/* extendbuf.c -- manage a dynamically-allocated buffer

   Copyright 2004 Free Software Foundation, Inc.

   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,
   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* Written by James Yougnman <jay@gnu.org>. */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <stddef.h>
#include <stdlib.h>
#include <assert.h>

#include "xalloc.h"
#include "extendbuf.h"


/* We initially use a small default size to ensure that this code 
 * gets exercised. 
 */
#ifndef SIZE_DEFAULT
# define SIZE_DEFAULT 16
#endif

static size_t
decide_size(size_t current, size_t wanted)
{
  size_t newsize;
  
  if (0 == current)
    newsize = SIZE_DEFAULT;
  else
    newsize = current;
  
  while (newsize < wanted)
    {
      if (2 * newsize < newsize)
	xalloc_die ();
      newsize *= 2;
    }
  return newsize;
}


void *
extendbuf(void* existing, size_t wanted, size_t *allocated)
{
  size_t newsize;
  
  assert(wanted > 0u);
  newsize = decide_size(*allocated, wanted);

  if ( (*allocated) == 0 )
    {
      /* Sanity check: If there is no existing allocation size, three
       * must be no existing allocated buffer.
       */
      assert(NULL == existing);

      (*allocated) = newsize;
      return xmalloc(newsize);
    }
  else
    {
      if (newsize != (*allocated) )
	{
	  (*allocated) = newsize;
	  return xrealloc (existing, newsize);
	}
      else
	{
	  return existing;
	}
    }
}