Add inverse hyperbolic functions asinh(), acosh() & atanh()

GDScript has the following built-in trigonometry functions: - `sin()` - `cos()` - `tan()` - `asin()` - `acos()` - `atan()` - `atan()` - `sinh()` - `cosh()` - `tanh()` However, it lacks the hyperbolic arc (also known as inverse hyperbolic) functions: - `asinh()` - `acosh()` - `atanh()` Implement them by just exposing the C++ Math library, but clamping its values to the closest real defined value. For the cosine, clamp input values lower than 1 to 1. In the case of the tangent, where the limit value is infinite, clamp it to -inf or +inf. References #78377 Fixes godotengine/godot-proposals#7110
godotengine · Aug 31, 2023 · 528a764 · 528a764
1 parent 549fcce
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diff --git a/core/math/math_funcs.h b/core/math/math_funcs.h
@@ -88,6 +88,17 @@ class Math {
 	static _ALWAYS_INLINE_ double atan2(double p_y, double p_x) { return ::atan2(p_y, p_x); }
 	static _ALWAYS_INLINE_ float atan2(float p_y, float p_x) { return ::atan2f(p_y, p_x); }
 
+	static _ALWAYS_INLINE_ double asinh(double p_x) { return ::asinh(p_x); }
+	static _ALWAYS_INLINE_ float asinh(float p_x) { return ::asinhf(p_x); }
+
+	// Always does clamping so always safe to use.
+	static _ALWAYS_INLINE_ double acosh(double p_x) { return p_x < 1 ? 0 : ::acosh(p_x); }
+	static _ALWAYS_INLINE_ float acosh(float p_x) { return p_x < 1 ? 0 : ::acoshf(p_x); }
+
+	// Always does clamping so always safe to use.
+	static _ALWAYS_INLINE_ double atanh(double p_x) { return p_x <= -1 ? -INFINITY : (p_x >= 1 ? INFINITY : ::atanh(p_x)); }
+	static _ALWAYS_INLINE_ float atanh(float p_x) { return p_x <= -1 ? -INFINITY : (p_x >= 1 ? INFINITY : ::atanhf(p_x)); }
+
 	static _ALWAYS_INLINE_ double sqrt(double p_x) { return ::sqrt(p_x); }
 	static _ALWAYS_INLINE_ float sqrt(float p_x) { return ::sqrtf(p_x); }
 

diff --git a/core/variant/variant_utility.cpp b/core/variant/variant_utility.cpp
@@ -81,6 +81,18 @@ double VariantUtilityFunctions::atan2(double y, double x) {
 	return Math::atan2(y, x);
 }
 
+double VariantUtilityFunctions::asinh(double arg) {
+	return Math::asinh(arg);
+}
+
+double VariantUtilityFunctions::acosh(double arg) {
+	return Math::acosh(arg);
+}
+
+double VariantUtilityFunctions::atanh(double arg) {
+	return Math::atanh(arg);
+}
+
 double VariantUtilityFunctions::sqrt(double x) {
 	return Math::sqrt(x);
 }
@@ -1502,6 +1514,10 @@ void Variant::_register_variant_utility_functions() {
 
 	FUNCBINDR(atan2, sarray("y", "x"), Variant::UTILITY_FUNC_TYPE_MATH);
 
+	FUNCBINDR(asinh, sarray("x"), Variant::UTILITY_FUNC_TYPE_MATH);
+	FUNCBINDR(acosh, sarray("x"), Variant::UTILITY_FUNC_TYPE_MATH);
+	FUNCBINDR(atanh, sarray("x"), Variant::UTILITY_FUNC_TYPE_MATH);
+
 	FUNCBINDR(sqrt, sarray("x"), Variant::UTILITY_FUNC_TYPE_MATH);
 	FUNCBINDR(fmod, sarray("x", "y"), Variant::UTILITY_FUNC_TYPE_MATH);
 	FUNCBINDR(fposmod, sarray("x", "y"), Variant::UTILITY_FUNC_TYPE_MATH);

diff --git a/core/variant/variant_utility.h b/core/variant/variant_utility.h
@@ -45,6 +45,9 @@ struct VariantUtilityFunctions {
 	static double acos(double arg);
 	static double atan(double arg);
 	static double atan2(double y, double x);
+	static double asinh(double arg);
+	static double acosh(double arg);
+	static double atanh(double arg);
 	static double sqrt(double x);
 	static double fmod(double b, double r);
 	static double fposmod(double b, double r);

diff --git a/doc/classes/@GlobalScope.xml b/doc/classes/@GlobalScope.xml
@@ -72,6 +72,19 @@
 				[/codeblock]
 			</description>
 		</method>
+		<method name="acosh">
+			<return type="float" />
+			<param index="0" name="x" type="float" />
+			<description>
+				Returns the hyperbolic arc (also called inverse) cosine of [param x], returning a value in radians. Use it to get the angle from an angle's cosine in hyperbolic space if [param x] is larger or equal to 1. For values of [param x] lower than 1, it will return 0, in order to prevent [method acosh] from returning [constant @GDScript.NAN].
+				[codeblock]
+				var a = acosh(2) # Returns 1.31695789692482
+				cosh(a) # Returns 2
+
+				var b = acosh(-1) # Returns 0
+				[/codeblock]
+			</description>
+		</method>
 		<method name="asin">
 			<return type="float" />
 			<param index="0" name="x" type="float" />
@@ -83,6 +96,17 @@
 				[/codeblock]
 			</description>
 		</method>
+		<method name="asinh">
+			<return type="float" />
+			<param index="0" name="x" type="float" />
+			<description>
+				Returns the hyperbolic arc (also called inverse) sine of [param x], returning a value in radians. Use it to get the angle from an angle's sine in hyperbolic space.
+				[codeblock]
+				var a = asinh(0.9) # Returns 0.8088669356527824
+				sinh(a) # Returns 0.9
+				[/codeblock]
+			</description>
+		</method>
 		<method name="atan">
 			<return type="float" />
 			<param index="0" name="x" type="float" />
@@ -107,6 +131,21 @@
 				[/codeblock]
 			</description>
 		</method>
+		<method name="atanh">
+			<return type="float" />
+			<param index="0" name="x" type="float" />
+			<description>
+				Returns the hyperbolic arc (also called inverse) tangent of [param x], returning a value in radians. Use it to get the angle from an angle's tangent in hyperbolic space if [param x] is between -1 and 1 (non-inclusive).
+				In mathematics, the inverse hyperbolic tangent is only defined for -1 &lt; [param x] &lt; 1 in the real set, so values equal or lower to -1 for [param x] return negative [constant @GDScript.INF] and values equal or higher than 1 return positive [constant @GDScript.INF] in order to prevent [method atanh] from returning [constant @GDScript.NAN].
+				[codeblock]
+				var a = atanh(0.9) # Returns 1.47221948958322
+				tanh(a) # Returns 0.9
+
+				var b = atanh(-2) # Returns -inf
+				tanh(b) # Returns -1
+				[/codeblock]
+			</description>
+		</method>
 		<method name="bezier_derivative">
 			<return type="float" />
 			<param index="0" name="start" type="float" />

diff --git a/tests/core/math/test_math_funcs.h b/tests/core/math/test_math_funcs.h
@@ -175,6 +175,37 @@ TEST_CASE_TEMPLATE("[Math] asin/acos/atan", T, float, double) {
 	CHECK(Math::atan((T)450.0) == doctest::Approx((T)1.5685741082));
 }
 
+TEST_CASE_TEMPLATE("[Math] asinh/acosh/atanh", T, float, double) {
+	CHECK(Math::asinh((T)-2.0) == doctest::Approx((T)-1.4436354751));
+	CHECK(Math::asinh((T)-0.1) == doctest::Approx((T)-0.0998340788));
+	CHECK(Math::asinh((T)0.1) == doctest::Approx((T)0.0998340788));
+	CHECK(Math::asinh((T)0.5) == doctest::Approx((T)0.4812118250));
+	CHECK(Math::asinh((T)1.0) == doctest::Approx((T)0.8813735870));
+	CHECK(Math::asinh((T)2.0) == doctest::Approx((T)1.4436354751));
+
+	CHECK(Math::acosh((T)-2.0) == doctest::Approx((T)0.0));
+	CHECK(Math::acosh((T)-0.1) == doctest::Approx((T)0.0));
+	CHECK(Math::acosh((T)0.1) == doctest::Approx((T)0.0));
+	CHECK(Math::acosh((T)0.5) == doctest::Approx((T)0.0));
+	CHECK(Math::acosh((T)1.0) == doctest::Approx((T)0.0));
+	CHECK(Math::acosh((T)2.0) == doctest::Approx((T)1.3169578969));
+	CHECK(Math::acosh((T)450.0) == doctest::Approx((T)6.8023935287));
+
+	CHECK(Math::is_inf(Math::atanh((T)-2.0)));
+	CHECK(Math::atanh((T)-2.0) < (T)0.0);
+	CHECK(Math::is_inf(Math::atanh((T)-1.0)));
+	CHECK(Math::atanh((T)-1.0) < (T)0.0);
+	CHECK(Math::atanh((T)-0.1) == doctest::Approx((T)-0.1003353477));
+	CHECK(Math::atanh((T)0.1) == doctest::Approx((T)0.1003353477));
+	CHECK(Math::atanh((T)0.5) == doctest::Approx((T)0.5493061443));
+	CHECK(Math::is_inf(Math::atanh((T)1.0)));
+	CHECK(Math::atanh((T)1.0) > (T)0.0);
+	CHECK(Math::is_inf(Math::atanh((T)1.5)));
+	CHECK(Math::atanh((T)1.5) > (T)0.0);
+	CHECK(Math::is_inf(Math::atanh((T)450.0)));
+	CHECK(Math::atanh((T)450.0) > (T)0.0);
+}
+
 TEST_CASE_TEMPLATE("[Math] sinc/sincn/atan2", T, float, double) {
 	CHECK(Math::sinc((T)-0.1) == doctest::Approx((T)0.9983341665));
 	CHECK(Math::sinc((T)0.1) == doctest::Approx((T)0.9983341665));