--- /dev/null
+/*
+ alloca -- (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.
+
+ It should work under any C implementation that uses an
+ actual procedure stack (as opposed to a linked list of
+ frames). 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.
+*/
+#ifndef lint
+static char SCCSid[] = "@(#)alloca.c 1.1"; /* for the "what" utility */
+#endif
+
+#ifdef emacs
+#include "config.h"
+#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 */
+
+#ifdef X3J11
+typedef void *pointer; /* generic pointer type */
+#else
+typedef char *pointer; /* generic pointer type */
+#endif
+
+#define NULL 0 /* null pointer constant */
+
+extern void Xfree();
+extern pointer Xalloc();
+
+/*
+ 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 = &dummy;
+
+ find_stack_direction (); /* recurse once */
+ }
+ else /* second entry */
+ if (&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;
+
+/*
+ alloca( size ) returns 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.
+*/
+
+static header *last_alloca_header = NULL; /* -> last alloca header */
+
+pointer
+alloca (size) /* returns pointer to storage */
+ unsigned size; /* # bytes to allocate */
+{
+ auto char probe; /* probes stack depth: */
+ register char *depth = &probe;
+
+#if STACK_DIRECTION == 0
+ if (STACK_DIR == 0) /* unknown growth direction */
+ find_stack_direction ();
+#endif
+
+ /* Reclaim garbage, defined as all alloca()ed 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;
+
+ Xfree ((pointer) 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 pointer new = Xalloc (sizeof (header) + size);
+ if (!new)
+ return NULL;
+ /* address of header */
+
+ ((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));
+ }
+}
+
projects / rdpsrv / blobdiff