WSJT-X/lib/peakdt9.f90

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Fortran
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subroutine peakdt9(c0,npts8,nsps8,istart,foffset,idtpk)
complex c0(0:npts8-1)
complex zsum
include 'jt9sync.f90'
twopi=8.0*atan(1.0)
smax=0.
f0=foffset
dphi=twopi*f0/1500.0
do idt=-5,5
i0=istart + 0.0625*nsps8*idt
sum=0.
do j=1,16
i1=(ii(j)-1)*nsps8 + i0
phi=0.
zsum=0.
do i=i1,i1+nsps8-1
if(i.lt.0 .or. i.gt.npts8-1) cycle
phi=phi + dphi
zsum=zsum + c0(i) * cmplx(cos(phi),-sin(phi))
enddo
sum=sum + real(zsum)**2 + aimag(zsum)**2
enddo
if(sum.gt.smax) then
idtpk=idt
smax=sum
endif
enddo
return
end subroutine peakdt9