1 files changed, 108 insertions, 0 deletions
diff --git a/arena.h b/arena.h
new file mode 100644
index 0000000..c99fc97
--- /dev/null
+++ b/arena.h
@@ -0,0 +1,108 @@
+#ifndef ARENA_H_
+#define ARENA_H_
+
+#include <stdlib.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <assert.h>
+
+typedef struct region region;
+
+struct region {
+  region *next;
+  size_t cap;
+  size_t len;
+  uintptr_t data[];
+};
+
+typedef struct {
+  region *beg;
+  region *end;
+} arena;
+
+void *arena_alloc(arena *a, size_t size);
+void arena_free(arena *a);
+void grow_da(void *slice, size_t size, arena *arena);
+
+
+#define new(a, t, c) (t *)arena_alloc(a, sizeof(t)*c)
+
+#define ARENA_REGION_DEFAULT_CAPACITY (8*1024);
+
+// from nullprogram
+#define push(slice, arena) \
+  ((slice)->len >= (slice)->cap \
+	? grow(slice, sizeof(*(slice)->data), arena), \
+	  (slice)->data + (slice)->len++ \
+	: (slice)->data + (slice)->len++)
+
+#endif //ARENA_H_
+
+#ifdef ARENA_IMPLEMENTATION
+
+region *new_region(size_t cap) {
+  size_t size_bytes = sizeof(region) + sizeof(uintptr_t)*cap;
+  region *r = (region *)malloc(size_bytes);
+  assert(r);
+  r->next = NULL;
+  r->len = 0;
+  r->cap = cap;
+  return r;
+}
+
+void *arena_alloc(arena *a, size_t size_bytes) {
+  size_t size = (size_bytes + sizeof(uintptr_t)-1)/sizeof(uintptr_t);
+  
+  if (a->end == NULL) {
+	assert(a->beg == NULL);
+	size_t capacity = ARENA_REGION_DEFAULT_CAPACITY;
+	if (capacity < size) capacity = size;
+	a->beg = new_region(capacity);
+	a->end = a->beg;
+  }
+
+  while (a->end->len + size < a->end->cap && a->end->next != NULL) {
+	a->end = a->end->next;
+  }
+  
+  if (a->end->len + size > a->end->cap) {
+	size_t capacity = ARENA_REGION_DEFAULT_CAPACITY;
+	if (capacity < size) capacity = size;
+	a->beg = new_region(capacity);
+	a->end->next = new_region(capacity);
+	a->end = a->end->next;
+  }
+
+  void *p = &a->end->data[a->end->len];
+  a->end->len += size;
+  return memset(p, 0, size);
+}
+
+void arena_free(arena *a) {
+  region *r = a->beg;
+  while (r != NULL) {
+	region *r0 = r;
+	r = r0->next;
+	free(r0);
+  }
+}
+
+void grow(void *slice, size_t size, arena *arena) {
+  struct {
+	void *data;
+	size_t len;
+	size_t cap;
+  } replica;
+  memcpy(&replica, slice, sizeof(replica));
+
+  replica.cap = replica.cap ? replica.cap : 1;
+  void *data = arena_alloc(arena, size*2*replica.cap);
+  replica.cap *= 2;
+  if (replica.len) {
+	memcpy(data, replica.data, size*replica.len);
+  }
+  replica.data = data;
+
+  memcpy(slice, &replica, sizeof(replica));
+}
+#endif // ARENA_IMPLEMENTATION