C++ Program to Implement the Schonhage-Strassen Algorithm for Multiplication of Two Numbers

This is a C++ Program to implement Schonhage-Strassen algorithm to multiply two numbers.

Here is source code of the C++ Program to Implement the Schonhage-Strassen Algorithm for Multiplication of Two Numbers. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

```
#include <iostream>
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```
 
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using namespace std;
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```
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int noOfDigit(long a)
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```
{
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    int n = 0;
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    while (a > 0)
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    {
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        a /= 10;
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        n++;
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    }
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    return n;
```
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}
```

void schonhageStrassenMultiplication(long x, long y, int n, int m)

```
{
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```
 
```
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    int linearConvolution[n + m - 1];
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    for (int i = 0; i < (n + m - 1); i++)

```
        linearConvolution[i] = 0;
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```
 
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    long p = x;
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    for (int i = 0; i < m; i++)
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    {
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        x = p;
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        for (int j = 0; j < n; j++)
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        {
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            linearConvolution[i + j] += (y % 10) * (x % 10);

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            x /= 10;
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        }
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        y /= 10;
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    }
```

    cout << "The Linear Convolution is: ( ";

    for (int i = (n + m - 2); i >= 0; i--)

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    {
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        cout << linearConvolution[i] << " ";

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    }
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    cout << ")";
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    long product = 0;
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    int nextCarry = 0, base = 1;
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    ;
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    for (int i = 0; i < n + m - 1; i++)
```
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    {
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        linearConvolution[i] += nextCarry;

        product = product + (base * (linearConvolution[i] % 10));

        nextCarry = linearConvolution[i] / 10;

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        base *= 10;
```
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    }
```

    cout << "\nThe Product of the numbers is: " << product;

```
 
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}
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int main(int argc, char **argv)
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{
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    cout << "Enter the numbers:";
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    long a, b;
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    cin >> a >> b;
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    int n = noOfDigit(a);
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    int m = noOfDigit(b);
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    schonhageStrassenMultiplication(a, b, n, m);

```
}
```

Output:

$ g++ Schonhage-StrassenAlgorithm.cpp
$ a.out
 
Enter the numbers:3452 1245
The Linear Convolution is: ( 3 10 25 43 44 33 10 )
 Product of the numbers is: 4297740

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