Make use of isnan optional since it's C99.

diff --git a/gpsbabel/grtcirc.c b/gpsbabel/grtcirc.c
index 752e3f229244eb0a875784444a8b03a919f50ea4..2bb40b0b2151ab42f33cf95fe6559a8d3cc6a815 100644 (file)
--- a/gpsbabel/grtcirc.c
+++ b/gpsbabel/grtcirc.c
@@ -68,7 +68,12 @@ double gcdist( double lat1, double lon1, double lat2, double lon2 ) {
 
   res = acos(res);
 
-  if ((isnan(res)) || (errno == EDOM)) { /* this should never happen: */
+  if (
+#if defined isnan
+         /* This is a C99-ism. */
+         (isnan(res)) || 
+#endif 
+         (errno == EDOM)) { /* this should never happen: */
     errno = 0;                           /* Math argument out of domain of function, */
     return 0;                            /* or value returned is not a number */
   }