copysignx

Copysignx is a function used in some programming libraries to produce a value with the magnitude of the first argument and the sign of the second argument. It is conceptually identical to the standard copysign function found in C and many math libraries, but some libraries expose an explicit copysignx name or provide a type-generic wrapper under that name. It is not universally part of the C standard library, and its availability depends on the language and implementation.

In typical C- or C++-oriented libraries, the function exists in type-specific and generic forms. Common prototypes (or their equivalents through templates or overloading) include:

- double copysignx(double x, double y)

- float copysignxf(float x, float y)

- long double copysignxl(long double x, long double y)

Semantics and behavior:

- The function returns a value whose magnitude is |x| and whose sign equals the sign of y. In other words, the result is abs(x) with the sign of y.

- Sign determination uses the sign bit of y, including distinction of positive and negative zero when applicable.

- If x is NaN or y is NaN, many implementations propagate a NaN result with the sign determined by y, mirroring the behavior of copysign. For zeros, copilots may yield positive or negative zero depending on the sign of y.

Examples:

- copysignx(3.0, -2.0) yields -3.0.

- copysignx(-0.0, 1.0) yields 0.0 (positive zero).

- copysignx(5.0, NaN) yields a NaN with the sign dictated by the NaN’s sign bit.

See also: copysign, copysignf, copysignl, signbit, fabs.