fdim() Function in C

Introduction

The fdim() function is also a part of C Standard Library included in the C programming language and defined in the <math.h> header file. The abbreviation for floating-point difference, the fdim() function is used to compute the positive difference between two floating-point operands. In other words, it gives the difference of two values if the first value is larger than the second one; otherwise, it returns a zero. Learning about fdim() will assist in the enhancement of the levels of accuracy and efficiency in mathematical and scientific applications that contain floating point computations.

Syntax of fdim():

 
#include <math.h>
double fdim(double x, double y);
float fdimf(float x, float y);
long double fdiml(long double x, long double y);   

Where,

fdim(double x, double y)- This function computes the positive difference between two double values x and y.
fdimf(float x, float y)- This function computes the positive difference between two float values x and y.
fdiml(long double x, long double y)- This function computes the positive difference between two long double values x and y.

Note: In each case, if x > y, the function returns x - y; otherwise, it returns 0.0.

Return Value of fdim()

The return value of the fdim() function depends on the comparison between the two input arguments, x and y. Here are the possible outcomes:

If x is greater than y, The function returns the positive difference: x - y.
If x is less than or equal to y, The function returns 0.0.

The return type of the function matches the type of the input parameters:

The return type is double for fdim(double x, double y).
The return type is float for fdimf(float x, float y).
The return type is long double for fdiml(long double x, long double y).

Examples of fdim()

Case 1:

x is greater than y

 
Output: 6.3

Case 2:

x is less than or equal to y

 
Output: 0.0

Example 1:

Let us take a C program to demonstrate the fdim() function.

 
#include <math.h>
#include <stdio.h>

int main()
{
    // declare and initialize variables
    double num1 = 8.7, num2 = 6.4;
    // compute positive difference using fdim() function
    double posDiff = fdim(num1, num2);

    // Print the positive difference
    printf("The positive difference between %.2lf and "
           "%.2lf is: %.2lf\n",
           num1, num2, posDiff);

    return 0;
}   

Output:

 
The positive difference between 8.70 and 6.40 is: 2.30

Example 2:

Let us take a C program to demonstrate the fdim() function for various floating-point types.

 
#include <math.h>
#include <stdio.h>

int main()
{
    // declare and initialize variables
    double num1 = 8.5, num2 = 4.3;
    float num3 = 9.6f, num4 = 2.5f;
    long double num5 = 10.7l, num6 = 3.4l;

    // compute positive difference using fdim() for double
    double diff1 = fdim(num1, num2);

    // compute positive difference using fdimf() for float
    float diff2 = fdimf(num3, num4);

    // compute positive difference using fdiml() for long double
    long double diff3 = fdiml(num5, num6);

    // Print the positive differences
    printf("The positive difference between %.2lf and "
           "%.2lf is: %.2lf\n",
           num1, num2, diff1);
    printf("The positive difference between %.2f and %.2f "
           "is: %.2f\n",
           num3, num4, diff2);
    printf("The positive difference between %.2Lf and "
           "%.2Lf is: %.2Lf\n",
           num5, num6, diff3);

    return 0;
}   

Output:

 
The positive difference between 8.50 and 4.30 is: 4.20
The positive difference between 9.60 and 2.50 is: 7.10
The positive difference between 10.70 and 3.40 is: 7.30

Features of fdim()

Positive Difference Calculation:
The principal purpose of fdim() intrinsic function is to return the positive difference of two floating-point numbers. When x > y, it returns x - y; otherwise, if x <= y, it returns 0.
Support for Different Floating-Point Types:
The function is generic for floating point type; raises remainder of 'a' to single precision float, 'b' to double precision double, and 'c' to long double using fdim(), fdimf(), and fdiml() respectively. This makes it possible according to the need of the application in terms of the degree of precision.
Mathematical Precision:
Again, in computing the positive difference, fdim() guarantees the accurate and correct computation to meet numerous mathematical and scientific processes where the negative discrepancies cannot be embraced.
Portability:
Thus, since fdim() is a part of the C Standard Library and declared in <math. h>, it is not sensitive to the platform or compiler that does not conform to the C standard.
Error Handling:
The function can handle rather specific values of the floating-point type, particularly NaN (Not a Number) and Infinity. If either of the parameters x or y is a NaN, then the operation's result is also NaN. If x and the variable are positive infinity and y is finite, the resulting value is positive infinity.
Efficient Implementation:
Implemented efficiently inside standard libraries, fdim() is used for precise positive difference calculations, and it is designed for the application's required efficiency, sometimes using function creation.

Drawbacks of fdim()

Limited Use Case:
The fdim() is a function that only computes the positive difference between two numbers. However, it is less general than the other arithmetic functions because the absolute value cannot be used directly for negative differences and general subtraction.
Handling of Special Values:
As for NaN and Infinity, fdim() deals with them, but the action may be quite unexpected. For example, if one of the inputs is NaN, then the result of the % operator is also NaN, which may sometimes need special checks in the code.
Lack of Integer Support:
The fdim() function is only appropriate for the floating-point numbers alone. It does not include the integer type; hence, any integer is required to be converted or cast into a floating point type before it can be passed to fdim(), which may lead to loss of precision or added computational process.
Potential for Misuse:
The user could misinterpret the function objectives and may use extract when a subtraction would suffice or a subtraction where an extract should be made, and therefore mislead himself.
Performance Considerations:
Although the function is efficient, it entails an 'if …else..' construction to test for the conditions in which to return the difference or zero. In general, applications where these operations are performed frequently, and even small overhead can add up.
Standard Library Dependency:
Being a part of the C Standard Library, the fdim() function means that including <math. h>. This dependency might not be desirable usually, especially in specific scenarios where the use of libraries needs to be restricted as much as possible.
Compiler and Platform Variations:
The results and performance of fdim() may differ with respect to the compiler and the platform and, as a result, may be inconsistent.

Conclusion:

The fdim() function in C is a specific function used for a specific computing operation of positive differences between two floating point numbers. Defined in the <math. This is done in the form of returning the result of the operation as an unsigned char in the case where the header file is concerned, and this makes the result of the operation always non-negative; this can prove to be useful in many circumstances, including mathematical and scientific computations. The function supports double, float, and long double types of floating-point numbers meant for different levels of precision.

In general, fdim() can be considered a very useful function, with the following small discrepancies. As mentioned earlier, it is mainly used for positive difference calculations. It is not a supporter of integer-type values. However, working with special values, such as NaN and Infinity, might need further work, and it is dependent on C Standard Library, which might not always be suitable. Further, as for the conditional expressions used in the function's implementation, although flexible and straightforward, they may add subtle extra costs to the performance-sensitive application.

In conclusion, it is beneficial to get familiar with the effectiveness and ineffectively of employing the fdim() since the developers, having an efficient knowledge of the existing function along with its disadvantages, will be able to write an efficient code that will offer a correct and positive variation solution in the situations where it is a necessity.

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