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diff --git a/sys/vops/ak/ahgmi.x b/sys/vops/ak/ahgmi.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<mach.h>
+
+# AHGM -- Accumulate the histogram of the input vector.  The output vector
+# HGM (the histogram) should be cleared prior to the first call.
+
+procedure ahgmi (data, npix, hgm, nbins, z1, z2)
+
+int 	data[ARB]		# data vector
+int	npix			# number of pixels
+int	hgm[ARB]		# output histogram
+int	nbins			# number of bins in histogram
+int	z1, z2			# greyscale values of first and last bins
+
+int	z
+real	dz
+int	bin, i
+
+begin
+	dz = real (nbins - 1) / real (z2 - z1)
+	if (abs (dz - 1.0) < (EPSILONR * 2.0)) {
+	    do i = 1, npix {
+		z = data[i]
+		if (z >= z1 && z <= z2) {
+		    bin = int (z - z1) + 1
+		    hgm[bin] = hgm[bin] + 1
+		}
+	    }
+	} else {
+	    do i = 1, npix {
+		z = data[i]
+		if (z >= z1 && z <= z2) {
+		    bin = int ((z - z1) * dz) + 1
+		    hgm[bin] = hgm[bin] + 1
+		}
+	    }
+	}
+end