netdissect.h: Update ND_TTEST2 to fix issue 443

Add IS_NOT_NEGATIVE macro.
Avoid these warnings:
- comparison of unsigned expression >= 0 is always true [-Wtype-limits],
- comparison is always true due to limited range of data type [-Wtype-limits].

diff --git a/netdissect.h b/netdissect.h
index c377b62208048354088e38067c5893d49d1e59bb..9e369a994381fb332930eb9246d6b67139da4688 100644 (file)
--- a/netdissect.h
+++ b/netdissect.h
@@ -270,8 +270,11 @@ struct netdissect_options {
  *
  *     http://www.kb.cert.org/vuls/id/162289
  */
+
+#define IS_NOT_NEGATIVE(x) (((x) > 0) || ((x) == 0))
+
 #define ND_TTEST2(var, l) \
-  ((l) >= 0 && \
+  (IS_NOT_NEGATIVE(l) && \
        ((uintptr_t)ndo->ndo_snapend - (l) <= (uintptr_t)ndo->ndo_snapend && \
          (uintptr_t)&(var) <= (uintptr_t)ndo->ndo_snapend - (l)))