static void find_stack_direction()
{
static char *addr = NULL; /* Address of first `dummy', once known. */
auto char dummy; /* To get stack address. */
if (addr == NULL) { /* Initial entry. */
addr = ADDRESS_FUNCTION(dummy);
find_stack_direction(); /* Recurse once. */
} else {
/* Second entry. */
if (ADDRESS_FUNCTION(dummy) > addr)
stack_dir = 1; /* Stack grew upward. */
else
stack_dir = -1; /* Stack grew downward. */
}
}
static void
find_stack_direction (/* void */)
{
static char *addr = NULL; /* address of first
`dummy', once known */
auto char dummy; /* to get stack address */
if (addr == NULL)
{ /* initial entry */
addr = ADDRESS_FUNCTION(dummy);
find_stack_direction (); /* recurse once */
}
else /* second entry */
if (ADDRESS_FUNCTION(dummy) > addr)
stack_dir = 1; /* stack grew upward */
else
stack_dir = -1; /* stack grew downward */
}
static void
find_stack_direction (char **ptr)
{
auto char dummy; /* To get stack address. */
if (*ptr == NULL)
{ /* Initial entry. */
*ptr = ADDRESS_FUNCTION (dummy);
find_stack_direction (ptr); /* Recurse once. */
}
else
{
/* Second entry. */
if (ADDRESS_FUNCTION (dummy) > *ptr)
stack_dir = 1; /* Stack grew upward. */
else
stack_dir = -1; /* Stack grew downward. */
}
}
void *
alloca (unsigned size)
{
auto char probe; /* Probes stack depth: */
register char *depth = ADDRESS_FUNCTION (probe);
#if STACK_DIRECTION == 0
if (STACK_DIR == 0) /* Unknown growth direction. */
find_stack_direction ();
#endif
/* Reclaim garbage, defined as all alloca'd storage that
was allocated from deeper in the stack than currently. */
{
register header *hp; /* Traverses linked list. */
for (hp = last_alloca_header; hp != NULL;)
if ((STACK_DIR > 0 && hp->h.deep > depth)
|| (STACK_DIR < 0 && hp->h.deep < depth))
{
register header *np = hp->h.next;
free ((void *) hp); /* Collect garbage. */
hp = np; /* -> next header. */
}
else
break; /* Rest are not deeper. */
last_alloca_header = hp; /* -> last valid storage. */
}
if (size == 0)
return NULL; /* No allocation required. */
/* Allocate combined header + user data storage. */
{
register void * newptr = malloc (sizeof (header) + size);
/* Address of header. */
((header *) newptr)->h.next = last_alloca_header;
((header *) newptr)->h.deep = depth;
last_alloca_header = (header *) newptr;
/* User storage begins just after header. */
return (void *) ((char *) newptr + sizeof (header));
}
}