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diff --git a/sys/vops/lz/alogd.x b/sys/vops/lz/alogd.x
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+++ b/sys/vops/lz/alogd.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+# ALOG -- Compute the logarithm to the base 10 of a vector (generic).  If the
+# logarithm is undefined (x <= 0) a user supplied function is called to get
+# the function value.
+
+procedure alogd (a, b, npix, errfcn)
+
+double	a[ARB], b[ARB]
+int	npix, i
+extern	errfcn()
+double	errfcn()
+errchk	errfcn
+
+begin
+	do i = 1, npix {
+		if (a[i] <= 0.0D0)
+		    b[i] = errfcn (a[i])
+		else {
+		    # Note Fortran standard forbids log10(cplx).
+			b[i] = log10 (a[i])
+		}
+	}
+end