Add arena allocator

src/arena.c

@@ -0,0 +1,101 @@
+#include <assert.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <string.h>
+
+struct ucl_arena {
+    size_t object_size;
+    size_t capacity;
+    void *objects;
+    int *used_map;
+};
+
+#define DIV_ROUND_UP(numerator, denominator) \
+    (((numerator) + (denominator) - 1) / (denominator))
+
+#define INT_BITS (CHAR_BIT * sizeof(int))
+
+struct ucl_arena *ucl_arena_create(size_t object_size, size_t capacity) {
+    struct ucl_arena *arena = malloc(sizeof(*arena));
+    size_t used_map_size = DIV_ROUND_UP(capacity, INT_BITS) * sizeof(int);
+
+    arena->object_size = object_size;
+    arena->capacity = capacity;
+    arena->objects = malloc(capacity * object_size);
+    arena->used_map = malloc(used_map_size);
+
+    memset(arena->used_map, 0, used_map_size);
+
+    assert(arena->objects != NULL);
+    assert(arena->used_map != NULL);
+
+    return arena;
+}
+
+void ucl_arena_map(struct ucl_arena *arena, void (*map_function)(struct ucl_arena * arena, void *object)) {
+    size_t used_map_ints = DIV_ROUND_UP(arena->capacity, INT_BITS);
+
+    for (int i = 0; i < used_map_ints; i++ ) {
+        // TODO: Allow for 'put' in map
+        int map = arena->used_map[i];
+        while (map) {
+            int bit_index = __builtin_ffs(map) - 1;
+            int index = bit_index + INT_BITS * i;
+            void *obj = arena->objects + (index * arena->object_size);
+            map_function(arena, obj);
+            map &= ~(1 << bit_index);
+        }
+    }
+}
+
+int total_arena_gets = 0;
+
+void *ucl_arena_get(struct ucl_arena *arena) {
+    int used_map_ints = DIV_ROUND_UP(arena->capacity, INT_BITS);
+    for (int i = 0; i < used_map_ints; i++ ) {
+        // TODO: Maybe keep a cache of available used_map_ints
+        int map = arena->used_map[i];
+        if (!(~map)) {
+            continue;
+        }
+
+        int bit_index = __builtin_ffs(~map) - 1;
+        int index = bit_index + INT_BITS * i;
+        if (index >= arena->capacity) {
+            // This might happen in the last used_map_int when (capacity % int_bits != 0)
+            return NULL;
+        }
+        arena->used_map[i] |= 1 << bit_index;
+        total_arena_gets++;
+        return arena->objects + (index * arena->object_size);
+    }
+
+    return NULL;
+}
+
+int total_arena_puts = 0;
+
+void ucl_arena_put(struct ucl_arena *arena, void *object) {
+
+    if (object == NULL) {
+        return;
+    }
+
+    ptrdiff_t offset = object - arena->objects;
+    unsigned int index = offset / arena->object_size;
+    unsigned int int_index = index / INT_BITS;
+    unsigned int bit_index = index % INT_BITS;
+
+    assert(offset % arena->object_size == 0);
+    assert(index >= 0);
+    assert(index < arena->capacity);
+
+    assert(arena->used_map[int_index] & (1 << bit_index));
+    //if (arena->used_map[int_index] & (1 << bit_index)) {
+        total_arena_puts++;
+    //}
+
+
+    arena->used_map[int_index] &= ~(1 << bit_index);
+}