Organization cleanup, stage arena to Scratch_Arena

base_arena.cpp

@@ -114,3 +114,100 @@ static CRT_Heap make_crt_heap() {
   result.deallocate = crt_deallocate;
   return result;
 }
+
+//-----------------------------------------------------------------------------
+// Memory OS
+//-----------------------------------------------------------------------------
+struct OS_Memory{
+  size_t commit, reserve;
+  U8 *data;
+};
+CORE_Static OS_Memory os_reserve(size_t size);
+CORE_Static B32 os_commit(OS_Memory *m, size_t size);
+CORE_Static void os_release(OS_Memory *m);
+CORE_Static B32 os_decommit_pos(OS_Memory *m, size_t pos);
+
+//-----------------------------------------------------------------------------
+// Memory arenas
+//-----------------------------------------------------------------------------
+global const size_t default_reserve_size   = gib(4);
+global const size_t default_alignment      = 8;
+global const size_t additional_commit_size = mib(1);
+struct Arena : Allocator {
+  OS_Memory memory;
+  size_t alignment;
+  size_t len;
+  String debug_string;
+};
+
+CORE_Static void
+  arena_pop_pos(Arena *arena, size_t pos){
+  pos = clamp_top(pos, arena->len);
+  arena->len = pos;
+}
+
+CORE_Static void *
+  arena_pop(Arena *arena, size_t size){
+  size = clamp_top(size, arena->len);
+  arena->len -= size;
+  return arena->memory.data + arena->len;
+}
+
+CORE_Static void
+  arena_release(Arena *arena){
+  os_release(&arena->memory);
+}
+
+CORE_Static void
+  arena_clear(Arena *arena){
+  arena_pop_pos(arena, 0);
+}
+
+CORE_Static void *
+  arena_push_size(Arena *a, size_t size){
+  size_t generous_size = size + a->alignment;
+  if(a->len+generous_size>a->memory.commit){
+    assert(a->memory.reserve > 0);
+    B32 result = os_commit(&a->memory, generous_size+additional_commit_size);
+    assert(result);
+  }
+
+  a->len = align_up(a->len, a->alignment);
+  assert(a->memory.reserve > a->len + size);
+  void *result = (U8*)a->memory.data + a->len;
+  a->len += size;
+
+  return result;
+}
+
+CORE_Static Arena
+  push_arena(Allocator *allocator, size_t size, String debug_name) {
+  Arena result = {};
+  result.memory.data = (U8 *)allocate_size(allocator, size);
+  result.memory.reserve = size;
+  result.alignment = default_alignment;
+  result.debug_string = debug_name;
+  result.allocate     = (Allocator::Allocate *)arena_push_size;
+  result.deallocate   = (Allocator::Deallocate *)deallocate_stub;
+  return result;
+}
+
+CORE_Static void
+  arena_init(Arena *a, String debug_name){
+  a->memory       = os_reserve(default_reserve_size);
+  a->alignment    = default_alignment;
+  a->debug_string = debug_name;
+  a->allocate     = (Allocator::Allocate *)arena_push_size;
+  a->deallocate   = (Allocator::Deallocate *)deallocate_stub;
+}
+
+CORE_Static Arena
+  arena_sub(Arena *base, size_t size, String debug_name) {
+  Arena result = {};
+  result.memory.data = (U8 *)arena_push_size(base, size);
+  result.memory.commit = size;
+  result.memory.reserve = size;
+  result.alignment = default_alignment;
+  result.len = 0;
+  return result;
+}