X-Git-Url: http://git.ozlabs.org/?p=ccan;a=blobdiff_plain;f=ccan%2Filog%2Filog.h;h=32702b178567e503c11d606d655738fe9dbfc3aa;hp=9adbb8243f6c4f67da7ccefbc8fc7735f63cda7e;hb=1d14555d3a4501adae909884bcb8f8a0b142c89c;hpb=07dec048cb950abeb82c1447e523a2d22404b42a

diff --git a/ccan/ilog/ilog.h b/ccan/ilog/ilog.h
index 9adbb824..32702b17 100644
--- a/ccan/ilog/ilog.h
+++ b/ccan/ilog/ilog.h
@@ -120,7 +120,10 @@ int ilog64_nz(uint64_t _v) CONST_FUNCTION;
 #endif
 
 #ifdef builtin_ilog32_nz
-#define ilog32(_v) (builtin_ilog32_nz(_v)&-!!(_v))
+/* This used to be builtin_ilog32_nz(_v)&-!!(_v), which means it zeroes out
+ * the undefined builtin_ilog32_nz(0) return.  But clang UndefinedBehaviorSantizer
+ * complains, so do the branch: */
+#define ilog32(_v) ((_v) ? builtin_ilog32_nz(_v) : 0)
 #define ilog32_nz(_v) builtin_ilog32_nz(_v)
 #else
 #define ilog32_nz(_v) ilog32(_v)
@@ -128,7 +131,7 @@ int ilog64_nz(uint64_t _v) CONST_FUNCTION;
 #endif /* builtin_ilog32_nz */
 
 #ifdef builtin_ilog64_nz
-#define ilog64(_v) (builtin_ilog64_nz(_v)&-!!(_v))
+#define ilog32(_v) ((_v) ? builtin_ilog32_nz(_v) : 0)
 #define ilog64_nz(_v) builtin_ilog64_nz(_v)
 #else
 #define ilog64_nz(_v) ilog64(_v)