memarray: Add memarray_calloc

The memarray_alloc can be error prone to use as the block returned can
contain data from previous uses. The memarray_calloc call added in this
commit always zeroes the block before returning it to the user.

sys/include/memarray.h

@@ -54,6 +54,8 @@ void memarray_init(memarray_t *mem, void *data, size_t size, size_t num);
  *
  * @pre `mem != NULL`
  *
+ * @note Allocated structure is not cleared before returned
+ *
  * @param[in,out] mem   memarray pool to allocate block in
  *
  * @return pointer to allocated structure, if enough memory was available
@@ -61,6 +63,18 @@ void memarray_init(memarray_t *mem, void *data, size_t size, size_t num);
  */
 void *memarray_alloc(memarray_t *mem);
 
+/**
+ * @brief Allocate and clear memory chunk in memarray pool
+ *
+ * @pre `mem != NULL`
+ *
+ * @param[in,out] mem   memarray pool to allocate block in
+ *
+ * @return pointer to allocated structure, if enough memory was available
+ * @return NULL, on failure
+ */
+void *memarray_calloc(memarray_t *mem);
+
 /**
  * @brief Free memory chunk in memarray pool
  *

sys/memarray/memarray.c

@@ -44,6 +44,15 @@ void *memarray_alloc(memarray_t *mem)
     return free;
 }
 
+void *memarray_calloc(memarray_t *mem)
+{
+    void *new = memarray_alloc(mem);
+    if (new) {
+        memset(new, 0, mem->size);
+    }
+    return new;
+}
+
 void memarray_free(memarray_t *mem, void *ptr)
 {
     assert((mem != NULL) && (ptr != NULL));