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diff --git a/src/slalib/drange.f b/src/slalib/drange.f
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+      DOUBLE PRECISION FUNCTION sla_DRANGE (ANGLE)
+*+
+*     - - - - - - -
+*      D R A N G E
+*     - - - - - - -
+*
+*  Normalize angle into range +/- pi  (double precision)
+*
+*  Given:
+*     ANGLE     dp      the angle in radians
+*
+*  The result (double precision) is ANGLE expressed in the range +/- pi.
+*
+*  P.T.Wallace   Starlink   23 November 1995
+*
+*  Copyright (C) 1995 Rutherford Appleton Laboratory
+*-
+
+      IMPLICIT NONE
+
+      DOUBLE PRECISION ANGLE
+
+      DOUBLE PRECISION DPI,D2PI
+      PARAMETER (DPI=3.141592653589793238462643D0)
+      PARAMETER (D2PI=6.283185307179586476925287D0)
+
+
+      sla_DRANGE=MOD(ANGLE,D2PI)
+      IF (ABS(sla_DRANGE).GE.DPI)
+     :          sla_DRANGE=sla_DRANGE-SIGN(D2PI,ANGLE)
+
+      END