common/opthelpers.h

   1 #ifndef OPTHELPERS_H
   2 #define OPTHELPERS_H
   3
   4 #ifdef __has_builtin
   5 #define HAS_BUILTIN __has_builtin
   6 #else
   7 #define HAS_BUILTIN(x) (0)
   8 #endif
   9
  10 #ifdef __GNUC__
  11 /* LIKELY optimizes the case where the condition is true. The condition is not
  12  * required to be true, but it can result in more optimal code for the true
  13  * path at the expense of a less optimal false path.
  14  */
  15 #define LIKELY(x) (__builtin_expect(!!(x), !false))
  16 /* The opposite of LIKELY, optimizing the case where the condition is false. */
  17 #define UNLIKELY(x) (__builtin_expect(!!(x), false))
  18 /* Unlike LIKELY, ASSUME requires the condition to be true or else it invokes
  19  * undefined behavior. It's essentially an assert without actually checking the
  20  * condition at run-time, allowing for stronger optimizations than LIKELY.
  21  */
  22 #if HAS_BUILTIN(__builtin_assume)
  23 #define ASSUME __builtin_assume
  24 #else
  25 #define ASSUME(x) do { if(!(x)) __builtin_unreachable(); } while(0)
  26 #endif
  27
  28 #else /* __GNUC__ */
  29
  30 #define LIKELY(x) (!!(x))
  31 #define UNLIKELY(x) (!!(x))
  32 #ifdef _MSC_VER
  33 #define ASSUME __assume
  34 #else
  35 #define ASSUME(x) ((void)0)
  36 #endif /* _MSC_VER */
  37 #endif /* __GNUC__ */
  38
  39 #endif /* OPTHELPERS_H */