alloc.c

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

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
the Free Software Foundation; either version 2, or (at your option)
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
the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

#include <config.h>
#include <stdio.h>

/* Note that this declares bzero on OSF/1.  How dumb.  */

#include <signal.h>

/* 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.  */

#undef HIDE_LISP_IMPLEMENTATION
#include "lisp.h"
#include "intervals.h"
#include "puresize.h"
#include "buffer.h"
#include "window.h"
#include "frame.h"
#include "blockinput.h"
#include "keyboard.h"
#include "charset.h"
#include "syssignal.h"
#include <setjmp.h>

extern char *sbrk ();

#ifdef DOUG_LEA_MALLOC

#include <malloc.h>
#define __malloc_size_t int

/* Specify maximum number of areas to mmap.  It would be nice to use a
   value that explicitly means "no limit".  */

#define MMAP_MAX_AREAS 100000000

#else /* not DOUG_LEA_MALLOC */

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

#if defined (STDC_HEADERS)
#include <stddef.h>
#define	__malloc_size_t		size_t
#else
#define	__malloc_size_t		unsigned int
#endif
extern __malloc_size_t _bytes_used;
extern int __malloc_extra_blocks;

#endif /* not DOUG_LEA_MALLOC */

#define max(A,B) ((A) > (B) ? (A) : (B))
#define min(A,B) ((A) < (B) ? (A) : (B))

/* 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.  */

#define VALIDATE_LISP_STORAGE(address, size)			\
do								\
  {								\
    Lisp_Object val;						\
    XSETCONS (val, (char *) address + size);		\
    if ((char *) XCONS (val) != (char *) address + size)	\
      {								\
	xfree (address);					\
	memory_full ();						\
      }								\
  } while (0)

/* Value of _bytes_used, when spare_memory was freed.  */

static __malloc_size_t bytes_used_when_full;

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

#define MARK_STRING(S)		XMARK ((S)->size)
#define UNMARK_STRING(S)	XUNMARK ((S)->size)
#define STRING_MARKED_P(S)	XMARKBIT ((S)->size)

/* 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.  */

int consing_since_gc;

/* Count the amount of consing of various sorts of space.  */

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;
int strings_consed;

/* Number of bytes of consing since GC before another GC should be done. */

int gc_cons_threshold;

/* Nonzero during GC.  */

int gc_in_progress;

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

int garbage_collection_messages;

#ifndef VIRT_ADDR_VARIES
extern
#endif /* VIRT_ADDR_VARIES */
int malloc_sbrk_used;

#ifndef VIRT_ADDR_VARIES
extern
#endif /* VIRT_ADDR_VARIES */
int malloc_sbrk_unused;

/* Two limits controlling how much undo information to keep.  */

int undo_limit;
int undo_strong_limit;

/* 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;

/* Points to memory space allocated as "spare", to be freed if we run
   out of memory.  */

static char *spare_memory;

/* Amount of spare memory to keep in reserve.  */

#define SPARE_MEMORY (1 << 14)

/* Number of extra blocks malloc should get when it needs more core.  */

static int malloc_hysteresis;

/* Nonzero when malloc is called for allocating Lisp object space.
   Currently set but not used.  */

int allocating_for_lisp;

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

Lisp_Object Vpurify_flag;

#ifndef HAVE_SHM

/* Force it into data space! */

EMACS_INT pure[PURESIZE / sizeof (EMACS_INT)] = {0,};
#define PUREBEG (char *) pure

#else /* not HAVE_SHM */

#define pure PURE_SEG_BITS   /* Use shared memory segment */
#define PUREBEG (char *)PURE_SEG_BITS

/* This variable is used only by the XPNTR macro when HAVE_SHM is
   defined.  If we used the PURESIZE macro directly there, that would
   make most of Emacs dependent on puresize.h, which we don't want -
   you should be able to change that without too much recompilation.
   So map_in_data initializes pure_size, and the dependencies work
   out.  */

EMACS_INT pure_size;

#endif /* not HAVE_SHM */

/* 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))

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

int pureptr;

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

char *pending_malloc_warning;

/* Pre-computed signal argument for use when memory is exhausted.  */

Lisp_Object memory_signal_data;

/* 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;

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

int ignore_warnings;

Lisp_Object Qgc_cons_threshold, Qchar_table_extra_slots;

static void mark_buffer P_ ((Lisp_Object));
static void mark_kboards P_ ((void));
static void gc_sweep P_ ((void));
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 */

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));

extern int message_enable_multibyte;

/* 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
};

#if GC_MARK_STACK

#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;

struct mem_node;
static void *lisp_malloc P_ ((int, enum mem_type));
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 *));
static void mark_maybe_object P_ ((Lisp_Object));
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

#endif /* GC_MARK_STACK != 0 */

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

/* Write STR to Vstandard_output plus some advice on how to free some
   memory.  Called when memory gets low.  */

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;
}


/* Function malloc calls this if it finds we are near exhausting
   storage.  */

void
malloc_warning (str)
     char *str;
{
  pending_malloc_warning = str;
}


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

void
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);
}


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


/* Called if malloc returns zero.  */

void
memory_full ()
{
#ifndef SYSTEM_MALLOC
  bytes_used_when_full = BYTES_USED;
#endif

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

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


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

void
buffer_memory_full ()
{
  /* 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.  */

#ifndef REL_ALLOC
  memory_full ();
#endif

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


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

long *
xmalloc (size)
     int size;
{
  register long *val;

  BLOCK_INPUT;
  val = (long *) malloc (size);
  UNBLOCK_INPUT;

  if (!val && size)
    memory_full ();
  return val;
}


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

long *
xrealloc (block, size)
     long *block;
     int size;
{
  register long *val;

  BLOCK_INPUT;
  /* We must call malloc explicitly when BLOCK is 0, since some
     reallocs don't do this.  */
  if (! block)
    val = (long *) malloc (size);
  else
    val = (long *) realloc (block, size);
  UNBLOCK_INPUT;

  if (!val && size) memory_full ();
  return val;
}


/* Like free but block interrupt input..  */

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


/* 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, ...).  */

static void *
lisp_malloc (nbytes, type)
     int nbytes;
     enum mem_type type;
{
  register void *val;

  BLOCK_INPUT;
  allocating_for_lisp++;
  val = (void *) malloc (nbytes);
  allocating_for_lisp--;
  UNBLOCK_INPUT;

  if (!val && nbytes)
    memory_full ();
  
#if GC_MARK_STACK
  if (type != MEM_TYPE_NON_LISP)
    mem_insert (val, (char *) val + nbytes, type);
#endif
  
  return val;
}


/* 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.  */

void
lisp_free (block)
     long *block;
{
  BLOCK_INPUT;
  allocating_for_lisp++;
  free (block);
#if GC_MARK_STACK
  mem_delete (mem_find (block));
#endif
  allocating_for_lisp--;
  UNBLOCK_INPUT;
}


/* 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

extern void * (*__malloc_hook) ();
static void * (*old_malloc_hook) ();
extern void * (*__realloc_hook) ();
static void * (*old_realloc_hook) ();
extern void (*__free_hook) ();
static void (*old_free_hook) ();

/* This function is used as the hook for free to call.  */

static void
emacs_blocked_free (ptr)
     void *ptr;
{
  BLOCK_INPUT;
  __free_hook = old_free_hook;
  free (ptr);
  /* 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
	  > BYTES_USED + max (malloc_hysteresis, 4) * SPARE_MEMORY))
    spare_memory = (char *) malloc (SPARE_MEMORY);

  __free_hook = emacs_blocked_free;
  UNBLOCK_INPUT;
}


/* 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)
    spare_memory = (char *) malloc (SPARE_MEMORY);
}


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

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

  BLOCK_INPUT;
  __malloc_hook = old_malloc_hook;
#ifdef DOUG_LEA_MALLOC
    mallopt (M_TOP_PAD, malloc_hysteresis * 4096);
#else
    __malloc_extra_blocks = malloc_hysteresis;
#endif
  value = (void *) malloc (size);
  __malloc_hook = emacs_blocked_malloc;
  UNBLOCK_INPUT;

  return value;
}


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

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

  BLOCK_INPUT;
  __realloc_hook = old_realloc_hook;
  value = (void *) realloc (ptr, size);
  __realloc_hook = emacs_blocked_realloc;
  UNBLOCK_INPUT;

  return value;
}


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

void
uninterrupt_malloc ()
{
  if (__free_hook != emacs_blocked_free)
    old_free_hook = __free_hook;
  __free_hook = emacs_blocked_free;

  if (__malloc_hook != emacs_blocked_malloc)
    old_malloc_hook = __malloc_hook;
  __malloc_hook = emacs_blocked_malloc;

  if (__realloc_hook != emacs_blocked_realloc)
    old_realloc_hook = __realloc_hook;
  __realloc_hook = emacs_blocked_realloc;
}

#endif /* not SYSTEM_MALLOC */



/***********************************************************************
			 Interval Allocation
 ***********************************************************************/

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

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

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

struct interval_block
{
  struct interval_block *next;
  struct interval intervals[INTERVAL_BLOCK_SIZE];
};

/* Current interval block.  Its `next' pointer points to older
   blocks.  */

struct interval_block *interval_block;

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

static int interval_block_index;

/* Number of free and live intervals.  */

static int total_free_intervals, total_intervals;

/* List of free intervals.  */

INTERVAL interval_free_list;

/* Total number of interval blocks now in use.  */

int n_interval_blocks;


/* Initialize interval allocation.  */

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


/* Return a new interval.  */

INTERVAL
make_interval ()
{
  INTERVAL val;

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

	  newi = (struct interval_block *) lisp_malloc (sizeof *newi,
							MEM_TYPE_NON_LISP);

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


/* Mark Lisp objects in interval I. */

static void
mark_interval (i, dummy)
     register INTERVAL i;
     Lisp_Object dummy;
{
  if (XMARKBIT (i->plist))
    abort ();
  mark_object (&i->plist);
  XMARK (i->plist);
}


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

static void
mark_interval_tree (tree)
     register INTERVAL tree;
{
  /* 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.  */
  XMARK (tree->up.obj);

  traverse_intervals (tree, 1, 0, mark_interval, Qnil);
}


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

#define MARK_INTERVAL_TREE(i)				\
  do {							\
    if (!NULL_INTERVAL_P (i)				\
	&& ! XMARKBIT (i->up.obj))			\
      mark_interval_tree (i);				\
  } while (0)


/* The oddity in the call to XUNMARK is necessary because XUNMARK
   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))				\
     {							\
       XUNMARK ((i)->up.obj);				\
       (i) = balance_intervals (i);			\
     }							\
  } while (0)



/***********************************************************************
			  String Allocation
 ***********************************************************************/

/* 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.

   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.

   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.

   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.  */

/* Size in bytes of an sblock structure used for small strings.  This
   is 8192 minus malloc overhead.  */

#define SBLOCK_SIZE 8188

/* Strings larger than this are considered large strings.  String data
   for large strings is allocated from individual sblocks.  */

#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
{
  /* Back-pointer to the string this sdata belongs to.  If null, this
     structure is free, and the NBYTES member of the union below
     contains the string's byte size (the same value that STRING_BYTES
     would return if STRING were non-null).  If non-null, STRING_BYTES
     (STRING) is the size of the data, and DATA contains the string's
     contents.  */
  struct Lisp_String *string;

  union
  {
    /* When STRING in non-null.  */
    unsigned char data[1];

    /* When STRING is null.  */
    EMACS_INT nbytes;
  } u;
};

/* Structure describing a block of memory which is sub-allocated to
   obtain string data memory for strings.  Blocks for small strings
   are of fixed size SBLOCK_SIZE.  Blocks for large strings are made
   as large as needed.  */

struct sblock
{
  /* Next in list.  */
  struct sblock *next;

  /* Pointer to the next free sdata block.  This points past the end
     of the sblock if there isn't any space left in this block.  */
  struct sdata *next_free;

  /* Start of data.  */
  struct sdata first_data;
};

/* Number of Lisp strings in a string_block structure.  The 1020 is
   1024 minus malloc overhead.  */

#define STRINGS_IN_STRING_BLOCK \
  ((1020 - sizeof (struct string_block *)) / sizeof (struct Lisp_String))

/* Structure describing a block from which Lisp_String structures
   are allocated.  */

struct string_block
{
  struct string_block *next;
  struct Lisp_String strings[STRINGS_IN_STRING_BLOCK];
};

/* Head and tail of the list of sblock structures holding Lisp string
   data.  We always allocate from current_sblock.  The NEXT pointers
   in the sblock structures go from oldest_sblock to current_sblock.  */

static struct sblock *oldest_sblock, *current_sblock;

/* List of sblocks for large strings.  */

static struct sblock *large_sblocks;

/* List of string_block structures, and how many there are.  */

static struct string_block *string_blocks;
static int n_string_blocks;

/* Free-list of Lisp_Strings.  */

static struct Lisp_String *string_free_list;

/* Number of live and free Lisp_Strings.  */

static int total_strings, total_free_strings;

/* Number of bytes used by live strings.  */

static int total_string_size;

/* Given a pointer to a Lisp_String S which is on the free-list
   string_free_list, return a pointer to its successor in the
   free-list.  */

#define NEXT_FREE_LISP_STRING(S) (*(struct Lisp_String **) (S))

/* Return a pointer to the sdata structure belonging to Lisp string S.
   S must be live, i.e. S->data must not be null.  S->data is actually
   a pointer to the `u.data' member of its sdata structure; the
   structure starts at a constant offset in front of that.  */
   
#define SDATA_OF_STRING(S) \
     ((struct sdata *) ((S)->data - sizeof (struct Lisp_String *)))

/* Value is the size of an sdata structure large enough to hold NBYTES
   bytes of string data.  The value returned includes a terminating
   NUL byte, the size of the sdata structure, and padding.  */

#define SDATA_SIZE(NBYTES)			\
     ((sizeof (struct Lisp_String *)		\
       + (NBYTES) + 1				\
       + sizeof (EMACS_INT) - 1)		\
      & ~(sizeof (EMACS_INT) - 1))


/* Initialize string allocation.  Called from init_alloc_once.  */

void
init_strings ()
{
  total_strings = total_free_strings = total_string_size = 0;
  oldest_sblock = current_sblock = large_sblocks = NULL;
  string_blocks = NULL;
  n_string_blocks = 0;
  string_free_list = NULL;
}


/* Return a new Lisp_String.  */

static struct Lisp_String *
allocate_string ()
{
  struct Lisp_String *s;

  /* If the free-list is empty, allocate a new string_block, and
     add all the Lisp_Strings in it to the free-list.  */
  if (string_free_list == NULL)
    {
      struct string_block *b;
      int i;

      b = (struct string_block *) lisp_malloc (sizeof *b, MEM_TYPE_STRING);
      VALIDATE_LISP_STORAGE (b, sizeof *b);
      bzero (b, sizeof *b);
      b->next = string_blocks;
      string_blocks = b;
      ++n_string_blocks;

      for (i = STRINGS_IN_STRING_BLOCK - 1; i >= 0; --i)
	{
	  s = b->strings + i;
	  NEXT_FREE_LISP_STRING (s) = string_free_list;
	  string_free_list = s;
	}

      total_free_strings += STRINGS_IN_STRING_BLOCK;
    }

  /* Pop a Lisp_String off the free-list.  */
  s = string_free_list;
  string_free_list = NEXT_FREE_LISP_STRING (s);

  /* Probably not strictly necessary, but play it safe.  */
  bzero (s, sizeof *s);

  --total_free_strings;
  ++total_strings;
  ++strings_consed;
  consing_since_gc += sizeof *s;

  return s;
}


/* Set up Lisp_String S for holding NCHARS characters, NBYTES bytes,
   plus a NUL byte at the end.  Allocate an sdata structure for S, and
   set S->data to its `u.data' member.  Store a NUL byte at the end of
   S->data.  Set S->size to NCHARS and S->size_byte to NBYTES.  Free
   S->data if it was initially non-null.  */

void
allocate_string_data (s, nchars, nbytes)
     struct Lisp_String *s;
     int nchars, nbytes;
{
  struct sdata *data;
  struct sblock *b;
  int needed;

  /* Determine the number of bytes needed to store NBYTES bytes
     of string data.  */
  needed = SDATA_SIZE (nbytes);