WSJT-X/libm65/filbig.f90

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3.8 KiB
Fortran
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subroutine filbig(dd,nmax,f0,newdat,nfsample,xpol,c4a,c4b,n4)
! Filter and downsample complex data stored in array dd(4,nmax).
! Output is downsampled from 96000 Hz to 1375.125 Hz.
parameter (MAXFFT1=5376000,MAXFFT2=77175)
real*4 dd(4,nmax) !Input data
complex ca(MAXFFT1),cb(MAXFFT1) !FFTs of input
complex c4a(MAXFFT2),c4b(MAXFFT2) !Output data
real*8 df
real halfpulse(8) !Impulse response of filter (one sided)
complex cfilt(MAXFFT2) !Filter (complex; imag = 0)
real rfilt(MAXFFT2) !Filter (real)
integer*8 plan1,plan2,plan3,plan4,plan5
logical first,xpol
include 'fftw3.f'
common/cacb/ca,cb
equivalence (rfilt,cfilt)
data first/.true./,npatience/1/
data halfpulse/114.97547150,36.57879257,-20.93789101, &
5.89886379,1.59355187,-2.49138308,0.60910773,-0.04248129/
save
if(nmax.lt.0) go to 900
nfft1=MAXFFT1
nfft2=MAXFFT2
if(nfsample.eq.95238) then
nfft1=5120000
nfft2=74088
endif
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
call timer('FFTplans ',0)
call sfftw_plan_dft_1d(plan1,nfft1,ca,ca,FFTW_BACKWARD,nflags)
call sfftw_plan_dft_1d(plan2,nfft1,cb,cb,FFTW_BACKWARD,nflags)
call sfftw_plan_dft_1d(plan3,nfft2,c4a,c4a,FFTW_FORWARD,nflags)
call sfftw_plan_dft_1d(plan4,nfft2,c4b,c4b,FFTW_FORWARD,nflags)
call sfftw_plan_dft_1d(plan5,nfft2,cfilt,cfilt,FFTW_BACKWARD,nflags)
call timer('FFTplans ',1)
! 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 timer('FFTfilt ',0)
call sfftw_execute(plan5)
call timer('FFTfilt ',1)
base=cfilt(nfft2/2+1)
do i=1,nfft2
rfilt(i)=real(cfilt(i))-base
enddo
df=96000.d0/nfft1
if(nfsample.eq.95238) df=95238.1d0/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 ca and cb.
if(newdat.ne.0) then
nz=min(nmax,nfft1)
do i=1,nz
ca(i)=cmplx(dd(1,i),dd(2,i))
if(xpol) cb(i)=cmplx(dd(3,i),dd(4,i))
enddo
if(nmax.lt.nfft1) then
do i=nmax+1,nfft1
ca(i)=0.
if(xpol) cb(i)=0.
enddo
endif
call timer('FFTbig ',0)
call sfftw_execute(plan1)
if(xpol) call sfftw_execute(plan2)
call timer('FFTbig ',1)
newdat=0
endif
! NB: f0 is the frequency at which we want our filter centered.
! i0 is the bin number in ca and cb closest to f0.
i0=nint(f0/df) + 1
nh=nfft2/2
do i=1,nh !Copy data into c4a and c4b,
j=i0+i-1 !and apply the filter function
if(j.ge.1 .and. j.le.nfft1) then
c4a(i)=rfilt(i)*ca(j)
if(xpol) c4b(i)=rfilt(i)*cb(j)
else
c4a(i)=0.
if(xpol) c4b(i)=0.
endif
enddo
do i=nh+1,nfft2
j=i0+i-1-nfft2
if(j.lt.1) j=j+nfft1 !nfft1 was nfft2
c4a(i)=rfilt(i)*ca(j)
if(xpol) c4b(i)=rfilt(i)*cb(j)
enddo
! Do the short reverse transform, to go back to time domain.
call timer('FFTsmall',0)
call sfftw_execute(plan3)
if(xpol) call sfftw_execute(plan4)
call timer('FFTsmall',1)
n4=min(nmax/64,nfft2)
go to 999
900 call sfftw_destroy_plan(plan1)
call sfftw_destroy_plan(plan2)
call sfftw_destroy_plan(plan3)
call sfftw_destroy_plan(plan4)
call sfftw_destroy_plan(plan5)
999 return
end subroutine filbig