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
realloc(ptr,size)40 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 free (ptr);
51 return malloc (0);
52 }
53 else if (ptr == NULL)
54 return 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 = malloc (size);
69 if (result != NULL)
70 {
71 memcpy (result, ptr, size);
72 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 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 free (ptr);
104 _heaplimit = oldlimit;
105 result = 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) malloc (blocks * BLOCKSIZE);
113 else
114 {
115 __ptr_t previous = malloc ((block - _heapindex) * BLOCKSIZE);
116 (void) malloc (blocks * BLOCKSIZE);
117 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 = malloc (size);
137 if (result == NULL)
138 return NULL;
139 memcpy (result, ptr, min (size, (size_t) 1 << type));
140 free (ptr);
141 }
142 break;
143 }
144
145 return result;
146 }
147