--- mem_align.c	2002/03/21 00:28:33	1.3
+++ mem_align.c	2002/06/14 13:27:28	1.8
@@ -1,26 +1,117 @@
+/*****************************************************************************
+ *
+ *  XVID MPEG-4 VIDEO CODEC
+ *  - Aligned memory allocator -
+ *
+ *  This program is an implementation of a part of one or more MPEG-4
+ *  Video tools as specified in ISO/IEC 14496-2 standard.  Those intending
+ *  to use this software module in hardware or software products are
+ *  advised that its use may infringe existing patents or copyrights, and
+ *  any such use would be at such party's own risk.  The original
+ *  developer of this software module and his/her company, and subsequent
+ *  editors and their companies, will have no liability for use of this
+ *  software or modifications or derivatives thereof.
+ *
+ *  This program is free software ; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation ; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY ; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program ; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+ *
+ ****************************************************************************/
+/*****************************************************************************
+ *
+ *  History
+ *
+ *  - Thu Jun 13 23:50:07 2002 Added legal header
+ *
+ *  $Id: mem_align.c,v 1.8 2002/06/14 13:27:28 Isibaar Exp $
+ *
+ ****************************************************************************/
+
+
 #include <stdlib.h>
 #include <stdio.h>
 #include "mem_align.h"
 
-void *xvid_malloc(size_t size, uint8_t alignment)
+/*****************************************************************************
+ * xvid_malloc
+ *
+ * This function allocates 'size' bytes (usable by the user) on the heap and
+ * takes care of the requested 'alignment'.
+ * In order to align the allocated memory block, the xvid_malloc allocates
+ * 'size' bytes + 'alignment' bytes. So try to keep alignment very small
+ * when allocating small pieces of memory.
+ *
+ * NB : a block allocated by xvid_malloc _must_ be freed with xvid_free
+ *      (the libc free will return an error)
+ *
+ * Returned value : - NULL on error
+ *                  - Pointer to the allocated aligned block
+ *
+ ****************************************************************************/
+
+void *
+xvid_malloc(size_t size,
+			uint8_t alignment)
 {
 	uint8_t *mem_ptr;
-  
-	if(alignment == 0)
-	{
-		if((mem_ptr = (uint8_t *) malloc(size + 1)) != NULL) {
+
+	if (!alignment) {
+
+		/* We have not to satisfy any alignment */
+		if ((mem_ptr = (uint8_t *) malloc(size + 1)) != NULL) {
+
+			/* Store (mem_ptr - "real allocated memory") in *(mem_ptr-1) */
 			*mem_ptr = 0;
+
+			/* Return the mem_ptr pointer */
 			return (void *) mem_ptr++;
+
 		}
-	}
-	else
-	{
+
+	} else {
 		uint8_t *tmp;
-	
-		if((tmp = (uint8_t *) malloc(size + alignment)) != NULL) {
-			mem_ptr = (uint8_t *)((uint32_t)(tmp + alignment - 1)&(~(uint32_t)(alignment - 1)));
-			*(mem_ptr - 1) = (uint8_t)(mem_ptr - tmp);
+
+		/*
+		 * Allocate the required size memory + alignment so we
+		 * can realign the data if necessary
+		 */
+
+		if ((tmp = (uint8_t *) malloc(size + alignment)) != NULL) {
+
+			/* Align the tmp pointer */
+			mem_ptr =
+				(uint8_t *) ((ptr_t) (tmp + alignment - 1) &
+							 (~(ptr_t) (alignment - 1)));
+
+			/*
+			 * Special case where malloc have already satisfied the alignment
+			 * We must add alignment to mem_ptr because we must store
+			 * (mem_ptr - tmp) in *(mem_ptr-1)
+			 * If we do not add alignment to mem_ptr then *(mem_ptr-1) points
+			 * to a forbidden memory space
+			 */
+			if (mem_ptr == tmp)
+				mem_ptr += alignment;
+
+			/*
+			 * (mem_ptr - tmp) is stored in *(mem_ptr-1) so we are able to retrieve
+			 * the real malloc block allocated and free it in xvid_free
+			 */
+			*(mem_ptr - 1) = (uint8_t) (mem_ptr - tmp);
+
+			/* Return the aligned pointer */
 			return (void *) mem_ptr;
+
 		}
 	}
 
@@ -28,13 +119,22 @@
 
 }
 
-void xvid_free(void *mem_ptr)
-{
-
-	uint8_t *real_ptr;
+/*****************************************************************************
+ * xvid_free
+ *
+ * Free a previously 'xvid_malloc' allocated block. Does not free NULL
+ * references.
+ *
+ * Returned value : None.
+ *
+ ****************************************************************************/
 
-	real_ptr = (uint8_t*)mem_ptr;
+void
+xvid_free(void *mem_ptr)
+{
 
-	free(real_ptr - *(real_ptr -1));
+	/* *(mem_ptr - 1) give us the offset to the real malloc block */
+	if (mem_ptr)
+		free((uint8_t *) mem_ptr - *((uint8_t *) mem_ptr - 1));
 
 }