Merge pull request #457 from FrankBoesing/patch-4

usb.c / interrupt - callbacks use ctz()

teensy4/usb.c

 				endpoint0_complete();
 			}
 			completestatus &= endpointN_notify_mask;
+#if 1
+			if (completestatus) {
+
+				// transmit:
+				uint32_t tx = completestatus >> 16;
+				while (tx) {
+					int p=__builtin_ctz(tx);
+					run_callbacks(endpoint_queue_head + p * 2 + 1);
+					tx &= ~(1<<p);
+				}
+
+				// receive:
+				uint32_t rx = completestatus & 0xffff;
+				while(rx) {
+					int p=__builtin_ctz(rx);
+					run_callbacks(endpoint_queue_head + p * 2);
+					rx &= ~(1<<p);
+				};
+			}
+#else
 			if (completestatus) {
 				int i;   // TODO: optimize with __builtin_ctz()
 				for (i=2; i <= NUM_ENDPOINTS; i++) {
 					}
 				}
 			}
+#endif
+
 		}
 	}
 	if (status & USB_USBSTS_URI) { // page 3164