WSJT-X/lib/filbig.f90

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Fortran
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subroutine filbig(dd,npts,f0,newdat,c4a,n4,sq0)
! Filter and downsample the real data in array dd(npts), sampled at 12000 Hz.
! Output is complex, sampled at 1378.125 Hz.
use, intrinsic :: iso_c_binding
use FFTW3
parameter (NSZ=3413)
parameter (NFFT1=672000,NFFT2=77175)
parameter (NZ2=1000)
real*4 dd(npts) !Input data
real*4 rca(NFFT1)
complex ca(NFFT1/2+1) !FFT of input
complex c4a(NFFT2) !Output data
real*4 s(NZ2)
real*8 df
real halfpulse(8) !Impulse response of filter (one sided)
complex cfilt(NFFT2) !Filter (complex; imag = 0)
real rfilt(NFFT2) !Filter (real)
! integer*8 plan1,plan2,plan3
type(C_PTR) :: plan1,plan2,plan3 !Pointers to FFTW plans
logical first
! include 'fftw3.f90'
equivalence (rfilt,cfilt),(rca,ca)
data first/.true./
data halfpulse/114.97547150,36.57879257,-20.93789101, &
5.89886379,1.59355187,-2.49138308,0.60910773,-0.04248129/
common/refspec/dfref,ref(NSZ)
common/patience/npatience,nthreads
save first,plan1,plan2,plan3
if(npts.lt.0) go to 900 !Clean up at end of program
if(first) then
nflags=FFTW_ESTIMATE
if(npatience.eq.1) nflags=FFTW_ESTIMATE_PATIENT
if(npatience.eq.2) nflags=FFTW_MEASURE
if(npatience.eq.3) nflags=FFTW_PATIENT
if(npatience.eq.4) nflags=FFTW_EXHAUSTIVE
! Plan the FFTs just once
plan1=fftwf_plan_dft_r2c_1d(nfft1,rca,ca,nflags)
plan2=fftwf_plan_dft_1d(nfft2,c4a,c4a,-1,nflags)
plan3=fftwf_plan_dft_1d(nfft2,cfilt,cfilt,+1,nflags)
! Convert impulse response to filter function
do i=1,nfft2
cfilt(i)=0.
enddo
fac=0.00625/nfft1
cfilt(1)=fac*halfpulse(1)
do i=2,8
cfilt(i)=fac*halfpulse(i)
cfilt(nfft2+2-i)=fac*halfpulse(i)
enddo
call fftwf_execute_dft(plan3,cfilt,cfilt)
base=real(cfilt(nfft2/2+1))
do i=1,nfft2
rfilt(i)=real(cfilt(i))-base
enddo
df=12000.d0/nfft1
first=.false.
endif
! When new data comes along, we need to compute a new "big FFT"
! If we just have a new f0, continue with the existing data in ca.
if(newdat.ne.0) then
call timer('FFTbig ',0)
nz=min(npts,nfft1)
rca(1:nz)=dd(1:nz)
rca(nz+1:)=0.
call fftwf_execute_dft_r2c(plan1,rca,ca)
call timer('FFTbig ',1)
call timer('flatten ',0)
ib=0
do j=1,NSZ
ia=ib+1
ib=nint(j*dfref/df)
fac=sqrt(min(30.0,1.0/ref(j)))
ca(ia:ib)=fac*conjg(ca(ia:ib))
enddo
call timer('flatten ',1)
endif
! NB: f0 is the frequency at which we want our filter centered.
! i0 is the bin number in ca closest to f0.
call timer('loops ',0)
i0=nint(f0/df) + 1
nh=nfft2/2
do i=1,nh !Copy data into c4a and apply
j=i0+i-1 !the filter function
if(j.ge.1 .and. j.le.nfft1/2+1) then
c4a(i)=rfilt(i)*ca(j)
else
c4a(i)=0.
endif
enddo
do i=nh+1,nfft2
j=i0+i-1-nfft2
! if(j.lt.1) j=j+nfft1 !nfft1 was nfft2
if(j.ge.1) then
c4a(i)=rfilt(i)*ca(j)
else
c4a(i)=rfilt(i)*conjg(ca(2-j))
endif
enddo
nadd=nfft2/NZ2
i=0
do j=1,NZ2
s(j)=0.
do n=1,nadd
i=i+1
s(j)=s(j) + real(c4a(i))**2 + aimag(c4a(i))**2
enddo
enddo
call pctile(s,NZ2,30,sq0)
call timer('loops ',1)
! Do the short reverse transform, to go back to time domain.
call timer('FFTsmall',0)
call fftwf_execute_dft(plan2,c4a,c4a)
call timer('FFTsmall',1)
n4=min(npts/8,nfft2)
return
900 call fftwf_destroy_plan(plan1)
call fftwf_destroy_plan(plan2)
call fftwf_destroy_plan(plan3)
return
end subroutine filbig