Karatsuba乘法java递归代码不工作？

import java.math.BigInteger;

public class KaratsubaMultiplication {
    public static BigInteger karatsuba(BigInteger x, BigInteger y) {
        int n = Math.max(x.bitLength(), y.bitLength());
        
        // 如果x或y是小整数，直接返回乘积
        if (n <= 2000) {
            return x.multiply(y);
        }
        
        // 将x和y分成两部分
        int half = (n + 32) / 64 * 32;
        BigInteger mask = BigInteger.ONE.shiftLeft(half).subtract(BigInteger.ONE);
        BigInteger xLow = x.and(mask);
        BigInteger xHigh = x.shiftRight(half);
        BigInteger yLow = y.and(mask);
        BigInteger yHigh = y.shiftRight(half);
        
        // 递归计算中间结果
        BigInteger a = karatsuba(xHigh, yHigh);
        BigInteger b = karatsuba(xLow, yLow);
        BigInteger c = karatsuba(xHigh.add(xLow), yHigh.add(yLow)).subtract(a).subtract(b);
        
        // 计算最终结果
        return a.shiftLeft(half * 2).add(c.shiftLeft(half)).add(b);
    }
    
    public static void main(String[] args) {
        BigInteger x = new BigInteger("12345678901234567890");
        BigInteger y = new BigInteger("98765432109876543210");
        BigInteger result = karatsuba(x, y);
        System.out.println(result);
    }
}