WSJT-X/libm65/twkfreq.f

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subroutine twkfreq(c4aa,c4bb,n5,a)
complex c4aa(n5)
complex c4bb(n5)
real a(5)
complex w,wstep
data twopi/6.283185307/
C Apply AFC corrections to the c4aa and c4bb data
w=1.0
wstep=1.0
x0=0.5*(n5+1)
s=2.0/n5
do i=1,n5
x=s*(i-x0)
if(mod(i,1000).eq.1) then
p2=1.5*x*x - 0.5
! p3=2.5*(x**3) - 1.5*x
! p4=4.375*(x**4) - 3.75*(x**2) + 0.375
dphi=(a(1) + x*a(2) + p2*a(3)) * (twopi/1378.125)
wstep=cmplx(cos(dphi),sin(dphi))
endif
w=w*wstep
c4aa(i)=w*c4aa(i)
c4bb(i)=w*c4bb(i)
enddo
return
end