Java Array Multiply multiply(byte[] a, byte b)

Description

a * b

License

Open Source License

Parameter

Parameter	Description
a	a parameter
b	a parameter

Declaration

public static byte[] multiply(byte[] a, byte b) 

Method Source Code

//package com.java2s;
/**//from  ww  w .  j  a v  a2s . co m
 * ?????????? unsigned ????????????????????????????????????????
 *
 * License : MIT License
 */

public class Main {
    /**
     * a * b
     * @param a
     * @param b
     * @return
     */
    public static byte[] multiply(byte[] a, byte b) {
        if (a == null)
            throw new IllegalArgumentException("a should not be null");

        int len = a.length;
        byte[] result = new byte[len];
        int carry = 0;
        int i2 = byte2int(b);
        for (int i = len - 1; 0 <= i; i--) {
            int i1 = byte2int(a[i]); // 0 <= i1 <= 255(0xff)
            int col = i1 * i2 + carry;
            carry = (col >> 8);
            result[i] = int2byte(col);
        }
        return result;
    }

    /**
     * a * b
     * @param a
     * @param b
     * @return
     */
    public static byte[] multiply(byte[] a, byte[] b) {
        if (a == null)
            throw new IllegalArgumentException("a should not be null");
        if (b == null)
            throw new IllegalArgumentException("b should not be null");
        if (a.length != b.length)
            throw new IllegalArgumentException(
                    "byte array length should be same");

        int len = a.length;
        byte[] result = new byte[len];
        for (int offset = len - 1; 0 <= offset; offset--) {
            int i2 = byte2int(b[offset]); // 0 <= i1 <= 255(0xff)
            int carry = 0;
            for (int i = len - 1; 0 <= i; i--) {
                int pos = offset - (len - 1 - i);
                if (pos < 0)
                    break;
                int i1 = byte2int(a[i]); // 0 <= i1 <= 255(0xff)
                int r = byte2int(result[pos]);
                int col = r + i1 * i2 + carry;
                carry = (col >> 8);
                result[pos] = int2byte(col);
            }
        }
        return result;
    }

    public static int byte2int(byte b) {
        return ((int) b & 0x000000ff);
    }

    public static byte int2byte(int i) {
        return (byte) (i & 0x000000ff);
    }
}

Related

1. mult(double[][] A, double[][] B)
2. mult(float[] nums, float n)
3. mult(float[] nums, float n)
4. multiply(double factor, double[] vector)
5. multiply(double[] a, double m)
6. multiply(double[] a, double v)
7. multiply(double[] a, double[] b)