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! Calculation of centered differences.
! $Header$
if ( eh_mask(i,j,k,l) .ge. 0 ) then
if ( ( .not. btest(eh_mask(i,j,k,l),0) ) .and. &
( .not. btest(eh_mask(i,j,k,l),1) ) ) then
dfx(i,j,k,l) = idx * ( f(i+1,j,k,l) - f(i-1,j,k,l) )
else if ( btest(eh_mask(i,j,k,l),0) ) then
dfx(i,j,k,l) = idx * ( -three * f(i,j,k,l) + &
four * f(i+1,j,k,l) - f(i+2,j,k,l) )
else
dfx(i,j,k,l) = idx * ( three * f(i,j,k,l) - &
four * f(i-1,j,k,l) + f(i-2,j,k,l) )
end if
if ( ( .not. btest(eh_mask(i,j,k,l),2) ) .and. &
( .not. btest(eh_mask(i,j,k,l),3) ) ) then
dfy(i,j,k,l) = idy * ( f(i,j+1,k,l) - f(i,j-1,k,l) )
else if ( btest(eh_mask(i,j,k,l),2) ) then
dfy(i,j,k,l) = idy * ( -three * f(i,j,k,l) + &
four * f(i,j+1,k,l) - f(i,j+2,k,l) )
else
dfy(i,j,k,l) = idy * ( three * f(i,j,k,l) - &
four * f(i,j-1,k,l) + f(i,j-2,k,l) )
end if
if ( ( .not. btest(eh_mask(i,j,k,l),4) ) .and. &
( .not. btest(eh_mask(i,j,k,l),5) ) ) then
dfz(i,j,k,l) = idz * ( f(i,j,k+1,l) - f(i,j,k-1,l) )
else if ( btest(eh_mask(i,j,k,l),4) ) then
dfz(i,j,k,l) = idz * ( -three * f(i,j,k,l) + &
four * f(i,j,k+1,l) - f(i,j,k+2,l) )
else
dfz(i,j,k,l) = idz * ( three * f(i,j,k,l) - &
four * f(i,j,k-1,l) + f(i,j,k-2,l) )
end if
else
dfx(i,j,k,l) = zero
dfy(i,j,k,l) = zero
dfz(i,j,k,l) = zero
end if
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