package generated.javacard.copycardMoneySecure.copycard;

import javacard.framework.ISOException;
import javacard.framework.ISO7816;

public class Math {

	public static short plus(short x, short y) {
		short res = (short) (x + y);
		if (x < 0 && y < 0 && res >= 0)
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		if (x > 0 && y > 0 && res < 0)
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		return res;
	}

	public static short minus(short x, short y) {
		short res = (short) (x - y);
		if (0 <= x && y < 0 && res < 0) // 0 <= x is important!
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		if (x < 0 && 0 < y && res > 0)
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		return res;
	}

	public static short div(short x, short y) {
		if (y == 0)
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		if (y == -1 && x == -32768)
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		return (short) (x / y);
	}

	public static short mod(short x, short y) {
		if (y == 0)
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		return (short) (x % y);
	}

	public static short mult(short x, short y) {
		if (x == 0 || y == 0)
			return 0;
		if (x == 1)
			return y;
		if (y == 1)
			return x;
		if (x == -32768 || y == -32768)
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		byte sgn = (x < 0 ? (y < 0 ? 1 : (byte) -1) : (y < 0 ? (byte) -1 : 1));
		if (x < 0)
			x = (short) -x;
		if (y < 0)
			y = (short) -y;
		// check for overflows
		short xh = (short) (x >> 8);
		short yh = (short) (y >> 8);
		if (xh != 0 && yh != 0)
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		short xl = (short) (x & 0xFF);
		short yl = (short) (y & 0xFF);
		short r1 = (short) (xl * yl);
		short r2 = (short) (xl * yh);
		short r3 = (short) (xh * yl);
		// x * y = 256 * (xh * yl + yh * xl) + xl * yl
		//   r4H r4L   0   0 
		// +   0 r3H r3L   0 
		// +   0 r2H r2L   0 
		// +   0   0 r1H r1L
		short r = (short) (r2 + r3);
		short res = (short) (r * 256 + r1);
		if (sgn < 0 && r == 128 && r1 == 0)
			return -32768;
		if (r > 127 || res < 0)
			ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
		return (short) (sgn * res);
	}
}