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Diffstat (limited to 'missing/alloca.c')
| -rw-r--r-- | missing/alloca.c | 189 |
1 files changed, 0 insertions, 189 deletions
diff --git a/missing/alloca.c b/missing/alloca.c deleted file mode 100644 index 6879618c8a..0000000000 --- a/missing/alloca.c +++ /dev/null @@ -1,189 +0,0 @@ -/* alloca -- (mostly) portable public-domain implementation -- D A Gwyn - - last edit: 86/05/30 rms - include config.h, since on VMS it renames some symbols. - Use xmalloc instead of malloc. - - 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 - -#include "config.h" -#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 */ - -#ifdef X3J11 -typedef void *pointer; /* generic pointer type */ -#else -typedef char *pointer; /* generic pointer type */ -#endif /* X3J11 */ - -#define NULL 0 /* null pointer constant */ - -extern void free(); -extern pointer xmalloc(); - -/* - 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; - - free ((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 = xmalloc (sizeof (header) + size); - /* 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)); - } -} - |