Name newBase, not x, when Log is given a base outside its domain [patch]

PreciseNumber.Test/PreciseNumberExponentialTests.cs

@@ -142,6 +142,28 @@ public void TestLogRejectsValuesOutsideItsDomain()
 		Assert.ThrowsExactly<ArgumentOutOfRangeException>(() => PreciseNumber.Log(2.ToPreciseNumber(), 0));
 	}
 
+	[TestMethod]
+	public void TestLogInABaseNamesTheArgumentOutsideTheDomain()
+	{
+		// The base is passed on to the single-argument Log, whose guard names x, so each argument has
+		// to be checked under its own name first.
+		ArgumentOutOfRangeException negativeBase = Assert.ThrowsExactly<ArgumentOutOfRangeException>(
+			() => PreciseNumber.Log(5.ToPreciseNumber(), (-2).ToPreciseNumber()));
+		Assert.AreEqual("newBase", negativeBase.ParamName);
+		Assert.AreEqual((-2).ToPreciseNumber(), negativeBase.ActualValue);
+
+		ArgumentOutOfRangeException zeroBase = Assert.ThrowsExactly<ArgumentOutOfRangeException>(
+			() => PreciseNumber.Log(5.ToPreciseNumber(), PreciseNumber.Zero, 20));
+		Assert.AreEqual("newBase", zeroBase.ParamName);
+
+		ArgumentOutOfRangeException negativeValue = Assert.ThrowsExactly<ArgumentOutOfRangeException>(
+			() => PreciseNumber.Log((-5).ToPreciseNumber(), 2.ToPreciseNumber()));
+		Assert.AreEqual("x", negativeValue.ParamName);
+
+		// A base of one is still a division by its zero logarithm.
+		Assert.ThrowsExactly<DivideByZeroException>(() => PreciseNumber.Log(5.ToPreciseNumber(), PreciseNumber.One));
+	}
+
 	[TestMethod]
 	public void TestExpMatchesPublishedDigits()
 	{

PreciseNumber/PreciseNumber.Exponentials.cs

@@ -192,6 +192,19 @@ public static PreciseNumber Log(PreciseNumber x, PreciseNumber newBase) =>
 	public static PreciseNumber Log(PreciseNumber x, PreciseNumber newBase, int significantDigits)
 	{
 		RequireSignificantDigits(significantDigits);
+
+		// Each argument is checked under its own name before either logarithm is worked out, so a bad
+		// base is not reported as a bad value by the single-argument Log it would otherwise reach.
+		if (x.Significand.Sign <= 0)
+		{
+			throw new ArgumentOutOfRangeException(nameof(x), x, NonPositiveLogarithmMessage);
+		}
+
+		if (newBase.Significand.Sign <= 0)
+		{
+			throw new ArgumentOutOfRangeException(nameof(newBase), newBase, NonPositiveLogarithmMessage);
+		}
+
 		int working = significantDigits + ExponentialGuardDigits;
 		return DivideApproximation(Log(x, working), Log(newBase, working), working, significantDigits);
 	}