Booths_algo.cpp

// Booths Algorithm

#include <iostream>
#include <math.h>

int a = 0, b = 0, c = 0, a1 = 0, b1 = 0, com[5] = {1, 0, 0, 0, 0};
int anum[5] = {0}, anumcp[5] = {0}, bnum[5] = {0};
int acomp[5] = {0}, bcomp[5] = {0}, pro[5] = {0}, res[5] = {0};

void binary()
{
    a1 = fabs(a);
    b1 = fabs(b);
    int r, r2, i, temp;

    for (i = 0; i < 5; i++)
    {
        r = a1 % 2;
        a1 = a1 / 2;
        r2 = b1 % 2;
        b1 = b1 / 2;

        anum[i] = r;
        anumcp[i] = r;
        bnum[i] = r2;

        if (r2 == 0)
            bcomp[i] = 1;
        if (r == 0)
            acomp[i] = 1;
    }

    // part for two's complementing
    c = 0;
    for (i = 0; i < 5; i++)
    {
        res[i] = com[i] + bcomp[i] + c;
        if (res[i] >= 2)
            c = 1;
        else
            c = 0;

        res[i] = res[i] % 2;
    }

    for (i = 4; i >= 0; i--)
        bcomp[i] = res[i];

    // in case of negative inputs
    if (a < 0)
    {
        c = 0;
        for (i = 4; i >= 0; i--)
            res[i] = 0;

        for (i = 0; i < 5; i++)
        {
            res[i] = com[i] + acomp[i] + c;
            if (res[i] >= 2)
                c = 1;
            else
                c = 0;

            res[i] = res[i] % 2;
        }

        for (i = 4; i >= 0; i--)
        {
            anum[i] = res[i];
            anumcp[i] = res[i];
        }
    }

    if (b < 0)
    {
        for (i = 0; i < 5; i++)
        {
            temp = bnum[i];
            bnum[i] = bcomp[i];
            bcomp[i] = temp;
        }
    }
}

void add(int num[])
{
    int i;
    c = 0;

    for (i = 0; i < 5; i++)
    {
        res[i] = pro[i] + num[i] + c;
        if (res[i] >= 2)
            c = 1;
        else
            c = 0;

        res[i] = res[i] % 2;
    }

    for (i = 4; i >= 0; i--)
    {
        pro[i] = res[i];
        printf("%d", pro[i]);
    }
    printf(" : ");
    for (i = 4; i >= 0; i--)
        printf("%d", anumcp[i]);
}

// for arithmetic shift right
void arshift()
{
    int temp = pro[4], temp2 = pro[0], i;

    // shift the MSB of product
    for (i = 1; i < 5; i++)
        pro[i - 1] = pro[i];

    pro[4] = temp;
    for (i = 1; i < 5; i++)
        // shift the LSB of product
        anumcp[i - 1] = anumcp[i];

    anumcp[4] = temp2;
    printf("\nAR-SHIFT: "); // display together
    for (i = 4; i >= 0; i--)
        printf("%d", pro[i]);

    printf(" : ");
    for (i = 4; i >= 0; i--)
    {
        printf("%d", anumcp[i]);
    }
}

int main()
{
    int i, q = 0;
    printf("\t\tBOOTH'S MULTIPLICATION ALGORITHM");
    printf("\nEnter two numbers to multiply: ");
    printf("\nBoth must be less than 16");
    // simulating for two numbers each below 16
    do
    {
        printf("\nEnter A: ");
        scanf("%d", &a);
        printf("Enter B: ");
        scanf("%d", &b);
    } while (a >= 16 || b >= 16);

    printf("\nExpected product = %d", a * b);
    binary();
    printf("\n\nBinary Equivalents are: ");
    printf("\nA = ");
    for (i = 4; i >= 0; i--)
    {
        printf("%d", anum[i]);
    }
    printf("\nB = ");
    for (i = 4; i >= 0; i--)
    {
        printf("%d", bnum[i]);
    }
    printf("\nB'+ 1 = ");
    for (i = 4; i >= 0; i--)
    {
        printf("%d", bcomp[i]);
    }
    printf("\n\n");
    for (i = 0; i < 5; i++)
    {
        if (anum[i] == q)
        { // just shift for 00 or 11
            printf("\n-->");
            arshift();
            q = anum[i];
        }
        else if (anum[i] == 1 && q == 0)
        { // subtract and shift for 10
            printf("\n-->");
            printf("\nSUB B: ");
            add(bcomp); // add two's complement to implement subtraction
            arshift();
            q = anum[i];
        }
        else
        { // add ans shift for 01
            printf("\n-->");
            printf("\nADD B: ");
            add(bnum);
            arshift();
            q = anum[i];
        }
    }

    printf("\nProduct: ");
    for (i = 4; i >= 0; i--)
    {
        printf("%d", pro[i]);
    }
    for (i = 4; i >= 0; i--)
    {
        printf("%d", anumcp[i]);
    }
}