util: New function raw_ctz().

This will acquire a user in an upcoming commit.

Signed-off-by: Ben Pfaff <blp@nicira.com>

1 files changed, 24 insertions, 1 deletions

diff --git a/lib/util.h b/lib/util.h
index a8d86657..a1f4bd74 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -242,9 +242,32 @@ char *xreadlink(const char *filename);
 char *follow_symlinks(const char *filename);
 
 void ignore(bool x OVS_UNUSED);
+
+/* Returns the number of trailing 0-bits in 'n'.  Undefined if 'n' == 0.
+ *
+ * This compiles to a single machine instruction ("bsf") with GCC on x86. */
+#if !defined(UINT_MAX) || !defined(UINT32_MAX)
+#error "Someone screwed up the #includes."
+#elif __GNUC__ >= 4 && UINT_MAX == UINT32_MAX
+static inline int
+raw_ctz(uint32_t n)
+{
+    return __builtin_ctz(n);
+}
+#else
+/* Defined in util.c. */
+int raw_ctz(uint32_t n);
+#endif
+
+/* Returns the number of trailing 0-bits in 'n', or 32 if 'n' is 0. */
+static inline int
+ctz(uint32_t n)
+{
+    return n ? raw_ctz(n) : 32;
+}
+
 int log_2_floor(uint32_t);
 int log_2_ceil(uint32_t);
-int ctz(uint32_t);
 int popcount(uint32_t);
 
 bool is_all_zeros(const uint8_t *, size_t);