超大数相加，相乘

超出long上限的大数相加，相乘算法。

public class StringCompute {

	private static final class instanceClass {
		public static final StringCompute instance = new StringCompute();
	}

	private static StringCompute getInstance() {
		return instanceClass.instance;
	}

	private StringCompute() {
	}

	/**
	 * [方法功能说明]
	 * 
	 * @param args
	 */
	public static void main(String[] args) {
				
		long start = System.currentTimeMillis();
		
		StringCompute.getInstance().multiply("4545687745456468777878787878787", "46465464646465445456656465");
		
		System.out.println((System.currentTimeMillis() - start)+"[ms]");
		
		start = System.currentTimeMillis();
			
		System.out.println(StringCompute.getInstance().add("4545687745456468777878787878787", "46465464646465445456656465"));
			
		System.out.println((System.currentTimeMillis() - start)+"[ms]");
	}


	/**
	 * 
	 * [超大数相加]
	 * 
	 * @param a
	 * @param b
	 * @return
	 */
	private String add(String a, String b) {
		StringBuilder c = new StringBuilder("");
		char[] aArray = a.toCharArray();
		char[] bArray = b.toCharArray();
		int upper = 0; // 进位
		int length = aArray.length < bArray.length ? aArray.length
				: bArray.length;
		char[] maxArray = aArray.length > bArray.length ? aArray : bArray;
		int i = 0;
		for (; i < length; i++) {
			int temp = Integer.parseInt("" + (aArray[aArray.length - i - 1]))
					+ Integer.parseInt("" + bArray[bArray.length - i - 1])
					+ upper;

			upper = temp / 10;
			c.append(temp % 10);

		}
		if (aArray.length != bArray.length) {
			// c.append(maxArray[maxArray.length - i -1]+upper);
			for (int j = (maxArray.length - i - 1); j >= 0; j--) {
				int temp = Integer.parseInt("" + (maxArray[j])) + upper;
				upper = temp / 10;
				c.append(temp % 10);
			}
		}
		if (upper != 0) {
			c.append(upper);
		}
		return c.reverse().toString();
	}

	private void multiply(String p1, String p2) {
																					// ;
		int ASCII = 48;
		char[] result = new char[p1.length() + p2.length()];
		for (int i = 0; i < result.length; i++) {
			result[i] = '0';
		}
		char ctemp = ' ';
		//逆序
		char[] pc1 = p1.toCharArray();
		for (int i = 0; i < pc1.length / 2; i++) {
			ctemp = pc1[i];
			pc1[i] = pc1[pc1.length - 1 - i];
			pc1[pc1.length - 1 - i] = ctemp;
		}
		//逆序
		char[] pc2 = p2.toCharArray();
		for (int i = 0; i < pc2.length / 2; i++) {
			ctemp = pc2[i];
			pc2[i] = pc2[pc2.length - 1 - i];
			pc2[pc2.length - 1 - i] = ctemp;
		}
		int temp = 0;// 临时结果
		int step = 0;// 进位
		int time = 0;// 次数
		int bit = 0;// 位数
		for (char c1 : pc1) {
			time = bit;
			for (char c2 : pc2) {
				temp = (c1 - ASCII) * (c2 - ASCII);
				temp = temp + result[time] - ASCII;
				if (temp > 9) {// 进位
					int i = 0;
					do {
						result[time + i] = (char) (temp % 10 + ASCII);
						step = (temp - temp % 10) / 10;
						i++;
						temp = result[time + i] - ASCII + step;
					} while (temp > 9);
					result[time + i] = (char) (temp + ASCII);
				} else {
					result[time] = (char) (temp + ASCII);
				}
				time++;
			}
			bit++;
		}
		System.out.println("##############################");
//		System.out.print(p1 + " x " + p2 + " = ");
		for (int i = result.length - 1; i >= 0; i--) {
			System.out.print(result[i]);
		}
		System.out.println();
		System.out.println("##############################");
	}

}