A 68-year-old man with chronic alcoholism and on warfarin for atrial fibrillation presents to the emergency department with a 3-day history of progressive headache and confusion. His wife reports a minor head trauma from a fall 5 days ago, which he did not initially think was serious. On examination, he is drowsy with a Glasgow Coma Scale of 13/15. Blood pressure is 160/95 mmHg, heart rate 88/min. CT head (non-contrast) shows a crescent-shaped hyperdense collection that crosses the midline and compresses the lateral ventricle. What is the most likely diagnosis?