sarena, add temp allocations

include/ucore/sarena.h

@@ -28,8 +28,14 @@ struct UCSArena {
     unsigned char *start;  // start of user buffer
     unsigned char *curr;   // next alloc point
     unsigned char *end;    // one past end of user buffer
+    int tmp_allocs;        // no of uc_sar_tmp_begin calls
 };
 
+typedef struct UCSTmpAlloc UCSTmpAlloc;
+struct UCSTmpAlloc {
+    unsigned char *alloc_point;
+    UCSArena *arena;
+};
 /** Initialize a UCSArena with predefined backing array.
  *
  * @data must be an array type
@@ -39,8 +45,7 @@ struct UCSArena {
  * UCSArena a = UC_BV_STATIC_INITIALIZER(v);
  * @endcode
  */
-#define UC_SAR_STATIC_INITIALIZER(data)\
-    UC_SAR_INITIALIZER((data), sizeof(data))
+#define UC_SAR_STATIC_INITIALIZER(data) UC_SAR_INITIALIZER((data), sizeof(data))
 
 /** Initializer for UCSArena with predefined memory
  * Use as
@@ -54,12 +59,7 @@ struct UCSArena {
  * UCSArena a = UC_BV_INIT(m, 128);
  * @endcode
  */
-#define UC_SAR_INITIALIZER(data, sz)\
-    {\
-    (data),\
-    (data),\
-    (data) + sz\
-    }
+#define UC_SAR_INITIALIZER(data, sz) {(data), (data), (data) + sz}
 
 /** Initialize a UCSArena with an array as the backing memory to allocate from.
  * The macro can be used at local scope to allocate memory automatic on the stack,
@@ -96,8 +96,7 @@ struct UCSArena {
  * struct Foo *str = UC_SAR_ALLOC_ALIGNED(&my_allocator, struct Foo[32]);
  * @endcode
  */
-#define UC_SAR_ALLOC_ALIGNED(allocator, type_) \
-    uc_sar_alloc_aligned((allocator), sizeof (type_), _Alignof(type_))
+#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)
@@ -106,6 +105,12 @@ static  inline void uc_sar_init(UCSArena *a, void *mem, size_t sz)
     a->end = a->start + sz;
 }
 
+// begin temporary allocation. All allocations afterwards will be released in uc_sar_tmp_end
+UCSTmpAlloc uc_sar_tmp_begin(UCSArena *a);
+
+// end temporary allocations, releaseing all allocations since the most recent uc_sar_tmp_begin
+void uc_sar_tmp_end(const UCSTmpAlloc *state);
+
 // Allocate @sz bytes from the UCSArena. Returns NULL if not enough space
 void *uc_sar_alloc(UCSArena *a, size_t sz);
 
@@ -113,7 +118,6 @@ void *uc_sar_alloc(UCSArena *a, size_t sz);
 // 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)
 {
     a->curr = a->start;

src/sarena.c

@@ -28,3 +28,18 @@ void *uc_sar_alloc_aligned(UCSArena *a, size_t sz, unsigned int align)
 
     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--;
+}