X-Git-Url: http://plrg.eecs.uci.edu/git/?p=folly.git;a=blobdiff_plain;f=folly%2FLikely.h;h=bdab72b817c2d621649c6bc28f27127aab6715be;hp=9a5aea99abd4ea6c69b25c9d086364527bc0e3db;hb=3579ddb46bf91312e7c1d24389ad60fd96fad776;hpb=dee8a5180aa542d98d1b71c74f83a006e4627952

diff --git a/folly/Likely.h b/folly/Likely.h
index 9a5aea99..bdab72b8 100644
--- a/folly/Likely.h
+++ b/folly/Likely.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 Facebook, Inc.
+ * Copyright 2012-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,19 +14,33 @@
  * limitations under the License.
  */
 
-/**
- * Compiler hints to indicate the fast path of an "if" branch: whether
- * the if condition is likely to be true or false.
- *
- * @author Tudor Bosman (tudorb@fb.com)
- */
-
 #pragma once
 
+#if __GNUC__
+#define FOLLY_DETAIL_BUILTIN_EXPECT(b, t) (__builtin_expect(b, t))
+#else
+#define FOLLY_DETAIL_BUILTIN_EXPECT(b, t) b
+#endif
+
+//  Likeliness annotations
+//
+//  Useful when the author has better knowledge than the compiler of whether
+//  the branch condition is overwhelmingly likely to take a specific value.
+//
+//  Useful when the author has better knowledge than the compiler of which code
+//  paths are designed as the fast path and which are designed as the slow path,
+//  and to force the compiler to optimize for the fast path, even when it is not
+//  overwhelmingly likely.
+
+#define FOLLY_LIKELY(x) FOLLY_DETAIL_BUILTIN_EXPECT((x), 1)
+#define FOLLY_UNLIKELY(x) FOLLY_DETAIL_BUILTIN_EXPECT((x), 0)
+
+//  Un-namespaced annotations
+
 #undef LIKELY
 #undef UNLIKELY
 
-#if defined(__GNUC__) && __GNUC__ >= 4
+#if defined(__GNUC__)
 #define LIKELY(x)   (__builtin_expect((x), 1))
 #define UNLIKELY(x) (__builtin_expect((x), 0))
 #else