/*
- * Copyright 2012 Facebook, Inc.
+ * Copyright 2011-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.
* 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
-#ifndef FOLLY_BASE_LIKELY_H_
-#define FOLLY_BASE_LIKELY_H_
+// 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
#define LIKELY(x) (x)
#define UNLIKELY(x) (x)
#endif
-
-#endif /* FOLLY_BASE_LIKELY_H_ */
-