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Diff of /xvidcore/src/utils/mem_align.c

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revision 1.1, Fri Mar 8 02:44:58 2002 UTC revision 1.15.2.2, Mon Jun 9 13:55:38 2003 UTC
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1    /*****************************************************************************
2     *
3     *  XVID MPEG-4 VIDEO CODEC
4     *  - Aligned Memory Allocator -
5     *
6     *  Copyright(C) 2002-2003 Edouard Gomez <ed.gomez@free.fr>
7     *
8     *  This program is free software ; you can redistribute it and/or modify
9     *  it under the terms of the GNU General Public License as published by
10     *  the Free Software Foundation ; either version 2 of the License, or
11     *  (at your option) any later version.
12     *
13     *  This program is distributed in the hope that it will be useful,
14     *  but WITHOUT ANY WARRANTY ; without even the implied warranty of
15     *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
16     *  GNU General Public License for more details.
17     *
18     *  You should have received a copy of the GNU General Public License
19     *  along with this program ; if not, write to the Free Software
20     *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
21     *
22     * $Id$
23     *
24     ****************************************************************************/
25    
26    #include <stdlib.h>
27    #include <stdio.h>
28    #include "mem_align.h"
29    
30    /*****************************************************************************
31     * xvid_malloc
32     *
33     * This function allocates 'size' bytes (usable by the user) on the heap and
34     * takes care of the requested 'alignment'.
35     * In order to align the allocated memory block, the xvid_malloc allocates
36     * 'size' bytes + 'alignment' bytes. So try to keep alignment very small
37     * when allocating small pieces of memory.
38     *
39     * NB : a block allocated by xvid_malloc _must_ be freed with xvid_free
40     *      (the libc free will return an error)
41     *
42     * Returned value : - NULL on error
43     *                  - Pointer to the allocated aligned block
44     *
45     ****************************************************************************/
46    
47    void *
48    xvid_malloc(size_t size,
49                            uint8_t alignment)
50    {
51            uint8_t *mem_ptr;
52    
53            if (!alignment) {
54    
55                    /* We have not to satisfy any alignment */
56                    if ((mem_ptr = (uint8_t *) malloc(size + 1)) != NULL) {
57    
58                            /* Store (mem_ptr - "real allocated memory") in *(mem_ptr-1) */
59                            *mem_ptr = 1;
60    
61                            /* Return the mem_ptr pointer */
62                            return (void *)(mem_ptr+1);
63    
64                    }
65    
66            } else {
67                    uint8_t *tmp;
68    
69                    /*
70                     * Allocate the required size memory + alignment so we
71                     * can realign the data if necessary
72                     */
73    
74                    if ((tmp = (uint8_t *) malloc(size + alignment)) != NULL) {
75    
76                            /* Align the tmp pointer */
77                            mem_ptr =
78                                    (uint8_t *) ((ptr_t) (tmp + alignment - 1) &
79                                                             (~(ptr_t) (alignment - 1)));
80    
81                            /*
82                             * Special case where malloc have already satisfied the alignment
83                             * We must add alignment to mem_ptr because we must store
84                             * (mem_ptr - tmp) in *(mem_ptr-1)
85                             * If we do not add alignment to mem_ptr then *(mem_ptr-1) points
86                             * to a forbidden memory space
87                             */
88                            if (mem_ptr == tmp)
89                                    mem_ptr += alignment;
90    
91                            /*
92                             * (mem_ptr - tmp) is stored in *(mem_ptr-1) so we are able to retrieve
93                             * the real malloc block allocated and free it in xvid_free
94                             */
95                            *(mem_ptr - 1) = (uint8_t) (mem_ptr - tmp);
96    
97                            /* Return the aligned pointer */
98                            return (void *) mem_ptr;
99    
100                    }
101            }
102    
103            return NULL;
104    
105    }
106    
107    /*****************************************************************************
108     * xvid_free
109     *
110     * Free a previously 'xvid_malloc' allocated block. Does not free NULL
111     * references.
112     *
113     * Returned value : None.
114     *
115     ****************************************************************************/
116    
117    void
118    xvid_free(void *mem_ptr)
119    {
120    
121            /* *(mem_ptr - 1) give us the offset to the real malloc block */
122            if (mem_ptr)
123                    free((uint8_t *) mem_ptr - *((uint8_t *) mem_ptr - 1));
124    
125    }
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