avcodec: Add av_fast_padded_malloc().

Wrapper around av_fast_malloc() that keeps FF_INPUT_BUFFER_PADDING_SIZE
zero-padded bytes at the end of the used buffer.

Based on a patch by Reimar Döffinger <Reimar.Doeffinger@gmx.de>.

doc/APIchanges

@@ -13,6 +13,11 @@ libavutil:   2011-04-18
 
 API changes, most recent first:
 
+2012-02-01 - xxxxxxx - lavc 54.01.0
+  Add av_fast_padded_malloc() as alternative for av_realloc() when aligned
+  memory is required. The buffer will always have FF_INPUT_BUFFER_PADDING_SIZE
+  zero-padded bytes at the end.
+
 2012-01-31 - xxxxxxx - lavf 54.01.0
   Add avformat_get_riff_video_tags() and avformat_get_riff_audio_tags().
 

libavcodec/avcodec.h

@@ -4070,6 +4070,15 @@ void *av_fast_realloc(void *ptr, unsigned int *size, size_t min_size);
  */
 void av_fast_malloc(void *ptr, unsigned int *size, size_t min_size);
 
+/**
+ * Allocate a buffer with padding, reusing the given one if large enough.
+ *
+ * Same behaviour av_fast_malloc but the buffer has additional
+ * FF_INPUT_PADDING_SIZE at the end which will always memset to 0.
+ *
+ */
+void av_fast_padded_malloc(void *ptr, unsigned int *size, size_t min_size);
+
 /**
  * Copy image src to dst. Wraps av_picture_data_copy() above.
  */

libavcodec/utils.c

@@ -80,6 +80,19 @@ void av_fast_malloc(void *ptr, unsigned int *size, size_t min_size)
     *size= min_size;
 }
 
+void av_fast_padded_malloc(void *ptr, unsigned int *size, size_t min_size)
+{
+    void **p = ptr;
+    if (min_size > SIZE_MAX - FF_INPUT_BUFFER_PADDING_SIZE) {
+        av_freep(p);
+        *size = 0;
+        return;
+    }
+    av_fast_malloc(p, size, min_size + FF_INPUT_BUFFER_PADDING_SIZE);
+    if (*size)
+        memset((uint8_t *)*p + min_size, 0, FF_INPUT_BUFFER_PADDING_SIZE);
+}
+
 /* encoder management */
 static AVCodec *first_avcodec = NULL;