Externalize unit enumeration and convenience methods.

src/typica.w

@@ -5703,7 +5703,9 @@ temperature and the time at which that measurement was taken.
 
 Measurement times are represented as instances of |QTime|.
 
-The declaration of |Measurement| is reasonably straightforward. Measurements
+@i units.w
+
+@ The declaration of |Measurement| is reasonably straightforward. Measurements
 will often be passed around to a number of different objects through the signals
 and slots mechanism of Qt. The simplest way to make this work is to provide a
 copy constructor and an assignment operator.

src/units.w

@@ -0,0 +1,142 @@
+@* Unit information.
+
+\noindent As unit information is required in several places, the enumeration
+listing these is moved to an external class. This derives from QObject only to
+take advantage of the meta-object system. There are no data members, however
+there are some convenience methods for working with unit data.
+
+@(units.h@>=
+class Units: public QObject
+{
+	Q_OBJECT
+	Q_ENUMS(Units)
+	public:
+		enum Units
+		{
+			Fahrenheit = 10144,
+			Celsius = 10143,
+			Kelvin = 10325,
+			Rankine = 10145
+		};
+		double convertTemperature(double value, Unit fromUnit, Unit toUnit);
+		bool isTemperatureUnit(Unit unit);
+}
+
+@ Methods are implemented in a separate file.
+
+@(units.cpp@>=
+#inculde "units.h"
+#include "moc_units.cpp"
+
+@ The |isTemperatureUnit()| method may seem counter-intuitive while the enum
+only contains represenations of temperature measurements, but there are plans
+to extend this later to extend hardware support to devices that do not directly
+measure temperature values and also to support the measurement of properties
+that cannot sensibly be represented as temperatures such as fuel pressure and
+control settings.
+
+@(units.cpp@>=
+bool Units::isTemperatureUnit(Unit unit)
+{
+	if(unit == Fahrenheit ||
+	   unit == Celsius ||
+	   unit == Kelvin ||
+	   unit == Rankine)
+	{
+		return true;
+	}
+	return false;
+}
+
+@ Temperature conversions can be performed by the |Units| class and should
+eliminate the need to have conversion code in multiple places. This method
+takes the measurement value, the unit that value is in, and the unit that we
+would like to have the measurement converted into. It returns the value as it
+would be expressed after unit conversion. A value of 0 is presently returned
+if either or both of the units to convert are not temperature units, however
+that behavior may change in the future. Any code activating that branch should
+be considered flawed.
+
+@(units.cpp@>=
+double Units::convertTemperature(double value, Unit fromUnit, Unit toUnit)
+{
+	if(isTemperatureUnit(fromUnit) && isTemperatureUnit(toUnit) == false)
+	{
+		return 0;
+	}
+	switch(fromUnit)
+	{
+		case Fahrenheit:
+			switch(toUnit)
+			{
+				case Fahrenheit:
+					return value;
+					break;
+				case Celsius:
+					return (value - 32) * 5 / 9;
+					break;
+				case Kelvin:
+					return (value + 459.67) * 5 / 9;
+					break;
+				case Rankine:
+					return value + 459.67;
+					break;
+			}
+			break;
+		case Celsius:
+			switch(toUnit)
+			{
+				case Fahrenheit:
+					return value * 9 / 5 + 32;
+					break;
+				case Celsius:
+					return value;
+					break;
+				case Kelvin:
+					return value + 273.15;
+					break;
+				case Rankine:
+					return (value + 273.15) * 9 / 5;
+					break;
+			}
+			break;
+		case Kelvin:
+			switch(toUnit)
+			{
+				case Fahrenheit:
+					return value * 5 / 9 - 459.67;
+					break;
+				case Celsius:
+					return value - 273.15;
+					break;
+				case Kelvin:
+					return value;
+					break;
+				case Rankine:
+					return value * 9 / 5;
+					break;
+			}
+			break;
+		case Rankine:
+			switch(toUnit)
+			{
+				case Fahrenheit:
+					return value - 457.67;
+					break;
+				case Celsius:
+					return (value - 491.67) * 5 / 9;
+					break;
+				case Kelvin:
+					return value * 5 / 9;
+					break;
+				case Rankine:
+					return value;
+					break;
+			}
+			break;
+		default:
+			return 0;
+			break;
+	}
+	return 0;
+}