sarena, add temp allocations

include/ucore/sarena.h

@@ -22,14 +22,20 @@ extern "C" {
  * Once allocated, a piece of memory obtained from the
  * allocator cannot be free'd individually, only the entire SArena can
  * be free'd/reset
-*/
+ */
 typedef struct UCSArena UCSArena;
 struct UCSArena {
-    unsigned char *start; // start of user buffer
-    unsigned char *curr;  // next alloc point
-    unsigned char *end;   // one past end of user buffer
+    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,
@@ -78,12 +78,12 @@ struct UCSArena {
  * is needed.
  * @param var_name Variable name for the allocator
  * @param size_  byte size of the backing array
-*/
+ */
 #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)
+    struct {                              \
+        _Alignas(16) char memory[size_];  \
+    } var_name##_memory;                  \
+    UCSArena var_name = UC_SAR_STATIC_INITIALIZER(var_name##_memory.memory)
 
 /** Allocate space for @type_ , returned memory is aligned to requirements
  * of @type.
@@ -96,16 +96,21 @@ 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)
+// Initialize an UCSArena to allocate from @mem which is @sz bytes
+static inline void uc_sar_init(UCSArena *a, void *mem, size_t sz)
 {
     a->start = a->curr = mem;
     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

@@ -14,17 +14,32 @@ void *uc_sar_alloc(UCSArena *a, size_t sz)
 void *uc_sar_alloc_aligned(UCSArena *a, size_t sz, unsigned int align)
 {
     assert(align != 0);
-    assert((align & (align - 1)) == 0); //power of 2
+    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) {
+    if (start + sz > a->end) {
         return NULL;
-     }
+    }
 
-     a->curr = start + sz;
+    a->curr = start + sz;
 
-     return start;
+    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--;
 }