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/* Storage allocation and gc for GNU Emacs Lisp interpreter.
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   Copyright (C) 1985, 86, 88, 93, 94, 95, 97, 98, 1999, 2000, 2001
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      Free Software Foundation, Inc.
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This file is part of GNU Emacs.

GNU Emacs is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs; see the file COPYING.  If not, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */
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#include <config.h>
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#include <stdio.h>
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/* Note that this declares bzero on OSF/1.  How dumb.  */
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#include <signal.h>
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/* GC_MALLOC_CHECK defined means perform validity checks of malloc'd
   memory.  Can do this only if using gmalloc.c.  */

#if defined SYSTEM_MALLOC || defined DOUG_LEA_MALLOC
#undef GC_MALLOC_CHECK
#endif

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/* This file is part of the core Lisp implementation, and thus must
   deal with the real data structures.  If the Lisp implementation is
   replaced, this file likely will not be used.  */
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#undef HIDE_LISP_IMPLEMENTATION
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#include "lisp.h"
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#include "intervals.h"
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#include "puresize.h"
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#include "buffer.h"
#include "window.h"
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#include "keyboard.h"
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#include "frame.h"
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#include "blockinput.h"
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#include "charset.h"
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#include "syssignal.h"
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#include <setjmp.h>
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#ifdef HAVE_UNISTD_H
#include <unistd.h>
#else
extern POINTER_TYPE *sbrk ();
#endif
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#ifdef DOUG_LEA_MALLOC
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#include <malloc.h>
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/* malloc.h #defines this as size_t, at least in glibc2.  */
#ifndef __malloc_size_t
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#define __malloc_size_t int
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#endif
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/* Specify maximum number of areas to mmap.  It would be nice to use a
   value that explicitly means "no limit".  */

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#define MMAP_MAX_AREAS 100000000

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#else /* not DOUG_LEA_MALLOC */

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/* The following come from gmalloc.c.  */

#define	__malloc_size_t		size_t
extern __malloc_size_t _bytes_used;
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extern __malloc_size_t __malloc_extra_blocks;
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#endif /* not DOUG_LEA_MALLOC */
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#define max(A,B) ((A) > (B) ? (A) : (B))
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#define min(A,B) ((A) < (B) ? (A) : (B))
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/* Macro to verify that storage intended for Lisp objects is not
   out of range to fit in the space for a pointer.
   ADDRESS is the start of the block, and SIZE
   is the amount of space within which objects can start.  */
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#define VALIDATE_LISP_STORAGE(address, size)			\
do								\
  {								\
    Lisp_Object val;						\
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    XSETCONS (val, (char *) address + size);		\
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    if ((char *) XCONS (val) != (char *) address + size)	\
      {								\
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	xfree (address);					\
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	memory_full ();						\
      }								\
  } while (0)

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/* Value of _bytes_used, when spare_memory was freed.  */
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static __malloc_size_t bytes_used_when_full;

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/* Mark, unmark, query mark bit of a Lisp string.  S must be a pointer
   to a struct Lisp_String.  */

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#define MARK_STRING(S)		((S)->size |= MARKBIT)
#define UNMARK_STRING(S)	((S)->size &= ~MARKBIT)
#define STRING_MARKED_P(S)	((S)->size & MARKBIT)
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/* Value is the number of bytes/chars of S, a pointer to a struct
   Lisp_String.  This must be used instead of STRING_BYTES (S) or
   S->size during GC, because S->size contains the mark bit for
   strings.  */

#define GC_STRING_BYTES(S)	(STRING_BYTES (S) & ~MARKBIT)
#define GC_STRING_CHARS(S)	((S)->size & ~MARKBIT)

/* Number of bytes of consing done since the last gc.  */

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int consing_since_gc;

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/* Count the amount of consing of various sorts of space.  */
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int cons_cells_consed;
int floats_consed;
int vector_cells_consed;
int symbols_consed;
int string_chars_consed;
int misc_objects_consed;
int intervals_consed;
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int strings_consed;

/* Number of bytes of consing since GC before another GC should be done. */
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int gc_cons_threshold;
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/* Nonzero during GC.  */

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int gc_in_progress;

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/* Nonzero means display messages at beginning and end of GC.  */
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int garbage_collection_messages;

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#ifndef VIRT_ADDR_VARIES
extern
#endif /* VIRT_ADDR_VARIES */
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int malloc_sbrk_used;
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#ifndef VIRT_ADDR_VARIES
extern
#endif /* VIRT_ADDR_VARIES */
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int malloc_sbrk_unused;
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/* Two limits controlling how much undo information to keep.  */
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int undo_limit;
int undo_strong_limit;
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/* Number of live and free conses etc.  */

static int total_conses, total_markers, total_symbols, total_vector_size;
static int total_free_conses, total_free_markers, total_free_symbols;
static int total_free_floats, total_floats;
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/* Points to memory space allocated as "spare", to be freed if we run
   out of memory.  */

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static char *spare_memory;

/* Amount of spare memory to keep in reserve.  */
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#define SPARE_MEMORY (1 << 14)

/* Number of extra blocks malloc should get when it needs more core.  */
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static int malloc_hysteresis;

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/* Non-nil means defun should do purecopy on the function definition.  */

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Lisp_Object Vpurify_flag;

#ifndef HAVE_SHM
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/* Force it into data space! */

EMACS_INT pure[PURESIZE / sizeof (EMACS_INT)] = {0,};
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#define PUREBEG (char *) pure
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#else /* not HAVE_SHM */

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#define pure PURE_SEG_BITS   /* Use shared memory segment */
#define PUREBEG (char *)PURE_SEG_BITS
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/* This variable is used only by the XPNTR macro when HAVE_SHM is
   defined.  If we used the PURESIZE macro directly there, that would
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   make most of Emacs dependent on puresize.h, which we don't want -
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   you should be able to change that without too much recompilation.
   So map_in_data initializes pure_size, and the dependencies work
   out.  */
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EMACS_INT pure_size;
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#endif /* not HAVE_SHM */

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/* Value is non-zero if P points into pure space.  */

#define PURE_POINTER_P(P)					\
     (((PNTR_COMPARISON_TYPE) (P)				\
       < (PNTR_COMPARISON_TYPE) ((char *) pure + PURESIZE))	\
      && ((PNTR_COMPARISON_TYPE) (P)				\
	  >= (PNTR_COMPARISON_TYPE) pure))

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/* Index in pure at which next pure object will be allocated.. */

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int pure_bytes_used;
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/* If nonzero, this is a warning delivered by malloc and not yet
   displayed.  */

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char *pending_malloc_warning;

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/* Pre-computed signal argument for use when memory is exhausted.  */
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Lisp_Object memory_signal_data;
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/* Maximum amount of C stack to save when a GC happens.  */

#ifndef MAX_SAVE_STACK
#define MAX_SAVE_STACK 16000
#endif

/* Buffer in which we save a copy of the C stack at each GC.  */

char *stack_copy;
int stack_copy_size;

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/* Non-zero means ignore malloc warnings.  Set during initialization.
   Currently not used.  */

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int ignore_warnings;
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Lisp_Object Qgc_cons_threshold, Qchar_table_extra_slots;
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static void mark_buffer P_ ((Lisp_Object));
static void mark_kboards P_ ((void));
static void gc_sweep P_ ((void));
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static void mark_glyph_matrix P_ ((struct glyph_matrix *));
static void mark_face_cache P_ ((struct face_cache *));

#ifdef HAVE_WINDOW_SYSTEM
static void mark_image P_ ((struct image *));
static void mark_image_cache P_ ((struct frame *));
#endif /* HAVE_WINDOW_SYSTEM */

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static struct Lisp_String *allocate_string P_ ((void));
static void compact_small_strings P_ ((void));
static void free_large_strings P_ ((void));
static void sweep_strings P_ ((void));
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extern int message_enable_multibyte;
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/* When scanning the C stack for live Lisp objects, Emacs keeps track
   of what memory allocated via lisp_malloc is intended for what
   purpose.  This enumeration specifies the type of memory.  */

enum mem_type
{
  MEM_TYPE_NON_LISP,
  MEM_TYPE_BUFFER,
  MEM_TYPE_CONS,
  MEM_TYPE_STRING,
  MEM_TYPE_MISC,
  MEM_TYPE_SYMBOL,
  MEM_TYPE_FLOAT,
  MEM_TYPE_VECTOR
};

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#if GC_MARK_STACK || defined GC_MALLOC_CHECK
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#if GC_MARK_STACK == GC_USE_GCPROS_CHECK_ZOMBIES
#include <stdio.h>		/* For fprintf.  */
#endif

/* A unique object in pure space used to make some Lisp objects
   on free lists recognizable in O(1).  */

Lisp_Object Vdead;

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#ifdef GC_MALLOC_CHECK

enum mem_type allocated_mem_type;
int dont_register_blocks;

#endif /* GC_MALLOC_CHECK */

/* A node in the red-black tree describing allocated memory containing
   Lisp data.  Each such block is recorded with its start and end
   address when it is allocated, and removed from the tree when it
   is freed.

   A red-black tree is a balanced binary tree with the following
   properties:

   1. Every node is either red or black.
   2. Every leaf is black.
   3. If a node is red, then both of its children are black.
   4. Every simple path from a node to a descendant leaf contains
   the same number of black nodes.
   5. The root is always black.

   When nodes are inserted into the tree, or deleted from the tree,
   the tree is "fixed" so that these properties are always true.

   A red-black tree with N internal nodes has height at most 2
   log(N+1).  Searches, insertions and deletions are done in O(log N).
   Please see a text book about data structures for a detailed
   description of red-black trees.  Any book worth its salt should
   describe them.  */

struct mem_node
{
  struct mem_node *left, *right, *parent;

  /* Start and end of allocated region.  */
  void *start, *end;

  /* Node color.  */
  enum {MEM_BLACK, MEM_RED} color;
  
  /* Memory type.  */
  enum mem_type type;
};

/* Base address of stack.  Set in main.  */

Lisp_Object *stack_base;

/* Root of the tree describing allocated Lisp memory.  */

static struct mem_node *mem_root;

/* Sentinel node of the tree.  */

static struct mem_node mem_z;
#define MEM_NIL &mem_z

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static POINTER_TYPE *lisp_malloc P_ ((size_t, enum mem_type));
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static void lisp_free P_ ((POINTER_TYPE *));
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static void mark_stack P_ ((void));
static void init_stack P_ ((Lisp_Object *));
static int live_vector_p P_ ((struct mem_node *, void *));
static int live_buffer_p P_ ((struct mem_node *, void *));
static int live_string_p P_ ((struct mem_node *, void *));
static int live_cons_p P_ ((struct mem_node *, void *));
static int live_symbol_p P_ ((struct mem_node *, void *));
static int live_float_p P_ ((struct mem_node *, void *));
static int live_misc_p P_ ((struct mem_node *, void *));
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static void mark_maybe_object P_ ((Lisp_Object));
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static void mark_memory P_ ((void *, void *));
static void mem_init P_ ((void));
static struct mem_node *mem_insert P_ ((void *, void *, enum mem_type));
static void mem_insert_fixup P_ ((struct mem_node *));
static void mem_rotate_left P_ ((struct mem_node *));
static void mem_rotate_right P_ ((struct mem_node *));
static void mem_delete P_ ((struct mem_node *));
static void mem_delete_fixup P_ ((struct mem_node *));
static INLINE struct mem_node *mem_find P_ ((void *));

#if GC_MARK_STACK == GC_MARK_STACK_CHECK_GCPROS
static void check_gcpros P_ ((void));
#endif

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#endif /* GC_MARK_STACK || GC_MALLOC_CHECK */
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/* Recording what needs to be marked for gc.  */

struct gcpro *gcprolist;

/* Addresses of staticpro'd variables.  */

#define NSTATICS 1024
Lisp_Object *staticvec[NSTATICS] = {0};

/* Index of next unused slot in staticvec.  */

int staticidx = 0;

static POINTER_TYPE *pure_alloc P_ ((size_t, int));


/* Value is SZ rounded up to the next multiple of ALIGNMENT.
   ALIGNMENT must be a power of 2.  */

#define ALIGN(SZ, ALIGNMENT) \
  (((SZ) + (ALIGNMENT) - 1) & ~((ALIGNMENT) - 1))

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/************************************************************************
				Malloc
 ************************************************************************/

/* Write STR to Vstandard_output plus some advice on how to free some
   memory.  Called when memory gets low.  */
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Lisp_Object
malloc_warning_1 (str)
     Lisp_Object str;
{
  Fprinc (str, Vstandard_output);
  write_string ("\nKilling some buffers may delay running out of memory.\n", -1);
  write_string ("However, certainly by the time you receive the 95% warning,\n", -1);
  write_string ("you should clean up, kill this Emacs, and start a new one.", -1);
  return Qnil;
}

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/* Function malloc calls this if it finds we are near exhausting
   storage.  */
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void
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malloc_warning (str)
     char *str;
{
  pending_malloc_warning = str;
}

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/* Display a malloc warning in buffer *Danger*.  */

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void
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display_malloc_warning ()
{
  register Lisp_Object val;

  val = build_string (pending_malloc_warning);
  pending_malloc_warning = 0;
  internal_with_output_to_temp_buffer (" *Danger*", malloc_warning_1, val);
}

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#ifdef DOUG_LEA_MALLOC
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#  define BYTES_USED (mallinfo ().arena)
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#else
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#  define BYTES_USED _bytes_used
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#endif

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/* Called if malloc returns zero.  */
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void
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memory_full ()
{
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#ifndef SYSTEM_MALLOC
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  bytes_used_when_full = BYTES_USED;
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#endif

  /* The first time we get here, free the spare memory.  */
  if (spare_memory)
    {
      free (spare_memory);
      spare_memory = 0;
    }

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  /* This used to call error, but if we've run out of memory, we could
     get infinite recursion trying to build the string.  */
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  while (1)
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    Fsignal (Qnil, memory_signal_data);
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}

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/* Called if we can't allocate relocatable space for a buffer.  */

void
buffer_memory_full ()
{
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  /* If buffers use the relocating allocator, no need to free
     spare_memory, because we may have plenty of malloc space left
     that we could get, and if we don't, the malloc that fails will
     itself cause spare_memory to be freed.  If buffers don't use the
     relocating allocator, treat this like any other failing
     malloc.  */
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#ifndef REL_ALLOC
  memory_full ();
#endif

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  /* This used to call error, but if we've run out of memory, we could
     get infinite recursion trying to build the string.  */
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  while (1)
    Fsignal (Qerror, memory_signal_data);
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}

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/* Like malloc but check for no memory and block interrupt input..  */
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POINTER_TYPE *
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xmalloc (size)
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     size_t size;
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{
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  register POINTER_TYPE *val;
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  BLOCK_INPUT;
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  val = (POINTER_TYPE *) malloc (size);
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  UNBLOCK_INPUT;
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  if (!val && size)
    memory_full ();
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  return val;
}

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/* Like realloc but check for no memory and block interrupt input..  */

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POINTER_TYPE *
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xrealloc (block, size)
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     POINTER_TYPE *block;
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     size_t size;
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{
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  register POINTER_TYPE *val;
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  BLOCK_INPUT;
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  /* We must call malloc explicitly when BLOCK is 0, since some
     reallocs don't do this.  */
  if (! block)
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    val = (POINTER_TYPE *) malloc (size);
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  else
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    val = (POINTER_TYPE *) realloc (block, size);
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  UNBLOCK_INPUT;
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  if (!val && size) memory_full ();
  return val;
}
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/* Like free but block interrupt input..  */

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void
xfree (block)
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     POINTER_TYPE *block;
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{
  BLOCK_INPUT;
  free (block);
  UNBLOCK_INPUT;
}

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/* Like strdup, but uses xmalloc.  */

char *
xstrdup (s)
     char *s;
{
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  size_t len = strlen (s) + 1;
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  char *p = (char *) xmalloc (len);
  bcopy (s, p, len);
  return p;
}


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/* Like malloc but used for allocating Lisp data.  NBYTES is the
   number of bytes to allocate, TYPE describes the intended use of the
   allcated memory block (for strings, for conses, ...).  */

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static POINTER_TYPE *
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lisp_malloc (nbytes, type)
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     size_t nbytes;
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     enum mem_type type;
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{
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  register void *val;
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  BLOCK_INPUT;
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#ifdef GC_MALLOC_CHECK
  allocated_mem_type = type;
#endif
  
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  val = (void *) malloc (nbytes);
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#if GC_MARK_STACK && !defined GC_MALLOC_CHECK
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  if (val && type != MEM_TYPE_NON_LISP)
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    mem_insert (val, (char *) val + nbytes, type);
#endif
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  UNBLOCK_INPUT;
  if (!val && nbytes)
    memory_full ();
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  return val;
}

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/* Return a new buffer structure allocated from the heap with
   a call to lisp_malloc.  */

struct buffer *
allocate_buffer ()
{
  return (struct buffer *) lisp_malloc (sizeof (struct buffer),
					MEM_TYPE_BUFFER);
}


/* Free BLOCK.  This must be called to free memory allocated with a
   call to lisp_malloc.  */

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static void
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lisp_free (block)
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     POINTER_TYPE *block;
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{
  BLOCK_INPUT;
  free (block);
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#if GC_MARK_STACK && !defined GC_MALLOC_CHECK
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  mem_delete (mem_find (block));
#endif
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  UNBLOCK_INPUT;
}
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/* Arranging to disable input signals while we're in malloc.

   This only works with GNU malloc.  To help out systems which can't
   use GNU malloc, all the calls to malloc, realloc, and free
   elsewhere in the code should be inside a BLOCK_INPUT/UNBLOCK_INPUT
   pairs; unfortunately, we have no idea what C library functions
   might call malloc, so we can't really protect them unless you're
   using GNU malloc.  Fortunately, most of the major operating can use
   GNU malloc.  */

#ifndef SYSTEM_MALLOC
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#ifndef DOUG_LEA_MALLOC
extern void * (*__malloc_hook) P_ ((size_t));
extern void * (*__realloc_hook) P_ ((void *, size_t));
extern void (*__free_hook) P_ ((void *));
/* Else declared in malloc.h, perhaps with an extra arg.  */
#endif /* DOUG_LEA_MALLOC */
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static void * (*old_malloc_hook) ();
static void * (*old_realloc_hook) ();
static void (*old_free_hook) ();
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/* This function is used as the hook for free to call.  */

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static void
emacs_blocked_free (ptr)
     void *ptr;
{
  BLOCK_INPUT;
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#ifdef GC_MALLOC_CHECK
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  if (ptr)
    {
      struct mem_node *m;
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      m = mem_find (ptr);
      if (m == MEM_NIL || m->start != ptr)
	{
	  fprintf (stderr,
		   "Freeing `%p' which wasn't allocated with malloc\n", ptr);
	  abort ();
	}
      else
	{
	  /* fprintf (stderr, "free %p...%p (%p)\n", m->start, m->end, ptr); */
	  mem_delete (m);
	}
    }
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#endif /* GC_MALLOC_CHECK */
  
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  __free_hook = old_free_hook;
  free (ptr);
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  /* If we released our reserve (due to running out of memory),
     and we have a fair amount free once again,
     try to set aside another reserve in case we run out once more.  */
  if (spare_memory == 0
      /* Verify there is enough space that even with the malloc
	 hysteresis this call won't run out again.
	 The code here is correct as long as SPARE_MEMORY
	 is substantially larger than the block size malloc uses.  */
      && (bytes_used_when_full
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	  > BYTES_USED + max (malloc_hysteresis, 4) * SPARE_MEMORY))
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    spare_memory = (char *) malloc ((size_t) SPARE_MEMORY);
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  __free_hook = emacs_blocked_free;
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  UNBLOCK_INPUT;
}

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/* If we released our reserve (due to running out of memory),
   and we have a fair amount free once again,
   try to set aside another reserve in case we run out once more.

   This is called when a relocatable block is freed in ralloc.c.  */

void
refill_memory_reserve ()
{
  if (spare_memory == 0)
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    spare_memory = (char *) malloc ((size_t) SPARE_MEMORY);
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}

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/* This function is the malloc hook that Emacs uses.  */

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static void *
emacs_blocked_malloc (size)
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     size_t size;
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{
  void *value;

  BLOCK_INPUT;
  __malloc_hook = old_malloc_hook;
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#ifdef DOUG_LEA_MALLOC
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    mallopt (M_TOP_PAD, malloc_hysteresis * 4096);
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#else
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    __malloc_extra_blocks = malloc_hysteresis;
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#endif
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  value = (void *) malloc (size);
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#ifdef GC_MALLOC_CHECK
  {
    struct mem_node *m = mem_find (value);
    if (m != MEM_NIL)
      {
	fprintf (stderr, "Malloc returned %p which is already in use\n",
		 value);
	fprintf (stderr, "Region in use is %p...%p, %u bytes, type %d\n",
		 m->start, m->end, (char *) m->end - (char *) m->start,
		 m->type);
	abort ();
      }

    if (!dont_register_blocks)
      {
	mem_insert (value, (char *) value + max (1, size), allocated_mem_type);
	allocated_mem_type = MEM_TYPE_NON_LISP;
      }
  }
#endif /* GC_MALLOC_CHECK */
  
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  __malloc_hook = emacs_blocked_malloc;
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  UNBLOCK_INPUT;

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  /* fprintf (stderr, "%p malloc\n", value); */
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  return value;
}

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/* This function is the realloc hook that Emacs uses.  */

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static void *
emacs_blocked_realloc (ptr, size)
     void *ptr;
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     size_t size;
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{
  void *value;

  BLOCK_INPUT;
  __realloc_hook = old_realloc_hook;
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#ifdef GC_MALLOC_CHECK
  if (ptr)
    {
      struct mem_node *m = mem_find (ptr);
      if (m == MEM_NIL || m->start != ptr)
	{
	  fprintf (stderr,
		   "Realloc of %p which wasn't allocated with malloc\n",
		   ptr);
	  abort ();
	}

      mem_delete (m);
    }
  
  /* fprintf (stderr, "%p -> realloc\n", ptr); */
  
  /* Prevent malloc from registering blocks.  */
  dont_register_blocks = 1;
#endif /* GC_MALLOC_CHECK */

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  value = (void *) realloc (ptr, size);
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#ifdef GC_MALLOC_CHECK
  dont_register_blocks = 0;

  {
    struct mem_node *m = mem_find (value);
    if (m != MEM_NIL)
      {
	fprintf (stderr, "Realloc returns memory that is already in use\n");
	abort ();
      }

    /* Can't handle zero size regions in the red-black tree.  */
    mem_insert (value, (char *) value + max (size, 1), MEM_TYPE_NON_LISP);
  }
  
  /* fprintf (stderr, "%p <- realloc\n", value); */
#endif /* GC_MALLOC_CHECK */
  
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  __realloc_hook = emacs_blocked_realloc;
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  UNBLOCK_INPUT;

  return value;
}

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/* Called from main to set up malloc to use our hooks.  */

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void
uninterrupt_malloc ()
{
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  if (__free_hook != emacs_blocked_free)
    old_free_hook = __free_hook;
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  __free_hook = emacs_blocked_free;
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  if (__malloc_hook != emacs_blocked_malloc)
    old_malloc_hook = __malloc_hook;
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  __malloc_hook = emacs_blocked_malloc;
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  if (__realloc_hook != emacs_blocked_realloc)
    old_realloc_hook = __realloc_hook;
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  __realloc_hook = emacs_blocked_realloc;
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}
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#endif /* not SYSTEM_MALLOC */


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833

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/***********************************************************************
			 Interval Allocation
 ***********************************************************************/
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/* Number of intervals allocated in an interval_block structure.
   The 1020 is 1024 minus malloc overhead.  */

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#define INTERVAL_BLOCK_SIZE \
  ((1020 - sizeof (struct interval_block *)) / sizeof (struct interval))

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/* Intervals are allocated in chunks in form of an interval_block
   structure.  */

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struct interval_block
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{
  struct interval_block *next;
  struct interval intervals[INTERVAL_BLOCK_SIZE];
};
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/* Current interval block.  Its `next' pointer points to older
   blocks.  */

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struct interval_block *interval_block;
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/* Index in interval_block above of the next unused interval
   structure.  */

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static int interval_block_index;
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/* Number of free and live intervals.  */

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static int total_free_intervals, total_intervals;
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/* List of free intervals.  */

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INTERVAL interval_free_list;

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/* Total number of interval blocks now in use.  */
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int n_interval_blocks;

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/* Initialize interval allocation.  */

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static void
init_intervals ()
{
  interval_block
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    = (struct interval_block *) lisp_malloc (sizeof *interval_block,
					     MEM_TYPE_NON_LISP);
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  interval_block->next = 0;
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  bzero ((char *) interval_block->intervals, sizeof interval_block->intervals);
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  interval_block_index = 0;
  interval_free_list = 0;
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  n_interval_blocks = 1;
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}

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/* Return a new interval.  */
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INTERVAL
make_interval ()
{
  INTERVAL val;

  if (interval_free_list)
    {
      val = interval_free_list;
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      interval_free_list = INTERVAL_PARENT (interval_free_list);
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    }
  else
    {
      if (interval_block_index == INTERVAL_BLOCK_SIZE)
	{
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	  register struct interval_block *newi;

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	  newi = (struct interval_block *) lisp_malloc (sizeof *newi,
							MEM_TYPE_NON_LISP);
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	  VALIDATE_LISP_STORAGE (newi, sizeof *newi);
	  newi->next = interval_block;
	  interval_block = newi;
	  interval_block_index = 0;
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	  n_interval_blocks++;
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	}
      val = &interval_block->intervals[interval_block_index++];
    }
  consing_since_gc += sizeof (struct interval);
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  intervals_consed++;
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  RESET_INTERVAL (val);
  return val;
}

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/* Mark Lisp objects in interval I. */
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static void
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mark_interval (i, dummy)
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     register INTERVAL i;
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     Lisp_Object dummy;
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{
  if (XMARKBIT (i->plist))
    abort ();
  mark_object (&i->plist);
  XMARK (i->plist);
}

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/* Mark the interval tree rooted in TREE.  Don't call this directly;
   use the macro MARK_INTERVAL_TREE instead.  */

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static void
mark_interval_tree (tree)
     register INTERVAL tree;
{
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  /* No need to test if this tree has been marked already; this
     function is always called through the MARK_INTERVAL_TREE macro,
     which takes care of that.  */

  /* XMARK expands to an assignment; the LHS of an assignment can't be
     a cast.  */
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  XMARK (tree->up.obj);
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  traverse_intervals (tree, 1, 0, mark_interval, Qnil);
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}

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/* Mark the interval tree rooted in I.  */

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#define MARK_INTERVAL_TREE(i)				\
  do {							\
    if (!NULL_INTERVAL_P (i)				\
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	&& ! XMARKBIT (i->up.obj))			\
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      mark_interval_tree (i);				\
  } while (0)
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/* The oddity in the call to XUNMARK is necessary because XUNMARK
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   expands to an assignment to its argument, and most C compilers
   don't support casts on the left operand of `='.  */

#define UNMARK_BALANCE_INTERVALS(i)			\
  do {							\
   if (! NULL_INTERVAL_P (i))				\
     {							\
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       XUNMARK ((i)->up.obj);				\
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       (i) = balance_intervals (i);			\
     }							\
  } while (0)
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/* Number support.  If NO_UNION_TYPE isn't in effect, we
   can't create number objects in macros.  */
#ifndef make_number
Lisp_Object
make_number (n)
     int n;
{
  Lisp_Object obj;
  obj.s.val = n;
  obj.s.type = Lisp_Int;
  return obj;
}
#endif
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/***********************************************************************
			  String Allocation
 ***********************************************************************/
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/* Lisp_Strings are allocated in string_block structures.  When a new
   string_block is allocated, all the Lisp_Strings it contains are
   added to a free-list stiing_free_list.  When a new Lisp_String is
   needed, it is taken from that list.  During the sweep phase of GC,
   string_blocks that are entirely free are freed, except two which
   we keep.
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   String data is allocated from sblock structures.  Strings larger
   than LARGE_STRING_BYTES, get their own sblock, data for smaller
   strings is sub-allocated out of sblocks of size SBLOCK_SIZE.
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   Sblocks consist internally of sdata structures, one for each
   Lisp_String.  The sdata structure points to the Lisp_String it
   belongs to.  The Lisp_String points back to the `u.data' member of
   its sdata structure.
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   When a Lisp_String is freed during GC, it is put back on
   string_free_list, and its `data' member and its sdata's `string'
   pointer is set to null.  The size of the string is recorded in the
   `u.nbytes' member of the sdata.  So, sdata structures that are no
   longer used, can be easily recognized, and it's easy to compact the
   sblocks of small strings which we do in compact_small_strings.  */
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/* Size in bytes of an sblock structure used for small strings.  This
   is 8192 minus malloc overhead.  */
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#define SBLOCK_SIZE 8188
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/* Strings larger than this are considered large strings.  String data
   for large strings is allocated from individual sblocks.  */
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#define LARGE_STRING_BYTES 1024

/* Structure describing string memory sub-allocated from an sblock.
   This is where the contents of Lisp strings are stored.  */

struct sdata
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{
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