src/include/stdarg.h

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/* The <stdarg.h> header is ANSI's way to handle variable numbers of params.
 * Some programming languages require a function that is declared with n
 * parameters to be called with n parameters.  C does not.  A function may
 * called with more parameters than it is declared with.  The well-known
 * printf function, for example, may have arbitrarily many parameters.
 * The question arises how one can access all the parameters in a portable
 * way.  The C standard defines three macros that programs can use to
 * advance through the parameter list.  The definition of these macros for
 * MINIX are given in this file.  The three macros are:
 *
 *      va_start(ap, parmN)     prepare to access parameters
 *      va_arg(ap, type)        get next parameter value and type
 *      va_end(ap)              access is finished
 *
 * Ken Thompson's famous line from V6 UNIX is equally applicable to this file:
 *
 *      "You are not expected to understand this"
 *
 */

#ifndef _STDARG_H
#define _STDARG_H

#ifdef __GNUC__
/* The GNU C-compiler uses its own, but similar varargs mechanism. */

typedef char *va_list;

/* Amount of space required in an argument list for an arg of type TYPE.
 * TYPE may alternatively be an expression whose type is used.
 */

#define __va_rounded_size(TYPE)  \
  (((sizeof (TYPE) + sizeof (int) - 1) / sizeof (int)) * sizeof (int))

#if __GNUC__ < 2

#ifndef __sparc__
#define va_start(AP, LASTARG)                                           \
 (AP = ((char *) &(LASTARG) + __va_rounded_size (LASTARG)))
#else
#define va_start(AP, LASTARG)                                           \
 (__builtin_saveregs (),                                                \
  AP = ((char *) &(LASTARG) + __va_rounded_size (LASTARG)))
#endif

void va_end (va_list);          /* Defined in gnulib */
#define va_end(AP)

#define va_arg(AP, TYPE)                                                \
 (AP += __va_rounded_size (TYPE),                                       \
  *((TYPE *) (AP - __va_rounded_size (TYPE))))

#else   /* __GNUC__ >= 2 */

#ifndef __sparc__
#define va_start(AP, LASTARG)                                           \
 (AP = ((char *) __builtin_next_arg ()))
#else
#define va_start(AP, LASTARG)                                   \
  (__builtin_saveregs (), AP = ((char *) __builtin_next_arg ()))
#endif

void va_end (va_list);          /* Defined in libgcc.a */
#define va_end(AP)

#define va_arg(AP, TYPE)                                                \
 (AP = ((char *) (AP)) += __va_rounded_size (TYPE),                     \
  *((TYPE *) ((char *) (AP) - __va_rounded_size (TYPE))))

#endif  /* __GNUC__ >= 2 */

#else   /* not __GNUC__ */

typedef char *va_list;

#define __vasz(x)               ((sizeof(x)+sizeof(int)-1) & ~(sizeof(int) -1))

#define va_start(ap, parmN)     ((ap) = (va_list)&parmN + __vasz(parmN))
#define va_arg(ap, type)      \
  (*((type *)((va_list)((ap) = (void *)((va_list)(ap) + __vasz(type))) \
                                                    - __vasz(type))))
#define va_copy(ap2, ap) (ap2) = (ap)
#define va_end(ap)

#endif /* __GNUC__ */

#endif /* _STDARG_H */

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