programming-examples/c/Numerical/C Program to Implement Booth’s Multiplication Algorithm for Multiplication of 2 signed Numbers.c

#include <stdio.h>
#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]);
        }
}
void arshift() //for arithmetic shift right
{
    int temp = pro[4], temp2 = pro[0], i;
    for (i = 1; i < 5  ; i++) //shift the MSB of product
        {
            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]);
        }
}

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