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/* 
|| This file is part of Pike. For copyright information see COPYRIGHT. 
|| Pike is distributed under GPL, LGPL and MPL. See the file COPYING 
|| for more information. 
*/ 
 
#include <stdio.h> 
/* 
        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 
 
#ifdef emacs 
#include "global.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 
 
#ifndef NULL 
#define       NULL    0                       /* null pointer constant */ 
#endif 
 
extern void     free(); 
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 = &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 pike_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 = malloc (sizeof (header) + size); 
    /* address of header */ 
    if (!new) { fprintf(stderr,"alloca: failed!"); return NULL; } 
 
    ((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)); 
  } 
}