Move some macros to a common header

1 files changed, 39 insertions, 0 deletions

diff --git a/common/opthelpers.h b/common/opthelpers.h
new file mode 100644
index 00000000..b496942c
--- /dev/null
+++ b/common/opthelpers.h
@@ -0,0 +1,39 @@
+#ifndef OPTHELPERS_H
+#define OPTHELPERS_H
+
+#ifdef __has_builtin
+#define HAS_BUILTIN __has_builtin
+#else
+#define HAS_BUILTIN(x) (0)
+#endif
+
+#ifdef __GNUC__
+/* LIKELY optimizes the case where the condition is true. The condition is not
+ * required to be true, but it can result in more optimal code for the true
+ * path at the expense of a less optimal false path.
+ */
+#define LIKELY(x) __builtin_expect(!!(x), !0)
+/* The opposite of LIKELY, optimizing the case where the condition is false. */
+#define UNLIKELY(x) __builtin_expect(!!(x), 0)
+/* Unlike LIKELY, ASSUME requires the condition to be true or else it invokes
+ * undefined behavior. It's essentially an assert without actually checking the
+ * condition at run-time, allowing for stronger optimizations than LIKELY.
+ */
+#if HAS_BUILTIN(__builtin_assume)
+#define ASSUME __builtin_assume
+#else
+#define ASSUME(x) do { if(!(x)) __builtin_unreachable(); } while(0)
+#endif
+
+#else /* __GNUC__ */
+
+#define LIKELY(x) (!!(x))
+#define UNLIKELY(x) (!!(x))
+#ifdef _MSC_VER
+#define ASSUME __assume
+#else
+#define ASSUME(x) ((void)0)
+#endif /* _MSC_VER */
+#endif /* __GNUC__ */
+
+#endif /* OPTHELPERS_H */