include/stdarg.h

   1 /* The <stdarg.h> header is ANSI's way to handle variable numbers of params.
   2  * Some programming languages require a function that is declared with n
   3  * parameters to be called with n parameters.  C does not.  A function may
   4  * called with more parameters than it is declared with.  The well-known
   5  * printf function, for example, may have arbitrarily many parameters.
   6  * The question arises how one can access all the parameters in a portable
   7  * way.  The C standard defines three macros that programs can use to
   8  * advance through the parameter list.  The definition of these macros for
   9  * MINIX are given in this file.  The three macros are:
  10  *
  11  *      va_start(ap, parmN)     prepare to access parameters
  12  *      va_arg(ap, type)        get next parameter value and type
  13  *      va_end(ap)              access is finished
  14  *
  15  * Ken Thompson's famous line from V6 UNIX is equally applicable to this file:
  16  *
  17  *      "You are not expected to understand this"
  18  *
  19  */
  20
  21 #ifndef _STDARG_H
  22 #define _STDARG_H
  23
  24 #ifdef __GNUC__
  25 /* The GNU C-compiler uses its own, but similar varargs mechanism. */
  26
  27 typedef char *va_list;
  28
  29 /* Amount of space required in an argument list for an arg of type TYPE.
  30  * TYPE may alternatively be an expression whose type is used.
  31  */
  32
  33 #define __va_rounded_size(TYPE)  \
  34   (((sizeof (TYPE) + sizeof (int) - 1) / sizeof (int)) * sizeof (int))
  35
  36 #if __GNUC__ < 2
  37
  38 #ifndef __sparc__
  39 #define va_start(AP, LASTARG)                                           \
  40  (AP = ((char *) &(LASTARG) + __va_rounded_size (LASTARG)))
  41 #else
  42 #define va_start(AP, LASTARG)                                           \
  43  (__builtin_saveregs (),                                                \
  44   AP = ((char *) &(LASTARG) + __va_rounded_size (LASTARG)))
  45 #endif
  46
  47 void va_end (va_list);          /* Defined in gnulib */
  48 #define va_end(AP)
  49
  50 #define va_arg(AP, TYPE)                                                \
  51  (AP += __va_rounded_size (TYPE),                                       \
  52   *((TYPE *) (AP - __va_rounded_size (TYPE))))
  53
  54 #else   /* __GNUC__ >= 2 */
  55
  56 #define va_start(ap, last) __builtin_va_start((ap), (last))
  57 #define va_arg(ap, type) __builtin_va_arg((ap), type)
  58 #define va_end(ap) __builtin_va_end(ap)
  59 #define va_copy(dest, src) __builtin_va_copy((dest), (src))
  60
  61 #endif  /* __GNUC__ >= 2 */
  62
  63 #else   /* not __GNUC__ */
  64
  65 typedef char *va_list;
  66
  67 #define __vasz(x)               ((sizeof(x)+sizeof(int)-1) & ~(sizeof(int) -1))
  68
  69 #define va_start(ap, parmN)     ((ap) = (va_list)&parmN + __vasz(parmN))
  70 #define va_arg(ap, type)      \
  71   (*((type *)((va_list)((ap) = (void *)((va_list)(ap) + __vasz(type))) \
  72                                                     - __vasz(type))))
  73 #define va_copy(ap2, ap) (ap2) = (ap)
  74 #define va_end(ap)
  75
  76 #endif /* __GNUC__ */
  77
  78 #endif /* _STDARG_H */