@@ -8,7 +8,7 @@ subroutine getcandidates4(dd,fa,fb,syncmin,nfqso,maxcand,savg,candidate,   &
   real x(NFFT1)
   real window(NFFT1)
   complex cx(0:NH1)
-  real candidate(3,maxcand)
+  real candidate(2,maxcand)
   real dd(NMAX)
   integer ipk(1)
   equivalence (x,cx)
@@ -64,8 +64,7 @@ subroutine getcandidates4(dd,fa,fb,syncmin,nfqso,maxcand,savg,candidate,   &
         speak=savsm(i) - 0.25*(savsm(i-1)-savsm(i+1))*del
         ncand=ncand+1
         candidate(1,ncand)=fpeak
-        candidate(2,ncand)=-99.99
+        candidate(2,ncand)=speak
-        candidate(3,ncand)=speak
         if(ncand.eq.maxcand) exit
      endif
   enddo

lib/ft4/sync4d.f90

@@ -18,7 +18,7 @@ subroutine sync4d(cd0,i0,ctwk,itwk,sync)
   data first/.true./
   save first,twopi,csynca,csyncb,csyncc,csyncd,fac
 
-  p(z1)=sqrt(real(z1*fac)**2 + aimag(z1*fac)**2)          !Statement function for power
+  p(z1)=(real(z1*fac)**2 + aimag(z1*fac)**2)**0.5          !Statement function for power
 
   if( first ) then
     twopi=8.0*atan(1.0)

lib/ft4_decode.f90

@@ -50,7 +50,7 @@ contains
       real bitmetrics(2*NN,3)
       real dd(NMAX)
       real llr(2*ND),llra(2*ND),llrb(2*ND),llrc(2*ND),llrd(2*ND)
-      real candidate(3,100)
+      real candidate(2,100)
       real savg(NH1),sbase(NH1)
 
       integer apbits(2*ND)
@@ -229,7 +229,7 @@ contains
          dobigfft=.true.
          do icand=1,ncand
             f0=candidate(1,icand)
-            snr=candidate(3,icand)-1.0
+            snr=candidate(2,icand)-1.0
             call timer('ft4_down',0)
             call ft4_downsample(dd,dobigfft,f0,cd2)  !Downsample to 32 Sam/Sym
             call timer('ft4_down',1)
@@ -237,6 +237,7 @@ contains
             sum2=sum(cd2*conjg(cd2))/(real(NMAX)/real(NDOWN))
             if(sum2.gt.0.0) cd2=cd2/sqrt(sum2)
 ! Sample rate is now 12000/18 = 666.67 samples/second
+            do iseg=1,3                ! DT search is done over 3 segments
                do isync=1,2          
                   if(isync.eq.1) then
                      idfmin=-12
@@ -244,6 +245,17 @@ contains
                      idfstp=3
                      ibmin=-344
                      ibmax=1012
+                     if(iseg.eq.1) then
+                        ibmin=108
+                        ibmax=560
+                     elseif(iseg.eq.2) then
+                        smax1=smax
+                        ibmin=560
+                        ibmax=1012
+                     elseif(iseg.eq.3) then
+                        ibmin=-344
+                        ibmax=108
+                     endif
                      ibstp=4
                   else
                      idfmin=idfbest-4
@@ -254,8 +266,8 @@ contains
                      ibstp=1
                   endif
                   ibest=-1
-               smax=-99.
                   idfbest=0
+                  smax=-99.
                   call timer('sync4d  ',0)
                   do idf=idfmin,idfmax,idfstp
                      do istart=ibmin,ibmax,ibstp
@@ -269,11 +281,13 @@ contains
                   enddo
                   call timer('sync4d  ',1)
                enddo
+               if(iseg.eq.1) smax1=smax
                if(smax.lt.0.7) cycle
-            f0=f0+real(idfbest)
+               if(iseg.gt.1 .and. smax.lt.smax1) cycle 
-            if( f0.le.10.0 .or. f0.ge.4990.0 ) cycle
+               f1=f0+real(idfbest)
+               if( f1.le.10.0 .or. f1.ge.4990.0 ) cycle
                call timer('ft4down ',0)
-            call ft4_downsample(dd,dobigfft,f0,cb) !Final downsample, corrected f0
+               call ft4_downsample(dd,dobigfft,f1,cb) !Final downsample, corrected f0
                call timer('ft4down ',1)
                sum2=sum(abs(cb)**2)/(real(NSS)*NN)
                if(sum2.gt.0.0) cb=cb/sqrt(sum2)
@@ -341,7 +355,7 @@ contains
 !
 ! Conditions that cause us to bail out of AP decoding
                      napwid=50
-                  if(ncontest.le.4 .and. iaptype.ge.3 .and. (abs(f0-nfqso).gt.napwid) ) cycle
+                     if(ncontest.le.4 .and. iaptype.ge.3 .and. (abs(f1-nfqso).gt.napwid) ) cycle
                      if(iaptype.ge.2 .and. apbits(1).gt.1) cycle  ! No, or nonstandard, mycall
                      if(iaptype.ge.3 .and. apbits(30).gt.1) cycle ! No, or nonstandard, dxcall
 
@@ -403,9 +417,9 @@ contains
 
                   if(doosd .and. nharderror.lt.0) then
                      ndeep=3
-                  if(abs(nfqso-f0).le.napwid) then
+!                  if(abs(nfqso-f1).le.napwid) then
-                     ndeep=4
+!                     ndeep=4
-                  endif
+!                  endif
                      call timer('osd174_91 ',0)
                      call osd174_91(llr,apmask,ndeep,message77,cw,nharderror,dmin)
                      call timer('osd174_91 ',1)
@@ -420,7 +434,7 @@ contains
                         call get_ft4_tones_from_77bits(message77,i4tone)
                         dt=real(ibest)/666.67
                         call timer('subtract',0)
-                     call subtractft4(dd,i4tone,f0,dt)
+                        call subtractft4(dd,i4tone,f1,dt)
                         call timer('subtract',1)
                      endif
                      idupe=0
@@ -437,12 +451,14 @@ contains
                      endif
                      nsnr=nint(max(-21.0,xsnr))
                      xdt=ibest/666.67 - 0.5
-!write(21,'(i6.6,i5,2x,f4.1,i6,2x,a37,2x,f4.1,3i3,f5.1,i4,i4)') & 
+!write(21,'(i6.6,i5,2x,f4.1,i6,2x,a37,2x,f4.1,3i3,f5.1,i4,i4,i4)') &
-!  nutc,nsnr,xdt,nint(f0),message,sync,iaptype,ipass,isp,dmin,nsync_qual,nharderror
+!  nutc,nsnr,xdt,nint(f1),message,smax,iaptype,ipass,isp,dmin,nsync_qual,nharderror,iseg
-                  call this%callback(sync,nsnr,xdt,f0,message,iaptype,qual)
+                     call this%callback(smax,nsnr,xdt,f1,message,iaptype,qual)
                      exit
                   endif
                enddo !Sequence estimation
+               if(nharderror.ge.0) exit
+            enddo !3 DT segments
          enddo    !Candidate list
       enddo       !Subtraction loop
       return