handy.h: Avoid compiler warnings for withinCOUNT()

If a parameter to this function is unsigned, gcc, at least, generates a
comparison-always-true warning for the asserts on the parameters.
Silence these by casting to an NV.  Any extra machine instructions will
be gone from non-DEBUGGING builds.  The value in an NV won't necessarily
be exact, but all the assertions care about is the sign, which is
guaranteed by C11 standard 6.3.1.4 item 2.

This technique was the idea of Tomasz Konojacki.

diff --git a/handy.h b/handy.h
index e584efd..26547fb 100644 (file)
--- a/handy.h
+++ b/handy.h
@@ -1319,9 +1319,12 @@ or casts
 
 /* Returns true if l <= c <= (l + n), where 'l' and 'n' are non-negative
  * Written this way so that after optimization, only one conditional test is
- * needed. */
-#define withinCOUNT(c, l, n) (__ASSERT_((l) >= 0) __ASSERT_((n) >= (0))        \
-   (((WIDEST_UTYPE) (((c) | 0) - ((l) | 0))) <= (((WIDEST_UTYPE) ((n) | 0)))))
+ * needed.  (The NV casts stop any warnings about comparison always being true
+ * if called with an unsigned.  The cast preserves the sign, which is all we
+ * care about.) */
+#define withinCOUNT(c, l, n) (__ASSERT_((NV) (l) >= 0)                         \
+                              __ASSERT_((NV) (n) >= 0)                         \
+   (((WIDEST_UTYPE) (((c)) - ((l) | 0))) <= (((WIDEST_UTYPE) ((n) | 0)))))
 
 /* Returns true if c is in the range l..u, where 'l' is non-negative
  * Written this way so that after optimization, only one conditional test is