1 files changed, 78 insertions, 0 deletions
diff --git a/source/memory/arena.h b/source/memory/arena.h
new file mode 100644
index 0000000..83ff277
--- /dev/null
+++ b/source/memory/arena.h
@@ -0,0 +1,78 @@
+#pragma once
+
+#ifndef ALIGNMENT
+#define ALIGNMENT (2*sizeof(void*))
+#endif
+
+struct Arena {
+  unsigned char* buffer;
+  size_t prev_offset;
+  size_t curr_offset;
+  size_t capacity;
+};
+
+// definition
+b8 is_power_of_two(uintptr_t x);
+uintptr_t fast_modulo(uintptr_t p, uintptr_t a);
+uintptr_t align_forward(uintptr_t ptr, uintptr_t alignment);
+void arena_init(Arena* a, unsigned char *memory, size_t capacity);
+void* arena_alloc(Arena* a, size_t size);
+void arena_clear(Arena* a);
+
+
+// implementation
+b8 is_power_of_two(uintptr_t x) {
+  return (x & (x-1)) == 0;
+}
+
+uintptr_t fast_modulo(uintptr_t p, uintptr_t a) { 
+  return (p & (a - 1)); 
+}
+
+uintptr_t align_forward(uintptr_t ptr, size_t alignment) {
+  uintptr_t p, a, modulo;
+
+  assert(is_power_of_two(alignment));
+
+  p = ptr;
+  a = (uintptr_t)alignment;
+  modulo = fast_modulo(p, a);
+
+  if (modulo != 0) {
+    p += (a - modulo);
+  }
+
+  return p;
+}
+
+void arena_init(Arena* a, unsigned char *memory, size_t capacity) {
+  a->buffer = memory;
+  a->prev_offset = 0;
+  a->curr_offset = 0;
+  a->capacity = capacity;
+}
+
+void* arena_alloc(Arena* a, size_t size) {
+  void *ptr = NULL;
+
+  assert(is_power_of_two(ALIGNMENT));
+
+  uintptr_t curr_ptr = (uintptr_t)a->buffer + a->curr_offset;
+  uintptr_t offset = align_forward(curr_ptr, ALIGNMENT);
+  offset = offset - (uintptr_t)a->buffer;
+  size_t next_offset = offset + size;
+
+  assert(next_offset <= a->capacity);
+
+  ptr = &a->buffer[offset];
+  a->prev_offset = a->curr_offset;
+  a->curr_offset = next_offset;
+  memset(ptr, 0, size);
+
+  return ptr;
+}
+
+void arena_clear(Arena* a) {
+  a->curr_offset = 0;
+  a->prev_offset = 0;
+}