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/* objalloc.c -- routines to allocate memory for objects

   Copyright 1997 Free Software Foundation, Inc.

   Written by Ian Lance Taylor, Cygnus Solutions.

This program 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.

This program 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 this program; if not, write to the Free Software

Foundation, 59 Temple Place - Suite 330,

Boston, MA 02111-1307, USA.  */

#include "ansidecl.h"

#include "objalloc.h"

/* Get a definition for NULL.  */

#include <stdio.h>

#if VMS

#include <stdlib.h>

#include <unixlib.h>

#else

#ifdef ANSI_PROTOTYPES

/* Get a definition for size_t.  */

#include <stddef.h>

#endif

/* For systems with larger pointers than ints, this must be declared.  */

extern PTR malloc PARAMS ((size_t));

extern void free PARAMS ((PTR));

#endif

/* These routines allocate space for an object.  Freeing allocated

   space may or may not free all more recently allocated space.

   We handle large and small allocation requests differently.  If we

   don't have enough space in the current block, and the allocation

   request is for more than 512 bytes, we simply pass it through to

   malloc.  */

/* The objalloc structure is defined in objalloc.h.  */

/* This structure appears at the start of each chunk.  */

struct objalloc_chunk

{

  /* Next chunk.  */

  struct objalloc_chunk *next;

  /* If this chunk contains large objects, this is the value of

     current_ptr when this chunk was allocated.  If this chunk

     contains small objects, this is NULL.  */

  char *current_ptr;

};

/* The aligned size of objalloc_chunk.  */

#define CHUNK_HEADER_SIZE                                       \

  ((sizeof (struct objalloc_chunk) + OBJALLOC_ALIGN - 1)        \

   &~ (OBJALLOC_ALIGN - 1))

/* We ask for this much memory each time we create a chunk which is to

   hold small objects.  */

#define CHUNK_SIZE (4096 - 32)

/* A request for this amount or more is just passed through to malloc.  */

#define BIG_REQUEST (512)

/* Create an objalloc structure.  */

struct objalloc *

objalloc_create ()

{

  struct objalloc *ret;

  struct objalloc_chunk *chunk;

  ret = (struct objalloc *) malloc (sizeof *ret);

  if (ret == NULL)

    return NULL;

  ret->chunks = (PTR) malloc (CHUNK_SIZE);

  if (ret->chunks == NULL)

    {

      free (ret);

      return NULL;

    }

  chunk = (struct objalloc_chunk *) ret->chunks;

  chunk->next = NULL;

  chunk->current_ptr = NULL;

  ret->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;

  ret->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;

  return ret;

}

/* Allocate space from an objalloc structure.  */

PTR

_objalloc_alloc (o, len)

     struct objalloc *o;

     unsigned long len;

{

  /* We avoid confusion from zero sized objects by always allocating

     at least 1 byte.  */

  if (len == 0)

    len = 1;

  len = (len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);

  if (len <= o->current_space)

    {

      o->current_ptr += len;

      o->current_space -= len;

      return (PTR) (o->current_ptr - len);

    }

  if (len >= BIG_REQUEST)

    {

      char *ret;

      struct objalloc_chunk *chunk;

      ret = (char *) malloc (CHUNK_HEADER_SIZE + len);

      if (ret == NULL)

        return NULL;

      chunk = (struct objalloc_chunk *) ret;

      chunk->next = (struct objalloc_chunk *) o->chunks;

      chunk->current_ptr = o->current_ptr;

      o->chunks = (PTR) chunk;

      return (PTR) (ret + CHUNK_HEADER_SIZE);

    }

  else

    {

      struct objalloc_chunk *chunk;

      chunk = (struct objalloc_chunk *) malloc (CHUNK_SIZE);

      if (chunk == NULL)

        return NULL;

      chunk->next = (struct objalloc_chunk *) o->chunks;

      chunk->current_ptr = NULL;

      o->current_ptr = (char *) chunk + CHUNK_HEADER_SIZE;

      o->current_space = CHUNK_SIZE - CHUNK_HEADER_SIZE;

      o->chunks = (PTR) chunk;

      return objalloc_alloc (o, len);

    }

}

/* Free an entire objalloc structure.  */

void

objalloc_free (o)

     struct objalloc *o;

{

  struct objalloc_chunk *l;

  l = (struct objalloc_chunk *) o->chunks;

  while (l != NULL)

    {

      struct objalloc_chunk *next;

      next = l->next;

      free (l);

      l = next;

    }

  free (o);

}

/* Free a block from an objalloc structure.  This also frees all more

   recently allocated blocks.  */

void

objalloc_free_block (o, block)

     struct objalloc *o;

     PTR block;

{

  struct objalloc_chunk *p, *small;

  char *b = (char *) block;

  /* First set P to the chunk which contains the block we are freeing,

     and set Q to the last small object chunk we see before P.  */

  small = NULL;

  for (p = (struct objalloc_chunk *) o->chunks; p != NULL; p = p->next)

    {

      if (p->current_ptr == NULL)

        {

          if (b > (char *) p && b < (char *) p + CHUNK_SIZE)

            break;

          small = p;

        }

      else

        {

          if (b == (char *) p + CHUNK_HEADER_SIZE)

            break;

        }

    }

  /* If we can't find the chunk, the caller has made a mistake.  */

  if (p == NULL)

    abort ();

  if (p->current_ptr == NULL)

    {

      struct objalloc_chunk *q;

      struct objalloc_chunk *first;

      /* The block is in a chunk containing small objects.  We can

         free every chunk through SMALL, because they have certainly

         been allocated more recently.  After SMALL, we will not see

         any chunks containing small objects; we can free any big

         chunk if the current_ptr is greater than or equal to B.  We

         can then reset the new current_ptr to B.  */

      first = NULL;

      q = (struct objalloc_chunk *) o->chunks;

      while (q != p)

        {

          struct objalloc_chunk *next;

          next = q->next;

          if (small != NULL)

            {

              if (small == q)

                small = NULL;

              free (q);

            }

          else if (q->current_ptr > b)

            free (q);

          else if (first == NULL)

            first = q;

          q = next;

        }

      if (first == NULL)

        first = p;

      o->chunks = (PTR) first;

      /* Now start allocating from this small block again.  */

      o->current_ptr = b;

      o->current_space = ((char *) p + CHUNK_SIZE) - b;

    }

  else

    {

      struct objalloc_chunk *q;

      char *current_ptr;

      /* This block is in a large chunk by itself.  We can free

         everything on the list up to and including this block.  We

         then start allocating from the next chunk containing small

         objects, setting current_ptr from the value stored with the

         large chunk we are freeing.  */

      current_ptr = p->current_ptr;

      p = p->next;

      q = (struct objalloc_chunk *) o->chunks;

      while (q != p)

        {

          struct objalloc_chunk *next;

          next = q->next;

          free (q);

          q = next;

        }

      o->chunks = (PTR) p;

      while (p->current_ptr != NULL)

        p = p->next;

      o->current_ptr = current_ptr;

      o->current_space = ((char *) p + CHUNK_SIZE) - current_ptr;

    }

}