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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
include <mach.h>
# ALUI -- Vector lookup and interpolate (linear). B[i] = A(X[i]).
# No bounds checking is performed, but the case A(X[i])=NPIX (no fractional
# part) is recognized and will not cause a reference off the right end of the
# array. This is done in a way which will also cause execution to be faster
# when the sample points are integral, i.e., fall exactly on data points in
# the input array.
procedure aluir (a, b, x, npix)
real a[ARB], b[ARB]
real x[ARB], fraction, tol
int npix, i, left_pixel
begin
tol = EPSILONR * 5.0
do i = 1, npix {
left_pixel = int (x[i])
fraction = x[i] - real(left_pixel)
if (fraction < tol)
b[i] = a[left_pixel]
else
b[i] = a[left_pixel] * (1.0 - fraction) +
a[left_pixel+1] * fraction
}
end
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