lib/extendbuf.c

   1 /* extendbuf.c -- manage a dynamically-allocated buffer
   2
   3    Copyright 2004 Free Software Foundation, Inc.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2, or (at your option)
   8    any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, write to the Free Software Foundation,
  17    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  18
  19 /* Written by James Yougnman <jay@gnu.org>. */
  20
  21 #if HAVE_CONFIG_H
  22 # include <config.h>
  23 #endif
  24
  25 #include <stddef.h>
  26 #include <stdlib.h>
  27 #include <assert.h>
  28
  29 #include "xalloc.h"
  30 #include "extendbuf.h"
  31
  32
  33 /* We initially use a small default size to ensure that this code
  34  * gets exercised.
  35  */
  36 #ifndef SIZE_DEFAULT
  37 # define SIZE_DEFAULT 16
  38 #endif
  39
  40 static size_t
  41 decide_size(size_t current, size_t wanted)
  42 {
  43   size_t newsize;
  44
  45   if (0 == current)
  46     newsize = SIZE_DEFAULT;
  47   else
  48     newsize = current;
  49
  50   while (newsize < wanted)
  51     {
  52       if (2 * newsize < newsize)
  53         xalloc_die ();
  54       newsize *= 2;
  55     }
  56   return newsize;
  57 }
  58
  59
  60 void *
  61 extendbuf(void* existing, size_t wanted, size_t *allocated)
  62 {
  63   size_t newsize;
  64
  65   assert(wanted > 0u);
  66   newsize = decide_size(*allocated, wanted);
  67
  68   if ( (*allocated) == 0 )
  69     {
  70       /* Sanity check: If there is no existing allocation size, three
  71        * must be no existing allocated buffer.
  72        */
  73       assert(NULL == existing);
  74
  75       (*allocated) = newsize;
  76       return xmalloc(newsize);
  77     }
  78   else
  79     {
  80       if (newsize != (*allocated) )
  81         {
  82           (*allocated) = newsize;
  83           return xrealloc (existing, newsize);
  84         }
  85       else
  86         {
  87           return existing;
  88         }
  89     }
  90 }