[cvs] / xvidcore / src / utils / mem_align.c Repository:
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revision 1.3, Thu Mar 21 00:28:33 2002 UTC revision 1.15.2.2, Mon Jun 9 13:55:38 2003 UTC
# Line 1  Line 1 
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>  #include <stdlib.h>
27  #include <stdio.h>  #include <stdio.h>
28  #include "mem_align.h"  #include "mem_align.h"
29    
30  void *xvid_malloc(size_t size, uint8_t alignment)  /*****************************************************************************
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;          uint8_t *mem_ptr;
52    
53          if(alignment == 0)          if (!alignment) {
54          {  
55                    /* We have not to satisfy any alignment */
56                  if((mem_ptr = (uint8_t *) malloc(size + 1)) != NULL) {                  if((mem_ptr = (uint8_t *) malloc(size + 1)) != NULL) {
57                          *mem_ptr = 0;  
58                          return (void *) mem_ptr++;                          /* 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          else  
66          {          } else {
67                  uint8_t *tmp;                  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) {                  if((tmp = (uint8_t *) malloc(size + alignment)) != NULL) {
75                          mem_ptr = (uint8_t *)((uint32_t)(tmp + alignment - 1)&(~(uint32_t)(alignment - 1)));  
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);                          *(mem_ptr - 1) = (uint8_t)(mem_ptr - tmp);
96    
97                            /* Return the aligned pointer */
98                          return (void *) mem_ptr;                          return (void *) mem_ptr;
99    
100                  }                  }
101          }          }
102    
# Line 28  Line 104 
104    
105  }  }
106    
107  void xvid_free(void *mem_ptr)  /*****************************************************************************
108  {   * xvid_free
109     *
110          uint8_t *real_ptr;   * Free a previously 'xvid_malloc' allocated block. Does not free NULL
111     * references.
112     *
113     * Returned value : None.
114     *
115     ****************************************************************************/
116    
117          real_ptr = (uint8_t*)mem_ptr;  void
118    xvid_free(void *mem_ptr)
119    {
120    
121          free(real_ptr - *(real_ptr -1));          /* *(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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