__P macro

>     I have been reading the OpenBSD source code and have been running
> across some structures||Macros i'm not understanding. Where would i
> look for more explanition about the  __P Macros.

  This is historical code...
  
  Old pre-ANSI compilers didn't support prototypes for functions.
  
  __P(X) was defined as emptiness on these platforms, therefore, function
prototypes always looked like 'int function()' .

  On ANSI compilers, __P(X) is defined as X, so function prototypes were
properly defined as 'int function(int a, double b)' .

  The __P macro was traditionnaly used to provide portability on both type
of compilers.

  Best regards,
  
          -Frank.