Ceiling(NaN()) causes an overflow

[weucode]

Describe the bug
The result of Lg with a non-positive parameter is NaN, so running the following program will cause overflow. The part of the output is shown below:

Unhandled exception. System.OverflowException: Arithmetic operation resulted in an overflow.

To Reproduce

namespace NameSpace {
	open Microsoft.Quantum.Intrinsic;
	open Microsoft.Quantum.Math;


	@EntryPoint()
	operation main() : Unit {
		let nIdxRegQubits = Ceiling(Lg(-1.0));
		// same as:let nIdxRegQubits = Ceiling(NaN());
		Message($"{nIdxRegQubits}");
	}
}

Expected behavior
Maybe a range check can be used to avoid it.

System information
operating system : Ubuntu 22.04 LTS

dotnet version : 6.0.400

QDK : 0.25.228311

[weucode]

It seems this API effect other APIs, one can be seen in microsoft/QuantumLibraries#570; if give targetError a value of 0.0, an overflow behavior will occur. It might be better to fix Ceiling rather than other high-level APIs.

[msoeken]

Thanks @weucode for filing this. It would be better to return NaN in this case. The function is implemented in Microsoft/qsharp-runtime (see

qsharp-runtime/src/Simulation/QSharpFoundation/Math/Math.qs

Line 506 in 15a5493

function Ceiling(value : Double) : Int {

), so I am transferring the issue to that repository.