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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+# AIFTRX -- Inverse discreet fourier transform (real transform, complex data
+# array in).  The input array A of length NPIX/2+1 contains the DC term and
+# the NPIX/2 (real,imag) pairs for each of the NPIX/2 harmonics of the real
+# transform.  Upon output array B contains the NPIX real data pixels from the
+# inverse transform.  The transform may be performed in place if desired.
+#
+# N.B.: The Fortran 77 standard guarantees that a complex datum is represented
+# as two reals, and that the first real in storage order is the real part of
+# the complex datum and the second real the imaginary part.  We have defined
+# B to be a type COMPLEX array in the calling program, but FFS expects a
+# REAL array containing (real,imag) pairs.  The Fortran standard appears to
+# guarantee that this will work.
+
+procedure aiftrx (a, b, npix)
+
+complex	a[ARB]			# transform, npix/2+1 elements
+real	b[ARB]			# output data array
+int	npix
+int	ier
+
+begin
+	# The following is a no-op if A and B are the same array.
+	call amovx (a, b, npix / 2 + 1)
+
+	# Compute the inverse real transform.
+	call ffs (b, npix, ier)
+	if (ier == 1)
+	    call fatal (1, "afftrx: npix not a power of 2")
+end