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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+# AIFTRR -- Inverse fourier transform (real transform, real output arrays).
+# The inverse transform of the real arrays FR and FI of length NPIX/2+1 is
+# returned in the real array SR of length NPIX.  Since the real inverse
+# transform is being performed the array SI is ignored and may be omitted.
+# The transformation may be performed in place if desired.  NPIX must be a
+# power of 2.
+
+procedure aiftrr (fr, fi, sr, si, npix)
+
+real	fr[ARB], fi[ARB]	# real and imag parts of transform (input)
+real	sr[ARB], si[ARB]	# spatial data (output).  SI NOT USED.
+int	npix
+int	ier
+pointer	sp, work
+
+begin
+	call smark (sp)
+	call salloc (work, npix + 2, TY_REAL)
+
+	# Pack the real and imaginary parts into a complex array as required
+	# by FFS.
+	call apkxr (fr, fi, Memr[work], npix / 2 + 1)
+
+	# Compute the inverse transform.
+	call ffs (Memr[work], npix, ier)
+	if (ier == 1)
+	    call fatal (1, "aiftrr: npix not a power of 2")
+
+	# The work array now contains the real part of the transform; merely
+	# copy it to the output array.
+	call amovr (Memr[work], sr, npix)
+
+	call sfree (sp)
+end