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subroutine inter_wspr(id,ndir)
! Interleave (ndir=1) or de-interleave (ndir=-1) the array id.
integer*1 id(0:161),itmp(0:161)
integer j0(0:161)
logical first
data first/.true./
save
if(first) then
! Compute the interleave table using bit reversal.
k=-1
do i=0,255
n=0
ii=i
do j=0,7
n=n+n
if(iand(ii,1).ne.0) n=n+1
ii=ii/2
enddo
if(n.le.161) then
k=k+1
j0(k)=n
endif
enddo
first=.false.
endif
if(ndir.eq.1) then
do i=0,161
itmp(j0(i))=id(i)
enddo
else
do i=0,161
itmp(i)=id(j0(i))
enddo
endif
do i=0,161
id(i)=itmp(i)
enddo
return
end subroutine inter_wspr
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