Does C/C Have a Standard Sign Function for Floating-Point Numbers?

Is There a Standard Sign Function in C/C ?

Question:

I am seeking a function that outputs -1 for negative numbers and 1 for positive numbers. Despite its simplicity, I suspect this functionality may be available in a standard library somewhere. Specifically, I require a function that operates on float data types.

Answer:

Yes, there is a standard C function that serves this purpose, known as signum. However, it is important to note that this function is type-safe, meaning it can operate on various data types, not just floats. Here's a generic implementation of signum:

template <typename T>
int sgn(T val) {
    return (T(0) < val) - (val < T(0));
}

This function offers several advantages over custom implementations:

• Accurate Signum Implementation: It renders -1 for negative numbers, 0 for zero, and 1 for positive numbers.
• Type Versatility: It can operate on integers, floats, doubles, and various other data types.
• Efficiency: The branchless implementation utilizes compiler optimization for exceptional performance.

Usage:

int sign = sgn(-1.5); // -1
sign = sgn(0.0);      // 0
sign = sgn(3.14);     // 1

Caveats:

• Compilation Time: As a template, it may incur a longer compilation time in certain scenarios.
• Unconventional Syntax: Some may prefer the use of copysign as it is a standard library function, even though it does not accurately implement the sign function.
• Warning Triggering: If used with unsigned types, it can trigger the "-Wtype-limits" warning in GCC. To address this, you can employ template specialization with overloads.

In conclusion, the signum function provides a versatile and efficient solution for determining the sign of a number in C . While it may not be directly available for floats in the standard library, its type-safe implementation enables its use on a wide range of data types with remarkable accuracy.

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