mmalloc/mrealloc.c

   1 /* Change the size of a block allocated by `mmalloc'.
   2    Copyright 1990, 1991 Free Software Foundation
   3                   Written May 1989 by Mike Haertel.
   4
   5 The GNU C Library is free software; you can redistribute it and/or
   6 modify it under the terms of the GNU Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 License, or (at your option) any later version.
   9
  10 The GNU C Library 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 GNU
  13 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18 Boston, MA 02111-1307, USA.
  19
  20    The author may be reached (Email) at the address mike@ai.mit.edu,
  21    or (US mail) as Mike Haertel c/o Free Software Foundation. */
  22
  23 #include <string.h>     /* Prototypes for memcpy, memmove, memset, etc */
  24
  25 #include "mmprivate.h"
  26
  27 /* Resize the given region to the new size, returning a pointer
  28    to the (possibly moved) region.  This is optimized for speed;
  29    some benchmarks seem to indicate that greater compactness is
  30    achieved by unconditionally allocating and copying to a
  31    new region.  This module has incestuous knowledge of the
  32    internals of both mfree and mmalloc. */
  33
  34 PTR
  35 mrealloc (md, ptr, size)
  36   PTR md;
  37   PTR ptr;
  38   size_t size;
  39 {
  40   struct mdesc *mdp;
  41   PTR result;
  42   int type;
  43   size_t block, blocks, oldlimit;
  44
  45   if (size == 0)
  46     {
  47       mfree (md, ptr);
  48       return (mmalloc (md, 0));
  49     }
  50   else if (ptr == NULL)
  51     {
  52       return (mmalloc (md, size));
  53     }
  54
  55   mdp = MD_TO_MDP (md);
  56
  57   if (mdp -> mrealloc_hook != NULL)
  58     {
  59       return ((*mdp -> mrealloc_hook) (md, ptr, size));
  60     }
  61
  62   block = BLOCK (ptr);
  63
  64   type = mdp -> heapinfo[block].busy.type;
  65   switch (type)
  66     {
  67     case 0:
  68       /* Maybe reallocate a large block to a small fragment.  */
  69       if (size <= BLOCKSIZE / 2)
  70         {
  71           result = mmalloc (md, size);
  72           if (result != NULL)
  73             {
  74               memcpy (result, ptr, size);
  75               mfree (md, ptr);
  76               return (result);
  77             }
  78         }
  79
  80       /* The new size is a large allocation as well;
  81          see if we can hold it in place. */
  82       blocks = BLOCKIFY (size);
  83       if (blocks < mdp -> heapinfo[block].busy.info.size)
  84         {
  85           /* The new size is smaller; return excess memory to the free list. */
  86           mdp -> heapinfo[block + blocks].busy.type = 0;
  87           mdp -> heapinfo[block + blocks].busy.info.size
  88             = mdp -> heapinfo[block].busy.info.size - blocks;
  89           mdp -> heapinfo[block].busy.info.size = blocks;
  90           mfree (md, ADDRESS (block + blocks));
  91           result = ptr;
  92         }
  93       else if (blocks == mdp -> heapinfo[block].busy.info.size)
  94         {
  95           /* No size change necessary.  */
  96           result = ptr;
  97         }
  98       else
  99         {
 100           /* Won't fit, so allocate a new region that will.
 101              Free the old region first in case there is sufficient
 102              adjacent free space to grow without moving. */
 103           blocks = mdp -> heapinfo[block].busy.info.size;
 104           /* Prevent free from actually returning memory to the system.  */
 105           oldlimit = mdp -> heaplimit;
 106           mdp -> heaplimit = 0;
 107           mfree (md, ptr);
 108           mdp -> heaplimit = oldlimit;
 109           result = mmalloc (md, size);
 110           if (result == NULL)
 111             {
 112               mmalloc (md, blocks * BLOCKSIZE);
 113               return (NULL);
 114             }
 115           if (ptr != result)
 116             {
 117               memmove (result, ptr, blocks * BLOCKSIZE);
 118             }
 119         }
 120       break;
 121
 122     default:
 123       /* Old size is a fragment; type is logarithm
 124          to base two of the fragment size.  */
 125       if (size > (size_t) (1 << (type - 1)) && size <= (size_t) (1 << type))
 126         {
 127           /* The new size is the same kind of fragment.  */
 128           result = ptr;
 129         }
 130       else
 131         {
 132           /* The new size is different; allocate a new space,
 133              and copy the lesser of the new size and the old. */
 134           result = mmalloc (md, size);
 135           if (result == NULL)
 136             {
 137               return (NULL);
 138             }
 139           memcpy (result, ptr, MIN (size, (size_t) 1 << type));
 140           mfree (md, ptr);
 141         }
 142       break;
 143     }
 144
 145   return (result);
 146 }
 147
 148 /* When using this package, provide a version of malloc/realloc/free built
 149    on top of it, so that if we use the default sbrk() region we will not
 150    collide with another malloc package trying to do the same thing, if
 151    the application contains any "hidden" calls to malloc/realloc/free (such
 152    as inside a system library). */
 153
 154 PTR
 155 realloc (ptr, size)
 156   PTR ptr;
 157   size_t size;
 158 {
 159   PTR result;
 160
 161   result = mrealloc ((PTR) NULL, ptr, size);
 162   return (result);
 163 }