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Diffstat (limited to 'gnu/usr.bin/cvs/lib/alloca.c')
| -rw-r--r-- | gnu/usr.bin/cvs/lib/alloca.c | 191 |
1 files changed, 191 insertions, 0 deletions
diff --git a/gnu/usr.bin/cvs/lib/alloca.c b/gnu/usr.bin/cvs/lib/alloca.c new file mode 100644 index 00000000000..b57659e418c --- /dev/null +++ b/gnu/usr.bin/cvs/lib/alloca.c @@ -0,0 +1,191 @@ +/* + 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 + +#if defined(emacs) || defined(HAVE_CONFIG_H) +#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 || HAVE_CONFIG_H*/ + +#if __STDC__ +typedef void *pointer; /* generic pointer type */ +#else +typedef char *pointer; /* generic pointer type */ +#endif + +#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)); + } +} + |