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., 675 Mass Ave,
  18 Cambridge, MA 02139, 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 "mmalloc.h"
  24
  25 /* Resize the given region to the new size, returning a pointer
  26    to the (possibly moved) region.  This is optimized for speed;
  27    some benchmarks seem to indicate that greater compactness is
  28    achieved by unconditionally allocating and copying to a
  29    new region.  This module has incestuous knowledge of the
  30    internals of both mfree and mmalloc. */
  31
  32 PTR
  33 mrealloc (md, ptr, size)
  34   PTR md;
  35   PTR ptr;
  36   size_t size;
  37 {
  38   struct mdesc *mdp;
  39   PTR result;
  40   int type;
  41   size_t block, blocks, oldlimit;
  42
  43   if (size == 0)
  44     {
  45       mfree (md, ptr);
  46       return (mmalloc (md, 0));
  47     }
  48   else if (ptr == NULL)
  49     return (mmalloc (md, size));
  50
  51   mdp = MD_TO_MDP (md);
  52
  53   if (mdp -> mrealloc_hook != NULL)
  54     {
  55       return ((*mdp -> mrealloc_hook) (md, ptr, size));
  56     }
  57
  58   block = BLOCK(ptr);
  59
  60   type = mdp -> heapinfo[block].busy.type;
  61   switch (type)
  62     {
  63     case 0:
  64       /* Maybe reallocate a large block to a small fragment.  */
  65       if (size <= BLOCKSIZE / 2)
  66         {
  67           result = mmalloc (md, size);
  68           if (result != NULL)
  69             {
  70               memcpy (result, ptr, size);
  71               mfree (md, ptr);
  72               return (result);
  73             }
  74         }
  75
  76       /* The new size is a large allocation as well;
  77          see if we can hold it in place. */
  78       blocks = BLOCKIFY(size);
  79       if (blocks < mdp -> heapinfo[block].busy.info.size)
  80         {
  81           /* The new size is smaller; return
  82              excess memory to the free list. */
  83           mdp -> heapinfo[block + blocks].busy.type = 0;
  84           mdp -> heapinfo[block + blocks].busy.info.size
  85             = mdp -> heapinfo[block].busy.info.size - blocks;
  86           mdp -> heapinfo[block].busy.info.size = blocks;
  87           mfree (md, ADDRESS(block + blocks));
  88           result = ptr;
  89         }
  90       else if (blocks == mdp -> heapinfo[block].busy.info.size)
  91         /* No size change necessary.  */
  92         result = ptr;
  93       else
  94         {
  95           /* Won't fit, so allocate a new region that will.
  96              Free the old region first in case there is sufficient
  97              adjacent free space to grow without moving. */
  98           blocks = mdp -> heapinfo[block].busy.info.size;
  99           /* Prevent free from actually returning memory to the system.  */
 100           oldlimit = mdp -> heaplimit;
 101           mdp -> heaplimit = 0;
 102           mfree (md, ptr);
 103           mdp -> heaplimit = oldlimit;
 104           result = mmalloc (md, size);
 105           if (result == NULL)
 106             {
 107               (void) mmalloc (md, blocks * BLOCKSIZE);
 108               return NULL;
 109             }
 110           if (ptr != result)
 111             memmove (result, ptr, blocks * BLOCKSIZE);
 112         }
 113       break;
 114
 115     default:
 116       /* Old size is a fragment; type is logarithm
 117          to base two of the fragment size.  */
 118       if (size > (size_t) (1 << (type - 1)) && size <= (size_t) (1 << type))
 119         /* The new size is the same kind of fragment.  */
 120         result = ptr;
 121       else
 122         {
 123           /* The new size is different; allocate a new space,
 124              and copy the lesser of the new size and the old. */
 125           result = mmalloc (md, size);
 126           if (result == NULL)
 127             return (NULL);
 128           memcpy (result, ptr, MIN(size, (size_t) 1 << type));
 129           mfree (md, ptr);
 130         }
 131       break;
 132     }
 133
 134   return (result);
 135 }
 136
 137 /* When using this package, provide a version of malloc/realloc/free built
 138    on top of it, so that if we use the default sbrk() region we will not
 139    collide with another malloc package trying to do the same thing, if
 140    the application contains any "hidden" calls to malloc/realloc/free (such
 141    as inside a system library).
 142
 143    NOTE:  Defining our own copy of this breaks ANSI conformance. */
 144
 145 PTR
 146 realloc (ptr, size)
 147   PTR ptr;
 148   size_t size;
 149 {
 150   return (mrealloc ((void *) NULL, ptr, size));
 151 }