function S32 os_main();
const SizeU page_size = 4096;

function String
os_read_file(Arena *arena, String name){
  String result = {0};
  FILE *f = fopen((char *)name.str, "rb");
  assert(f);
  fseek(f, 0, SEEK_END);
  result.len = ftell(f);
  fseek(f, 0, SEEK_SET);
  
  result.str = (U8 *)arena_push_size(arena, result.len + 1);
  fread(result.str, result.len, 1, f);
  fclose(f);
  
  result.str[result.len] = 0;
  return result;
}

function SizeU
get_align_offset(SizeU size, SizeU align){
  SizeU mask = align - 1;
  SizeU val = size & mask;
  if(val){
    val = align - val;
  }
  return val;
}

function SizeU
align_up(SizeU size, SizeU align){
  SizeU result = size + get_align_offset(size, align);
  return result;
}

function OS_Memory
os_reserve(SizeU size){
  OS_Memory result = {0};
  SizeU adjusted_size = align_up(size, page_size);
  result.data = VirtualAlloc(0, adjusted_size, MEM_RESERVE, PAGE_READWRITE);
  assert_msg(result.data, "Failed to reserve virtual memory");
  result.reserve = adjusted_size;
  return result;
}

function void
os_commit(OS_Memory *m, SizeU size){
  SizeU commit = align_up(size, page_size);
  void *p = VirtualAlloc((U8 *)m->data + m->commit, commit, MEM_COMMIT, PAGE_READWRITE);
  assert_msg(p, "Failed to commit more memory");
  m->commit += commit;
}