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diff --git a/sys/imio/imsslv.x b/sys/imio/imsslv.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<imhdr.h>
+include	<imio.h>
+
+# IMSSLV -- Given two vectors (VS, VE) defining the starting and ending
+# physical coordinates of the two pixels defining an image section,
+# initialize the "loop index" vector V, and the "loop increment" vector,
+# VINC.  Compute NPIX, the number of pixels in a line segment.
+
+procedure imsslv (im, vs, ve, v, vinc, npix)
+
+pointer	im
+long	vs[IM_MAXDIM], ve[IM_MAXDIM]
+long	v[IM_MAXDIM], vinc[IM_MAXDIM], npix, step
+int	i
+
+begin
+	# Determine the direction in which each dimension is to be
+	# traversed.
+
+	do i = 1, IM_NPHYSDIM(im) {
+	    step = abs (IM_VSTEP(im,i))
+	    if (vs[i] <= ve[i])
+		vinc[i] = step
+	    else
+		vinc[i] = -step
+	}
+
+	# Initialize the extraction vector (passed to IMRDS? to read a
+	# contiguous array of pixels).  Compute the length of a line,
+	# allowing for decimation by the step size.
+
+	do i = 1, IM_NPHYSDIM(im)
+	    v[i] = vs[i]
+
+	if (vs[1] > ve[1])
+	    v[1] = ve[1]
+
+	npix = (ve[1] - vs[1]) / vinc[1] + 1
+end