programming-examples/java/Numerical_Problems/Java Program to Implement Booth Algorithm.java

/*
This is a Java Program to implement Booth Algorithm. This is a program to compute product of two numbers by using Booth’s Algorithm. This program is implemented for multiplying numbers in the range -7 to 7. However same principle can be extended to other numbers too.
*/

/**
 ** Java Program to Implement Booth Algorithm
 **/

import java.util.Scanner;

/** Class Booth **/
public class Booth
{
    public static Scanner s = new Scanner(System.in);
    /** Function to multiply **/
    public int multiply(int n1, int n2)
    {
        int[] m = binary(n1);
        int[] m1 = binary(-n1);
        int[] r = binary(n2);
        int[] A = new int[9];
        int[] S = new int[9];
        int[] P = new int[9];
        for (int i = 0; i < 4; i++)
            {
                A[i] = m[i];
                S[i] = m1[i];
                P[i + 4] = r[i];
            }
        display(A, 'A');
        display(S, 'S');
        display(P, 'P');
        System.out.println();
        for (int i = 0; i < 4; i++)
            {
                if (P[7] == 0 && P[8] == 0);
                // do nothing
                else if (P[7] == 1 && P[8] == 0)
                    add(P, S);
                else if (P[7] == 0 && P[8] == 1)
                    add(P, A);
                else if (P[7] == 1 && P[8] == 1);
                // do nothing
                rightShift(P);
                display(P, 'P');
            }
        return getDecimal(P);
    }
    /** Function to get Decimal equivalent of P **/
    public int getDecimal(int[] B)
    {
        int p = 0;
        int t = 1;
        for (int i = 7; i >= 0; i--, t *= 2)
            p += (B[i] * t);
        if (p > 64)
            p = -(256 - p);
        return p;
    }
    /** Function to right shift array **/
    public void rightShift(int[] A)
    {
        for (int i = 8; i >= 1; i--)
            A[i] = A[i - 1];
    }
    /** Function to add two binary arrays **/
    public void add(int[] A, int[] B)
    {
        int carry = 0;
        for (int i = 8; i >= 0; i--)
            {
                int temp = A[i] + B[i] + carry;
                A[i] = temp % 2;
                carry = temp / 2;
            }
    }
    /** Function to get binary of a number **/
    public int[] binary(int n)
    {
        int[] bin = new int[4];
        int ctr = 3;
        int num = n;
        /** for negative numbers 2 complment **/
        if (n < 0)
            num = 16 + n;
        while (num != 0)
            {
                bin[ctr--] = num % 2;
                num /= 2;
            }
        return bin;
    }
    /** Function to print array **/
    public void display(int[] P, char ch)
    {
        System.out.print("\n"+ ch +" : ");
        for (int i = 0; i < P.length; i++)
            {
                if (i == 4)
                    System.out.print(" ");
                if (i == 8)
                    System.out.print(" ");
                System.out.print(P[i]);
            }
    }
    /** Main function **/
    public static void main (String[] args)
    {
        Scanner scan = new Scanner(System.in);
        System.out.println("Booth Algorithm Test\n");
        /** Make an object of Booth class **/
        Booth b = new Booth();
        /** Accept two integers **/
        System.out.println("Enter two integer numbers\n");
        int n1 = scan.nextInt();
        int n2 = scan.nextInt();
        int result = b.multiply(n1, n2);
        System.out.println("\n\nResult : "+ n1 +" * "+ n2 +" = "+ result);
    }
}

/*

Enter two integer numbers

7 -7

A : 0111 0000 0
S : 1001 0000 0
P : 0000 1001 0

P : 1100 1100 1
P : 0001 1110 0
P : 0000 1111 0
P : 1100 1111 1

Result : 7 * -7 = -49