1 files changed, 60 insertions, 0 deletions
diff --git a/src/arena.c b/src/arena.c
new file mode 100644
index 0000000..aedf0fb
--- /dev/null
+++ b/src/arena.c
@@ -0,0 +1,60 @@
+#include <lcq/pit/arena.h>
+#include <lcq/pit/utils.h>
+
+pit_arena *pit_arena_new(u8 *buf, i64 buf_len, i64 elem_size) {
+    uintptr_t base = (uintptr_t) buf;
+    uintptr_t aligned = pit_align_up(base, sizeof(void *));
+    pit_arena *a = (pit_arena *) aligned;
+    uintptr_t data = aligned + sizeof(pit_arena);
+    i64 offset = (i64) data - (i64) base;
+    i64 remaining = (i64) pit_align_down((uintptr_t) (buf_len - offset), sizeof(void *));
+    if (!a || remaining <= 0) return NULL;
+    a->elem_size = elem_size;
+    a->capacity = remaining;
+    a->next = 0;
+    a->back = remaining;
+    return a;
+}
+void pit_arena_reset(pit_arena *a) {
+    a->next = 0;
+    a->back = a->capacity;
+}
+static i64 pit_arena_byte_idx(pit_arena *a, pit_arena_index idx) {
+    i64 byte_idx = 0; pit_mul(&byte_idx, a->elem_size, idx);
+    return byte_idx;
+}
+pit_arena_index pit_arena_alloc_index(pit_arena *a) {
+    i64 ret = a->next;
+    i64 byte_idx = pit_arena_byte_idx(a, ret);
+    if (byte_idx + a->elem_size >= a->back) { return -1; }
+    a->next += 1;
+    return ret;
+}
+pit_arena_index pit_arena_alloc_array_index(pit_arena *a, i64 num) {
+    i64 ret = a->next;
+    i64 byte_idx = pit_arena_byte_idx(a, ret);
+    i64 byte_len = 0; pit_mul(&byte_len, a->elem_size, num);
+    if (byte_idx + byte_len > a->back) { return -1; }
+    a->next += num;
+    return ret;
+}
+void *pit_arena_alloc(pit_arena *a) {
+    return pit_arena_get(a, pit_arena_alloc_index(a));
+}
+void *pit_arena_alloc_array(pit_arena *a, i64 num) {
+    return pit_arena_get(a, pit_arena_alloc_array_index(a, num));
+}
+
+void *pit_arena_get(pit_arena *a, pit_arena_index idx) {
+    i64 byte_idx = pit_arena_byte_idx(a, idx);
+    if (byte_idx < 0 || byte_idx + a->elem_size >= a->back) { return NULL; }
+    return &a->data[byte_idx];
+}
+
+void *pit_arena_alloc_back(pit_arena *a, i64 sz) {
+    i64 next_byte = pit_arena_byte_idx(a, a->next);
+    i64 back_byte = (i64) pit_align_down((uintptr_t) (a->back - sz), sizeof(void *));
+    if (back_byte < next_byte) return NULL;
+    a->back = back_byte;
+    return &a->data[a->back];
+}