static int F1(int op, int a, int b, int c) {
		if (c < 0) c ^= 0xFFFF0000;
		if ((a & ~0x1F | b & ~0x1F | c & ~0xFFFF) != 0) {
			System.out.println("Illegal Operand(s) for F1 Format.");
			bug(1);
		}
		return op << 26 | a << 21 | b << 16 | c;
	}