Add degree<->radians conversions for long double and integral types

For long double: they're just missing, so add them for completeness.

For integral types: follow the advice of C11's trigonometric
functions; first convert the angle to double, then do the actual
conversion. This is offered only for the degree->radians conversions,
as someone may legitimately want to call e.g. qDegreesToRadians(90).

On the other hand, it seems extremely unlikely that someone may
want to do a radians->degree conversion starting from integral
datatypes, so I'm not adding it for the moment being (instead,
I'm leaving a note).

[ChangeLog][QtCore][QtMath] qDegreesToRadians now also accepts
long double and integral types. A value of integral type will be
casted to double before the conversion to radians.

[ChangeLog][QtCore][QtMath] qRadiansToDegrees now also accepts
long double.

Change-Id: Ib1576be5193ae09bb6cb4a70d7a31702955df2c5
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qmath.h

@@ -233,6 +233,17 @@ Q_DECL_CONSTEXPR inline double qDegreesToRadians(double degrees)
     return degrees * (M_PI / 180);
 }
 
+Q_DECL_CONSTEXPR inline long double qDegreesToRadians(long double degrees)
+{
+    return degrees * (M_PI / 180);
+}
+
+template <typename T, std::enable_if_t<std::is_integral_v<T>, bool> = true>
+Q_DECL_CONSTEXPR inline double qDegreesToRadians(T degrees)
+{
+    return qDegreesToRadians(static_cast<double>(degrees));
+}
+
 Q_DECL_CONSTEXPR inline float qRadiansToDegrees(float radians)
 {
     return radians * float(180/M_PI);
@@ -243,6 +254,15 @@ Q_DECL_CONSTEXPR inline double qRadiansToDegrees(double radians)
     return radians * (180 / M_PI);
 }
 
+Q_DECL_CONSTEXPR inline long double qRadiansToDegrees(long double radians)
+{
+    return radians * (180 / M_PI);
+}
+
+// A qRadiansToDegrees(Integral) overload isn't here; it's extremely
+// questionable that someone is manipulating quantities in radians
+// using integral datatypes...
+
 namespace QtPrivate {
 constexpr inline quint32 qConstexprNextPowerOfTwo(quint32 v) {
     v |= v >> 1;

src/corelib/kernel/qmath.qdoc

@@ -204,6 +204,30 @@
     \sa qRadiansToDegrees()
 */
 
+/*!
+    \fn long double qDegreesToRadians(long double degrees)
+    \relates <QtMath>
+    \since 6.0
+
+    This function converts the \a degrees in double to radians.
+
+    \sa qRadiansToDegrees()
+*/
+
+/*!
+    \fn template <typename Integral> double qDegreesToRadians(Integral degrees)
+    \relates <QtMath>
+    \since 6.0
+
+    This function converts the \a degrees in double to radians;
+    the angle is casted to a double before the conversion.
+
+    This function participates in overload resolution if and only if
+    \c Integral is an integral type.
+
+    \sa qRadiansToDegrees()
+*/
+
 /*!
     \fn float qRadiansToDegrees(float radians)
     \relates <QtMath>
@@ -232,6 +256,16 @@
     \sa qDegreesToRadians()
 */
 
+/*!
+    \fn long double qRadiansToDegrees(long double radians)
+    \relates <QtMath>
+    \since 6.0
+
+    This function converts the \a radians in double to degrees.
+
+    \sa qDegreesToRadians()
+*/
+
 /*!
     \fn quint32 qNextPowerOfTwo(quint32 value)
     \relates <QtMath>