20010102-1.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

/* This testcase derives from gnu obstack.c/obstack.h and failed with
   -O3 -funroll-all-loops, or -O1 -frename-registers -funroll-loops on
   sparc-sun-solaris2.7.

   Copyright (C) 2001  Free Software Foundation.  */

# define PTR_INT_TYPE __PTRDIFF_TYPE__

struct _obstack_chunk
{
  char  *limit;
  struct _obstack_chunk *prev;
  char	contents[4];
};

struct obstack
{
  long	chunk_size;
  struct _obstack_chunk *chunk;
  char	*object_base;
  char	*next_free;
  char	*chunk_limit;
  PTR_INT_TYPE temp;
  int   alignment_mask;
  struct _obstack_chunk *(*chunkfun) (void *, long);
  void (*freefun) (void *, struct _obstack_chunk *);
  void *extra_arg;
  unsigned use_extra_arg:1;
  unsigned maybe_empty_object:1;
  unsigned alloc_failed:1;
};

extern void _obstack_newchunk (struct obstack *, int);

struct fooalign {char x; double d;};
#define DEFAULT_ALIGNMENT  \
  ((PTR_INT_TYPE) ((char *) &((struct fooalign *) 0)->d - (char *) 0))
union fooround {long x; double d;};
#define DEFAULT_ROUNDING (sizeof (union fooround))

#ifndef COPYING_UNIT
#define COPYING_UNIT int
#endif

#define CALL_CHUNKFUN(h, size) \
  (((h) -> use_extra_arg) \
   ? (*(h)->chunkfun) ((h)->extra_arg, (size)) \
   : (*(struct _obstack_chunk *(*) (long)) (h)->chunkfun) ((size)))

#define CALL_FREEFUN(h, old_chunk) \
  do { \
    if ((h) -> use_extra_arg) \
      (*(h)->freefun) ((h)->extra_arg, (old_chunk)); \
    else \
      (*(void (*) (void *)) (h)->freefun) ((old_chunk)); \
  } while (0)

void
_obstack_newchunk (h, length)
     struct obstack *h;
     int length;
{
  register struct _obstack_chunk *old_chunk = h->chunk;
  register struct _obstack_chunk *new_chunk;
  register long	new_size;
  register long obj_size = h->next_free - h->object_base;
  register long i;
  long already;

  new_size = (obj_size + length) + (obj_size >> 3) + 100;
  if (new_size < h->chunk_size)
    new_size = h->chunk_size;

  new_chunk = CALL_CHUNKFUN (h, new_size);
  h->chunk = new_chunk;
  new_chunk->prev = old_chunk;
  new_chunk->limit = h->chunk_limit = (char *) new_chunk + new_size;

  if (h->alignment_mask + 1 >= DEFAULT_ALIGNMENT)
    {
      for (i = obj_size / sizeof (COPYING_UNIT) - 1;
	   i >= 0; i--)
	((COPYING_UNIT *)new_chunk->contents)[i]
	  = ((COPYING_UNIT *)h->object_base)[i];
      already = obj_size / sizeof (COPYING_UNIT) * sizeof (COPYING_UNIT);
    }
  else
    already = 0;
  for (i = already; i < obj_size; i++)
    new_chunk->contents[i] = h->object_base[i];

  if (h->object_base == old_chunk->contents && ! h->maybe_empty_object)
    {
      new_chunk->prev = old_chunk->prev;
      CALL_FREEFUN (h, old_chunk);
    }

  h->object_base = new_chunk->contents;
  h->next_free = h->object_base + obj_size;
  h->maybe_empty_object = 0;
}