__has_attribute __has_builtin __has_extension __has_feature P99_ATLEAST P99_CONST_FUNCTION P99_DEPRECATED P99_EXPECT p99_extension P99_FIXED_REGISTER p99_has_attribute p99_has_builtin p99_has_extension p99_has_feature P99_IF_COMPILER p99_inline P99_LIKELY P99_MACRO_END P99_PARALLEL_PRAGMA P99_PURE_FUNCTION P99_SETJMP_INLINE P99_STRINGIFY P99_TENTATIVE_DEC P99_TENTATIVE_DEF P99_UNLIKELY P99_VECTOR P99_WARN_UNUSED_RESULT P99_WEAK static_inline

P99_UNLIKELY #define P99_UNLIKELY (   ... )    P99_EXPECT(!!(__VA_ARGS__), 0) Mark the conditional expression as being unlikely. This can be useful e.g to test returns of system functions. Many of these return 0 if everything goes well and something else otherwise. Use with care, as humans are particularly bad at branch prediction. If unsure, first test your conditional for some time to see that the case is really as unlikely as you think. See also P99_EXPECT P99_LIKELY Definition at line 994 of file p99_compiler.h.