--- MITgcm/pkg/cal/cal_convdate.F	2001/05/14 22:07:26	1.1
+++ MITgcm/pkg/cal/cal_convdate.F	2003/10/02 18:30:07	1.3.2.1
@@ -1,6 +1,6 @@
-C $Header: /home/ubuntu/mnt/e9_copy/MITgcm/pkg/cal/cal_convdate.F,v 1.1 2001/05/14 22:07:26 heimbach Exp $
+C $Header: /home/ubuntu/mnt/e9_copy/MITgcm/pkg/cal/cal_convdate.F,v 1.3.2.1 2003/10/02 18:30:07 adcroft Exp $
 
-#include "CAL_CPPOPTIONS.h"
+#include "CAL_OPTIONS.h"
 
       subroutine cal_ConvDate(
      I                         date,
@@ -27,6 +27,9 @@
 c              - Introduced new routine and function names, cal_<NAME>,
 c                for verion 0.1.3.
 c
+c              21-Sep-2003: fixed check_sign logic to work with
+c              negative intervals (menemenlis@jpl.nasa.gov)
+c
 c     ==================================================================
 c     SUBROUTINE cal_ConvDate
 c     ==================================================================
@@ -53,9 +56,8 @@
       integer fac
       integer date_1
       integer date_2
-      integer check_sign_1
-      integer check_sign_2
       integer ierr
+      integer check_sign
 
 c     == end of interface ==
 
@@ -63,10 +65,12 @@
 
 c     Check the sign of the date.
 
-      check_sign_1 = sign(1,date(1))
-      check_sign_2 = sign(1,date(2))
+      check_sign = 1
+      if ( ( (date(1).lt.0) .and. date(2).gt.0 ) .or.
+     &     ( (date(1).gt.0) .and. date(2).lt.0 ) )
+     &     check_sign = -1
 
-      if ( check_sign_1*check_sign_2 .ge. 0 ) then
+      if ( check_sign .ge. 0 ) then
         if (date(1) .eq. 0) then
           date_1 = date(1)
           if (date(2) .lt. 0) then