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Last Updated: Mar 27, 2024
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fma() Function in C++

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Prerita Agarwal
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23 Jul, 2024 @ 01:30 PM

Introduction

In computer programming, precision matters. When working with floating-point operations, precision can be especially important. This is where the fma() function in C++ comes into play. 

fma() function in C++

The fma() function, which stands for Fused Multiply-Add, is used to perform high-precision multiplication and addition operations.

Understanding fma()

The fma() function multiplies two floating-point values and then adds a third, all in one operation. This function can be found in the <cmath> library in C++. The combined operation is more precise than performing the multiplication and addition separately. Here is its basic syntax:

double fma(double x, double y, double z);

The function takes three parameters:

x and y are the numbers to be multiplied.

z is the number to be added to the product of x and y.

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Using fma()

Let's look at a simple example of how fma() is used:

#include <iostream>
#include <cmath>


int main() {
    double result = std::fma(2.0, 3.0, 4.0);
    std::cout << "The result is: " << result;
    return 0;
}

In the above example, 2.0 is multiplied by 3.0, and then 4.0 is added. The output would be 10.0.

Output 

Output

Precision of fma()

So, why use fma() when you can perform multiplication and addition separately? The answer lies in precision. Let's look at an example:

#include <iostream>
#include <cmath>


int main() {
    double a = 1e16, b = 3.14159, c = -1e16;
    double result = std::fma(a, b, c);
    std::cout << "The fma result is: " << result << '\n';
    result = a * b + c;
    std::cout << "The regular result is: " << result;
    return 0;
}

Output 

Output

In this case, the fma() function provides a more precise result than the separate operations.

Real World Applications

The fma() function is essential in fields where high precision is required, such as physics simulations, graphics rendering, and financial calculations. Its ability to maintain precision can be crucial to the accuracy of these operations.

Frequently Asked Questions 

What does the fma() function in C++ do?

The fma() function performs a multiplication operation and an addition operation in one step, providing a more precise result.

Why would you use fma() instead of performing multiplication and addition separately?

Using fma() can provide a more precise result, especially for very large or very small numbers.

What are some applications of the fma() function?

fma() is used in fields requiring high precision, such as physics simulations, graphics rendering, and financial calculations.

Conclusion

The fma() function in C++ provides a valuable tool for performing high-precision multiplication and addition operations. By fusing these operations into one function, it can deliver more accurate results, especially when dealing with large or small numbers. Understanding and applying fma() can significantly enhance the accuracy of calculations in your C++ programs.

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Topics covered
1.
Introduction
2.
Understanding fma()
3.
Using fma()
3.1.
Precision of fma()
4.
Real World Applications
5.
Frequently Asked Questions 
5.1.
What does the fma() function in C++ do?
5.2.
Why would you use fma() instead of performing multiplication and addition separately?
5.3.
What are some applications of the fma() function?
6.
Conclusion