Update README

README.md

@@ -8,45 +8,58 @@ cache locality, and reduced memory fragmentation as long as individual items
 don't need to be deallocated. For programs that need to micro-manage individual
 allocations this is not an ideal solution.
 
-Deallocating a region of memory with arenas is extremely fast, because the arena
-length is just set to 0. Allocating memory is also extremely fast.
-This implementation also grows the arena on demand using mmap and mprotect.
+Deallocating a region of memory with arenas is extremely fast, because the
+arena length is just set to 0. Allocating memory is also extremely fast.  This
+implementation also grows the arena on demand using mmap and mprotect.
 Extending the library with a new type of allocation strategy should be easy.
 
 # Reference
 
+
 ## `arena_t arena_new()`
 
 Allocate a new arena.
-The underlying memory is allocated with mmap.
+
+If `arena_new()` fails, the struct member `data` is set to NULL.  This can be
+checked with `arena_new_failed()`
 
 
-## `void arena_delete(arena_t *a)`
+## `bool arena_new_failed(arena_t *a)`
 
-Delete memory mapped for arena.
-Should only be used with arenas from arena\_new().
+Returns true if creating a new arena failed
+
+
+## `int arena_delete(arena_t *a)`
+
+Delete underlying buffer of arena.  Should only be used with arenas from
+`arena_new()`.
+
+Returns 0 on success, -1 on failure
 
 
 ## `arena_t arena_attach(void *ptr, size_t size)`
 
-Attach an arena to an existing memory region.
-The arena will not expand the region if space is exceeded.
+Attach an arena to an existing memory region.  The arena will not expand if
+capacity is exceeded.
 
 
 ## `void *arena_detatch(arena_t arena)`
-Detach an arena from an existing memory region.
+
+Detach an arena from an existing memory region. Returns the underlying data.
 
 
 ## `void arena_reset(arena_t *a)`
-Reset an arena.
+
+Resets an arena.
 
 
 ## `void *arena_alloc(arena_t *a, size_t len)`
-Allocate memory from an arena.
-Returns NULL and sets errno on failure.
+
+Allocate memory with an arena. Returns NULL and sets errno on failure.
 
 
 ## `void *arena_calloc(arena_t *a, size_t nmemb, size_t size)`
-Allocate and zero memory from an arena.
-Returns NULL and sets errno on failure.
+
+Allocate and zero memory with an arena.  Returns NULL and sets errno on
+failure.