Add av_calloc() helper.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit ccecab4a0d)

libavutil/mem.c

@@ -168,6 +168,13 @@ void *av_mallocz(size_t size)
     return ptr;
 }
 
+void *av_calloc(size_t nmemb, size_t size)
+{
+    if (size <= 0 || nmemb >= INT_MAX / size)
+        return NULL;
+    return av_mallocz(nmemb * size);
+}
+
 char *av_strdup(const char *s)
 {
     char *ptr= NULL;

libavutil/mem.h

@@ -106,6 +106,18 @@ void av_free(void *ptr);
  */
 void *av_mallocz(size_t size) av_malloc_attrib av_alloc_size(1);
 
+/**
+ * Allocate a block of nmemb * size bytes with alignment suitable for all
+ * memory accesses (including vectors if available on the CPU) and
+ * zero all the bytes of the block.
+ * The allocation will fail if nmemb * size is greater than or equal
+ * to INT_MAX.
+ * @param nmemb
+ * @param size
+ * @return Pointer to the allocated block, NULL if it cannot be allocated.
+ */
+void *av_calloc(size_t nmemb, size_t size) av_malloc_attrib;
+
 /**
  * Duplicate the string s.
  * @param s string to be duplicated