Re Likely and Unlikely Macro

Hi In lxr, I saw the likely and unlikely macro defined as (compiler.h) # define likely(x) (__builtin_constant_p(x) ? !!(x) : __branch_check__(x, 1)) 116# endif 117# ifndef unlikely 118# define unlikely(x) (__builtin_constant_p(x) ? !!(x) : __branch_check__(x, 0)) 119# endif 120 ..... some other defines #else 146# define likely(x) __builtin_expect(!!(x), 1) 147# define unlikely(x) __builtin_expect(!!(x), 0) 148#endif I cannot understand the intention behind !!(x). Please can you let me know why !!(x) is required here. TIA -- ~/asd