diff --git a/include/ucore/sarena.h b/include/ucore/sarena.h
index 29f7188..4303eee 100644
--- a/include/ucore/sarena.h
+++ b/include/ucore/sarena.h
@@ -3,6 +3,7 @@
 
 #include <stddef.h>
 #include <stdint.h>
+#include <assert.h>
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -82,8 +83,8 @@ struct UCSTmpAlloc {
 #define UC_SAR_ALLOC_DEF(var_name, size_) \
     struct {                              \
         _Alignas(16) char memory[size_];  \
-    } var_name##_memory;                  \
-    UCSArena var_name = UC_SAR_STATIC_INITIALIZER(var_name##_memory.memory)
+    } var_name##_arena_memory;            \
+    UCSArena var_name = UC_SAR_STATIC_INITIALIZER(var_name##_arena_memory.memory)
 
 /** Allocate space for @type_ , returned memory is aligned to requirements
  * of @type.
@@ -99,29 +100,83 @@ struct UCSTmpAlloc {
 #define UC_SAR_ALLOC_ALIGNED(allocator, type_) uc_sar_alloc_aligned((allocator), sizeof(type_), _Alignof(type_))
 
 // Initialize an UCSArena to allocate from @mem which is @sz bytes
-static inline void uc_sar_init(UCSArena *a, void *mem, size_t sz)
+static inline void uc_sar_init(UCSArena *arena, void *memory, size_t sz)
 {
-    a->start = a->curr = mem;
-    a->end = a->start + sz;
+    arena->start = arena->curr = (unsigned char *)memory;
+    arena->end = arena->start + sz;
 }
 
 // begin temporary allocation. All allocations afterwards will be released in uc_sar_tmp_end
-UCSTmpAlloc uc_sar_tmp_begin(UCSArena *a);
+static inline UCSTmpAlloc uc_sar_tmp_begin(UCSArena *arena)
+{
+    UCSTmpAlloc state = {.alloc_point = arena->curr, .arena = arena};
+    arena->tmp_allocs++;
+    return state;
+}
 
 // end temporary allocations, releaseing all allocations since the most recent uc_sar_tmp_begin
-void uc_sar_tmp_end(const UCSTmpAlloc *state);
+static inline void uc_sar_tmp_end(const UCSTmpAlloc *state)
+{
+    UCSArena *arena = state->arena;
+    assert(arena->tmp_allocs > 0);
+    arena->curr = state->alloc_point;
+    arena->tmp_allocs--;
+}
 
 // Allocate @sz bytes from the UCSArena. Returns NULL if not enough space
-void *uc_sar_alloc(UCSArena *a, size_t sz);
+void *uc_sar_alloc(UCSArena *arena, size_t sz)
+{
+    if (arena->curr + sz > arena->end) {
+        return NULL;
+    }
+    void *start = arena->curr;
+    arena->curr += sz;
+    return start;
+}
 
 // Allocate @sz bytes from the UCSArena, returned pointer is aligned to @align
 // Returns NULL if not enough space
-void *uc_sar_alloc_aligned(UCSArena *a, size_t sz, unsigned int align) [[gnu::alloc_align(2)]];
-
-static inline void uc_sar_reset(UCSArena *a)
+void *uc_sar_alloc_aligned(UCSArena *arena, size_t sz, unsigned int align) [[gnu::alloc_align(3)]]
 {
-    a->curr = a->start;
+    assert(align != 0);
+    assert((align & (align - 1)) == 0);  // power of 2
+
+    uintptr_t curr = (uintptr_t)arena->curr;
+    uintptr_t aligned = (curr + (align - (uintptr_t)1)) & ~(align - (uintptr_t)1);
+    unsigned char *start = (unsigned char *)aligned;
+
+    if (start + sz > arena->end) {
+        return NULL;
+    }
+
+    arena->curr = start + sz;
+
+    return start;
 }
+
+static inline void uc_sar_reset(UCSArena *arena)
+{
+    arena->curr = arena->start;
+}
+
+// Arena size in bytes
+static inline size_t uc_sar_size(const UCSArena *arena)
+{
+    return (size_t)(arena->end - arena->start);
+}
+
+// Used bytes of the arena
+static inline size_t uc_sar_used(const UCSArena *arena)
+{
+    return (size_t)(arena->curr - arena->start);
+}
+
+// Available unused bytes in the arena
+static inline size_t uc_sar_available(const UCSArena *arena)
+{
+    return uc_sar_size(arena) - uc_sar_used(arena);
+}
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/sarena.c b/src/sarena.c
deleted file mode 100644
index 77782a0..0000000
--- a/src/sarena.c
+++ /dev/null
@@ -1,45 +0,0 @@
-#include <assert.h>
-#include "ucore/sarena.h"
-
-void *uc_sar_alloc(UCSArena *a, size_t sz)
-{
-    if (a->curr + sz > a->end) {
-        return NULL;
-    }
-    void *start = a->curr;
-    a->curr += sz;
-    return start;
-}
-
-void *uc_sar_alloc_aligned(UCSArena *a, size_t sz, unsigned int align)
-{
-    assert(align != 0);
-    assert((align & (align - 1)) == 0);  // power of 2
-
-    uintptr_t curr = (uintptr_t)a->curr;
-    uintptr_t aligned = (curr + (align - (uintptr_t)1)) & ~(align - (uintptr_t)1);
-    unsigned char *start = (unsigned char *)aligned;
-
-    if (start + sz > a->end) {
-        return NULL;
-    }
-
-    a->curr = start + sz;
-
-    return start;
-}
-
-UCSTmpAlloc uc_sar_tmp_begin(UCSArena *a)
-{
-    UCSTmpAlloc state = {.alloc_point = a->curr, .arena = a};
-    a->tmp_allocs++;
-    return state;
-}
-
-void uc_sar_tmp_end(const UCSTmpAlloc *state)
-{
-    UCSArena *a = state->arena;
-    assert(a->tmp_allocs > 0);
-    a->curr = state->alloc_point;
-    a->tmp_allocs--;
-}