Optimize default RNG for the common case

base/runtime/random_generator.odin

@@ -86,6 +86,12 @@ default_random_generator_proc :: proc(data: rawptr, mode: Random_Generator_Mode,
 		   	init(r, 0)
 		}
 
+		switch len(p) {
+		case size_of(u64):
+			// Fast path for a 64-bit destination.
+			(transmute(^u64)raw_data(p))^ = read_u64(r)
+		case:
+			// All other cases.
 			pos := i8(0)
 			val := u64(0)
 			for &v in p {
@@ -97,6 +103,7 @@ default_random_generator_proc :: proc(data: rawptr, mode: Random_Generator_Mode,
 				val >>= 8
 				pos -= 1
 			}
+		}
 
 	case .Reset:
 		seed: u64