Tell gcc about the value range.

* Otherwise, gcc assumes large numerical values of the time stamp
  components might lead to truncation of unitstr_.

src/stream_cdf_time.c

@@ -4,6 +4,7 @@
 
 #ifdef HAVE_LIBNETCDF
 
+#include <assert.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -88,8 +89,11 @@ cdfGetTimeUnits(taxis_t *taxis)
             timeunit = TUNIT_HOUR;
 
           char *unitstr_ = ptaxisAllocUnits(taxis, CDF_MAX_TIME_UNIT_STR);
-          snprintf(unitstr_, CDF_MAX_TIME_UNIT_STR, "%s since %d-%d-%d %02d:%02d:%02d", tunitNamePtr(timeunit), year, month, day,
-                   hour, minute, second);
+          assert(month >= 1 && month <= 12 && day > 0 && day <=31 &&
+                 hour >= 0 && hour <= 24 && minute >= 0 && minute < 60
+                 && second >= 0 && second <= 60);
+          snprintf(unitstr_, CDF_MAX_TIME_UNIT_STR, "%s since %d-%d-%d %02d:%02d:%02d", tunitNamePtr(timeunit), year, month&31, day&63,
+                   hour&63, minute&63, second&63);
           unitstr = unitstr_;
         }
     }