c/numeric/math/copysign

@1-3@ Composes a floating point value with the magnitude of and the sign of. @4@ Type-generic macro: If any argument has type, is called. Otherwise, if any argument has integer type or has type, is called. Otherwise, is called.

Return value
If no errors occur, the floating point value with the magnitude of and the sign of  is returned.

If is NaN, then NaN with the sign of  is returned.

If is -0, the result is only negative if the implementation supports the signed zero consistently in arithmetic operations.

Error handling
This function is not subject to any errors specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),
 * The returned value is exact (fe_inexact is never raised) and independent of the current rounding mode.