Added fahrenheit unit (#36)

Co-authored-by: Zachary Levy <zachary@sunforge.is>
Reviewed-on: #36

quantity/temperature.odin

@@ -17,6 +17,11 @@ kelvins_celsius_offset :: #force_inline proc "contextless" (
 	return OFFSET
 }
 
+@(private = "file")
+FAHRENHEIT_PER_CELSIUS_DEGREE :: 9.0 / 5.0
+@(private = "file")
+CELSIUS_PER_FAHRENHEIT_DEGREE :: 5.0 / 9.0
+
 // ---------------------------------------------------------------------------------------------------------------------
 // ----- Types ------------------------
 // ---------------------------------------------------------------------------------------------------------------------
@@ -39,6 +44,13 @@ kelvins_to_deci_kelvins :: #force_inline proc "contextless" (
 	return Deci_Kelvins(V){kelvins.v * DECI}
 }
 
+@(private = "file")
+kelvins_to_fahrenheit :: #force_inline proc "contextless" (
+	kelvins: Kelvins($V),
+) -> Fahrenheit(V) where intrinsics.type_is_numeric(V) {
+	return celsius_to_fahrenheit(kelvins_to_celsius(kelvins))
+}
+
 //----- Decikelvins ----------------------------------
 Deci_Kelvins :: struct($V: typeid) where intrinsics.type_is_numeric(V) {
 	v: V,
@@ -70,6 +82,17 @@ celsius_to_deci_celsius :: #force_inline proc "contextless" (
 	return Deci_Celsius(V){degrees_celsius.v * DECI}
 }
 
+@(private = "file", fast_math = {.Allow_Contract})
+celsius_to_fahrenheit :: #force_inline proc "contextless" (
+	degrees_celsius: Celsius($V),
+) -> Fahrenheit(V) where intrinsics.type_is_numeric(V) {
+	when intrinsics.type_is_float(V) {
+		return Fahrenheit(V){degrees_celsius.v * FAHRENHEIT_PER_CELSIUS_DEGREE + 32.0}
+	} else {
+		return Fahrenheit(V){degrees_celsius.v * 9 / 5 + 32}
+	}
+}
+
 //----- Deci Degrees Celsius ----------------------------------
 Deci_Celsius :: struct($V: typeid) where intrinsics.type_is_numeric(V) {
 	v: V,
@@ -82,12 +105,36 @@ deci_celsius_to_celsius :: #force_inline proc "contextless" (
 	return Celsius(V){deci_degrees_celsius.v / DECI}
 }
 
+//----- Degrees Fahrenheit ----------------------------------
+Fahrenheit :: struct($V: typeid) where intrinsics.type_is_numeric(V) {
+	v: V,
+}
+
+@(private = "file")
+fahrenheit_to_celsius :: #force_inline proc "contextless" (
+	degrees_fahrenheit: Fahrenheit($V),
+) -> Celsius(V) where intrinsics.type_is_numeric(V) {
+	when intrinsics.type_is_float(V) {
+		return Celsius(V){(degrees_fahrenheit.v - 32.0) * CELSIUS_PER_FAHRENHEIT_DEGREE}
+	} else {
+		return Celsius(V){(degrees_fahrenheit.v - 32) * 5 / 9}
+	}
+}
+
+@(private = "file")
+fahrenheit_to_kelvins :: #force_inline proc "contextless" (
+	degrees_fahrenheit: Fahrenheit($V),
+) -> Kelvins(V) where intrinsics.type_is_numeric(V) {
+	return celsius_to_kelvins(fahrenheit_to_celsius(degrees_fahrenheit))
+}
+
 // ---------------------------------------------------------------------------------------------------------------------
 // ----- Conversion Overloads ------------------------
 // ---------------------------------------------------------------------------------------------------------------------
 to_kelvins :: proc {
 	deci_kelvins_to_kelvins,
 	celsius_to_kelvins,
+	fahrenheit_to_kelvins,
 }
 
 to_deci_kelvins :: proc {
@@ -97,12 +144,18 @@ to_deci_kelvins :: proc {
 to_celsius :: proc {
 	kelvins_to_celsius,
 	deci_celsius_to_celsius,
+	fahrenheit_to_celsius,
 }
 
 to_deci_celsius :: proc {
 	celsius_to_deci_celsius,
 }
 
+to_fahrenheit :: proc {
+	celsius_to_fahrenheit,
+	kelvins_to_fahrenheit,
+}
+
 // ---------------------------------------------------------------------------------------------------------------------
 // ----- Tests ------------------------
 // ---------------------------------------------------------------------------------------------------------------------
@@ -155,3 +208,51 @@ test_deci_celsius_to_celsius :: proc(t: ^testing.T) {
 
 	testing.expect_value(t, degrees_celsius, Celsius(int){100})
 }
+
+@(test)
+test_celsius_to_fahrenheit :: proc(t: ^testing.T) {
+	degrees_celsius := Celsius(int){100}
+	degrees_fahrenheit := to_fahrenheit(degrees_celsius)
+
+	testing.expect_value(t, degrees_fahrenheit, Fahrenheit(int){212})
+}
+
+@(test)
+test_fahrenheit_to_celsius :: proc(t: ^testing.T) {
+	degrees_fahrenheit := Fahrenheit(int){212}
+	degrees_celsius := to_celsius(degrees_fahrenheit)
+
+	testing.expect_value(t, degrees_celsius, Celsius(int){100})
+}
+
+@(test)
+test_kelvins_to_fahrenheit :: proc(t: ^testing.T) {
+	kelvins := Kelvins(int){373}
+	degrees_fahrenheit := to_fahrenheit(kelvins)
+
+	testing.expect_value(t, degrees_fahrenheit, Fahrenheit(int){212})
+}
+
+@(test)
+test_fahrenheit_to_kelvins :: proc(t: ^testing.T) {
+	degrees_fahrenheit := Fahrenheit(int){212}
+	kelvins := to_kelvins(degrees_fahrenheit)
+
+	testing.expect_value(t, kelvins, Kelvins(int){373})
+}
+
+@(test)
+test_celsius_to_fahrenheit_f64 :: proc(t: ^testing.T) {
+	// -40 is the point where the Celsius and Fahrenheit scales coincide. It converts exactly in
+	// f64, so a passing equality here also confirms the 9/5 ratio constant is not lossy.
+	degrees_fahrenheit := to_fahrenheit(Celsius(f64){-40})
+
+	testing.expect_value(t, degrees_fahrenheit, Fahrenheit(f64){-40})
+}
+
+@(test)
+test_fahrenheit_to_celsius_f64 :: proc(t: ^testing.T) {
+	degrees_celsius := to_celsius(Fahrenheit(f64){-40})
+
+	testing.expect_value(t, degrees_celsius, Celsius(f64){-40})
+}