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Aminet 24 (1998)(GTI - Schatztruhe)[!][Apr 1998].iso
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cxref_1_4a.lha
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alloca.c
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C/C++ Source or Header
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1997-11-20
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14KB
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496 lines
/* alloca.c -- allocate automatically reclaimed memory
(Mostly) portable public-domain implementation -- D A Gwyn
This implementation of the PWB library alloca function,
which is used to allocate space off the run-time stack so
that it is automatically reclaimed upon procedure exit,
was inspired by discussions with J. Q. Johnson of Cornell.
J.Otto Tennant <jot@cray.com> contributed the Cray support.
There are some preprocessor constants that can
be defined when compiling for your specific system, for
improved efficiency; however, the defaults should be okay.
The general concept of this implementation is to keep
track of all alloca-allocated blocks, and reclaim any
that are found to be deeper in the stack than the current
invocation. This heuristic does not reclaim storage as
soon as it becomes invalid, but it will do so eventually.
As a special case, alloca(0) reclaims storage without
allocating any. It is a good idea to use alloca(0) in
your main control loop, etc. to force garbage collection. */
#include <string.h>
#include <stdlib.h>
#ifdef emacs
#include "blockinput.h"
#endif
/* If compiling with GCC 2, this file's not needed. */
#if !defined (__GNUC__) || __GNUC__ < 2
/* If someone has defined alloca as a macro,
there must be some other way alloca is supposed to work. */
#ifndef alloca
#ifdef emacs
#ifdef static
/* actually, only want this if static is defined as ""
-- this is for usg, in which emacs must undefine static
in order to make unexec workable
*/
#ifndef STACK_DIRECTION
you
lose
-- must know STACK_DIRECTION at compile-time
#endif /* STACK_DIRECTION undefined */
#endif /* static */
#endif /* emacs */
/* If your stack is a linked list of frames, you have to
provide an "address metric" ADDRESS_FUNCTION macro. */
#if defined (CRAY) && defined (CRAY_STACKSEG_END)
long i00afunc ();
#define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
#else
#define ADDRESS_FUNCTION(arg) &(arg)
#endif
#if __STDC__
typedef void *pointer;
#else
typedef char *pointer;
#endif
#ifndef NULL
#define NULL 0
#endif
/* Different portions of Emacs need to call different versions of
malloc. The Emacs executable needs alloca to call xmalloc, because
ordinary malloc isn't protected from input signals. On the other
hand, the utilities in lib-src need alloca to call malloc; some of
them are very simple, and don't have an xmalloc routine.
Non-Emacs programs expect this to call use xmalloc.
Callers below should use malloc. */
/*#ifndef emacs*/
/*#define malloc xmalloc*/
/*#endif*/
/*extern pointer malloc ();*/
/* Define STACK_DIRECTION if you know the direction of stack
growth for your system; otherwise it will be automatically
deduced at run-time.
STACK_DIRECTION > 0 => grows toward higher addresses
STACK_DIRECTION < 0 => grows toward lower addresses
STACK_DIRECTION = 0 => direction of growth unknown */
#ifndef STACK_DIRECTION
#define STACK_DIRECTION 0 /* Direction unknown. */
#endif
#if STACK_DIRECTION != 0
#define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
#else /* STACK_DIRECTION == 0; need run-time code. */
static int stack_dir; /* 1 or -1 once known. */
#define STACK_DIR stack_dir
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. */
}
}
#endif /* STACK_DIRECTION == 0 */
/* An "alloca header" is used to:
(a) chain together all alloca'ed blocks;
(b) keep track of stack depth.
It is very important that sizeof(header) agree with malloc
alignment chunk size. The following default should work okay. */
#ifndef ALIGN_SIZE
#define ALIGN_SIZE sizeof(double)
#endif
typedef union hdr
{
char align[ALIGN_SIZE]; /* To force sizeof(header). */
struct
{
union hdr *next; /* For chaining headers. */
char *deep; /* For stack depth measure. */
} h;
} header;
static header *last_alloca_header = NULL; /* -> last alloca header. */
/* Return a pointer to at least SIZE bytes of storage,
which will be automatically reclaimed upon exit from
the procedure that called alloca. Originally, this space
was supposed to be taken from the current stack frame of the
caller, but that method cannot be made to work for some
implementations of C, for example under Gould's UTX/32. */
pointer
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. */
#ifdef emacs
BLOCK_INPUT;
#endif
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 ((pointer) hp); /* Collect garbage. */
hp = np; /* -> next header. */
}
else
break; /* Rest are not deeper. */
last_alloca_header = hp; /* -> last valid storage. */
#ifdef emacs
UNBLOCK_INPUT;
#endif
}
if (size == 0)
return NULL; /* No allocation required. */
/* Allocate combined header + user data storage. */
{
register pointer new = malloc (sizeof (header) + size);
/* Address of header. */
if (new == 0)
abort();
((header *) new)->h.next = last_alloca_header;
((header *) new)->h.deep = depth;
last_alloca_header = (header *) new;
/* User storage begins just after header. */
return (pointer) ((char *) new + sizeof (header));
}
}
#if defined (CRAY) && defined (CRAY_STACKSEG_END)
#ifdef DEBUG_I00AFUNC
#include <stdio.h>
#endif
#ifndef CRAY_STACK
#define CRAY_STACK
#ifndef CRAY2
/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
struct stack_control_header
{
long shgrow:32; /* Number of times stack has grown. */
long shaseg:32; /* Size of increments to stack. */
long shhwm:32; /* High water mark of stack. */
long shsize:32; /* Current size of stack (all segments). */
};
/* The stack segment linkage control information occurs at
the high-address end of a stack segment. (The stack
grows from low addresses to high addresses.) The initial
part of the stack segment linkage control information is
0200 (octal) words. This provides for register storage
for the routine which overflows the stack. */
struct stack_segment_linkage
{
long ss[0200]; /* 0200 overflow words. */
long sssize:32; /* Number of words in this segment. */
long ssbase:32; /* Offset to stack base. */
long:32;
long sspseg:32; /* Offset to linkage control of previous
segment of stack. */
long:32;
long sstcpt:32; /* Pointer to task common address block. */
long sscsnm; /* Private control structure number for
microtasking. */
long ssusr1; /* Reserved for user. */
long ssusr2; /* Reserved for user. */
long sstpid; /* Process ID for pid based multi-tasking. */
long ssgvup; /* Pointer to multitasking thread giveup. */
long sscray[7]; /* Reserved for Cray Research. */
long ssa0;
long ssa1;
long ssa2;
long ssa3;
long ssa4;
long ssa5;
long ssa6;
long ssa7;
long sss0;
long sss1;
long sss2;
long sss3;
long sss4;
long sss5;
long sss6;
long sss7;
};
#else /* CRAY2 */
/* The following structure defines the vector of words
returned by the STKSTAT library routine. */
struct stk_stat
{
long now; /* Current total stack size. */
long maxc; /* Amount of cont