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Member "threads/malloc/realloc.c" (16 Mar 1994, 4460 Bytes) of package /linux/misc/old/pthreads-3.14.tar.gz:


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    1 /* Change the size of a block allocated by `malloc'.
    2    Copyright 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
    3              Written May 1989 by Mike Haertel.
    4 
    5 This 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 This 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 this 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 #ifndef _MALLOC_INTERNAL
   24 #define _MALLOC_INTERNAL
   25 #include <malloc.h>
   26 #endif
   27 
   28 #define min(A, B) ((A) < (B) ? (A) : (B))
   29 
   30 /* Debugging hook for realloc.  */
   31 __ptr_t (*__realloc_hook) __P ((__ptr_t __ptr, size_t __size));
   32 
   33 /* Resize the given region to the new size, returning a pointer
   34    to the (possibly moved) region.  This is optimized for speed;
   35    some benchmarks seem to indicate that greater compactness is
   36    achieved by unconditionally allocating and copying to a
   37    new region.  This module has incestuous knowledge of the
   38    internals of both free and malloc. */
   39 __ptr_t
   40 pthread_realloc (ptr, size)
   41      __ptr_t ptr;
   42      size_t size;
   43 {
   44   __ptr_t result;
   45   int type;
   46   size_t block, blocks, oldlimit;
   47 
   48   if (size == 0)
   49     {
   50       pthread_free (ptr);
   51       return pthread_malloc (0);
   52     }
   53   else if (ptr == NULL)
   54     return pthread_malloc (size);
   55 
   56   if (__realloc_hook != NULL)
   57     return (*__realloc_hook) (ptr, size);
   58 
   59   block = BLOCK (ptr);
   60 
   61   type = _heapinfo[block].busy.type;
   62   switch (type)
   63     {
   64     case 0:
   65       /* Maybe reallocate a large block to a small fragment.  */
   66       if (size <= BLOCKSIZE / 2)
   67     {
   68       result = pthread_malloc (size);
   69       if (result != NULL)
   70         {
   71           memcpy (result, ptr, size);
   72           pthread_free (ptr);
   73           return result;
   74         }
   75     }
   76 
   77       /* The new size is a large allocation as well;
   78      see if we can hold it in place. */
   79       blocks = BLOCKIFY (size);
   80       if (blocks < _heapinfo[block].busy.info.size)
   81     {
   82       /* The new size is smaller; return
   83          excess memory to the free list. */
   84       _heapinfo[block + blocks].busy.type = 0;
   85       _heapinfo[block + blocks].busy.info.size
   86         = _heapinfo[block].busy.info.size - blocks;
   87       _heapinfo[block].busy.info.size = blocks;
   88       pthread_free (ADDRESS (block + blocks));
   89       result = ptr;
   90     }
   91       else if (blocks == _heapinfo[block].busy.info.size)
   92     /* No size change necessary.  */
   93     result = ptr;
   94       else
   95     {
   96       /* Won't fit, so allocate a new region that will.
   97          Free the old region first in case there is sufficient
   98          adjacent free space to grow without moving. */
   99       blocks = _heapinfo[block].busy.info.size;
  100       /* Prevent free from actually returning memory to the system.  */
  101       oldlimit = _heaplimit;
  102       _heaplimit = 0;
  103       pthread_free (ptr);
  104       _heaplimit = oldlimit;
  105       result = pthread_malloc (size);
  106       if (result == NULL)
  107         {
  108           /* Now we're really in trouble.  We have to unfree
  109          the thing we just freed.  Unfortunately it might
  110          have been coalesced with its neighbors.  */
  111           if (_heapindex == block)
  112             (void) pthread_malloc (blocks * BLOCKSIZE);
  113           else
  114         {
  115           __ptr_t previous = pthread_malloc ((block - _heapindex) * BLOCKSIZE);
  116           (void) pthread_malloc (blocks * BLOCKSIZE);
  117           pthread_free (previous);
  118         }
  119           return NULL;
  120         }
  121       if (ptr != result)
  122         memmove (result, ptr, blocks * BLOCKSIZE);
  123     }
  124       break;
  125 
  126     default:
  127       /* Old size is a fragment; type is logarithm
  128      to base two of the fragment size.  */
  129       if (size > (size_t) (1 << (type - 1)) && size <= (size_t) (1 << type))
  130     /* The new size is the same kind of fragment.  */
  131     result = ptr;
  132       else
  133     {
  134       /* The new size is different; allocate a new space,
  135          and copy the lesser of the new size and the old. */
  136       result = pthread_malloc (size);
  137       if (result == NULL)
  138         return NULL;
  139       memcpy (result, ptr, min (size, (size_t) 1 << type));
  140       pthread_free (ptr);
  141     }
  142       break;
  143     }
  144 
  145   return result;
  146 }