WSJT-X/lib/extract.f90

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Fortran
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subroutine extract(s3,nadd,nqd,ntrials,naggressive,ndepth,nexp_decode, &
ncount,nhist,decoded,ltext,nsf)
! Input:
! s3 64-point spectra for each of 63 data symbols
! nadd number of spectra summed into s3
! nqd 0/1 to indicate decode attempt at QSO frequency
! Output:
! ncount number of symbols requiring correction (-1 for no KV decode)
! nhist maximum number of identical symbol values
! decoded decoded message (if ncount >=0)
! ltext true if decoded message is free text
! nsf 0=no decode; 1=BM decode; 2=KV decode
use prog_args !shm_key, exe_dir, data_dir
use packjt
real s3(64,63)
character decoded*22
integer dat4(12)
integer mrsym(63),mr2sym(63),mrprob(63),mr2prob(63)
integer correct(63),tmp(63)
integer param(0:7)
integer indx(0:62)
real*8 tt
logical nokv,ltext
common/chansyms65/correct
data nokv/.false./,nsec1/0/
save
nbirdie=20
npct=50
afac1=1.1
nsf=0
nfail=0
decoded=' '
call pctile(s3,4032,npct,base)
s3=s3/base
! Get most reliable and second-most-reliable symbol values, and their
! probabilities
1 call demod64a(s3,nadd,afac1,mrsym,mrprob,mr2sym,mr2prob,ntest,nlow)
call chkhist(mrsym,nhist,ipk) !Test for birdies and QRM
if(nhist.ge.nbirdie) then
nfail=nfail+1
call pctile(s3,4032,npct,base)
s3(ipk,1:63)=base
if(nfail.gt.30) then
decoded=' '
ncount=-1
go to 900
endif
go to 1
endif
call graycode65(mrsym,63,-1) !Remove gray code
call interleave63(mrsym,-1) !Remove interleaving
call interleave63(mrprob,-1)
call graycode65(mr2sym,63,-1) !Remove gray code and interleaving
call interleave63(mr2sym,-1) !from second-most-reliable symbols
call interleave63(mr2prob,-1)
ntry=0
nverbose=0
call timer('sfrsd ',0)
call sfrsd2(mrsym,mrprob,mr2sym,mr2prob,ntrials,nverbose,correct, &
param,indx,tt,ntry)
call timer('sfrsd ',1)
ncandidates=param(0)
nhard=param(1)
nsoft=param(2)
if(nhard.lt.0 .and. ndepth.ge.5) then
call timer('exp_deco',0)
call exp_decode65(mrsym,mrprob,mr2sym,nexp_decode,nhard,nsoft,nbest, &
correct)
if(nbest.gt.72+2*naggressive) then
nhard=-1
endif
call timer('exp_deco',1)
endif
ndone=ndone+1
ncount=-1
decoded=' '
ltext=.false.
if(nhard.ge.0) then
!turn the corrected symbol array into channel symbols for subtraction
!pass it back to jt65a via common block "chansyms65"
do i=1,12
dat4(i)=correct(13-i)
enddo
do i=1,63
tmp(i)=correct(64-i)
enddo
correct(1:63)=tmp(1:63)
call interleave63(correct,63,1)
call graycode65(correct,63,1)
call unpackmsg(dat4,decoded) !Unpack the user message
ncount=0
if(iand(dat4(10),8).ne.0) ltext=.true.
nsf=1
endif
900 continue
return
end subroutine extract