From b62908d4260d1e3a9806a70e37aead2ea803a912 Mon Sep 17 00:00:00 2001
From: Adam Reichold <adam.reichold@t-online.de>
Date: Tue, 5 May 2020 15:12:25 +0200
Subject: [PATCH] Implement inverse trigonometric functions from ratio to
 angle.

---
 src/si/angle.rs | 25 ++++++++++++++
 src/si/ratio.rs | 89 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 114 insertions(+)

diff --git a/src/si/angle.rs b/src/si/angle.rs
index a7b4d87c..13857507 100644
--- a/src/si/angle.rs
+++ b/src/si/angle.rs
@@ -76,6 +76,22 @@ where
     }
 }
 
+#[cfg(feature = "std")]
+impl<D, U, V> ::si::Quantity<D, U, V>
+where
+    D: ::si::Dimension + ?Sized,
+    U: ::si::Units<V> + ?Sized,
+    V: ::num::Float + ::Conversion<V>,
+    radian: ::Conversion<V, T = V::T>,
+{
+    /// Computes the four quadrant arctangent of self (y) and other (x).
+    #[inline(always)]
+    pub fn atan2(self, other: Self) -> Angle<U, V>
+    {
+        Angle::new::<radian>(self.value.atan2(other.value))
+    }
+}
+
 mod convert {
     use super::*;
 
@@ -148,6 +164,7 @@ mod tests {
             use ::lib::f64::consts::PI;
             use num::{FromPrimitive, Zero};
             use si::angle as a;
+            use si::length as l;
             use si::quantities::*;
             use tests::Test;
 
@@ -190,6 +207,14 @@ mod tests {
                 Test::assert_approx_eq(&zero.tanh(), &0.0);
                 Test::assert_approx_eq(&nzero.tanh(), &0.0);
             }
+
+            quickcheck! {
+                #[allow(trivial_casts)]
+                fn atan2(y: V, x: V) -> bool {
+                    Test::eq(&y.atan2(x),
+                        &Length::new::<l::meter>(y).atan2(Length::new::<l::meter>(x)).get::<a::radian>())
+                }
+            }
         }
     }
 }
diff --git a/src/si/ratio.rs b/src/si/ratio.rs
index bd0d4942..4a3f853b 100644
--- a/src/si/ratio.rs
+++ b/src/si/ratio.rs
@@ -1,5 +1,8 @@
 //! Ratio (dimensionless quantity).
 
+#[cfg(feature = "std")]
+use super::angle::{Angle, radian};
+
 quantity! {
     /// Ratio (dimensionless quantity).
     quantity: Ratio; "ratio";
@@ -29,6 +32,51 @@ quantity! {
     }
 }
 
+/// Implementation of various stdlib inverse trigonometric functions
+#[cfg(feature = "std")]
+impl<U, V> Ratio<U, V>
+where
+    U: ::si::Units<V> + ?Sized,
+    V: ::num::Float + ::Conversion<V>,
+    radian: ::Conversion<V, T = V::T>,
+{
+    /// Computes the value of the inverse cosine of the ratio.
+    #[inline(always)]
+    pub fn acos(self) -> Angle<U, V> {
+        Angle::new::<radian>(self.value.acos())
+    }
+
+    /// Computes the value of the inverse hyperbolic cosine of the ratio.
+    #[inline(always)]
+    pub fn acosh(self) -> Angle<U, V> {
+        Angle::new::<radian>(self.value.acosh())
+    }
+
+    /// Computes the value of the inverse sine of the ratio.
+    #[inline(always)]
+    pub fn asin(self) -> Angle<U, V> {
+        Angle::new::<radian>(self.value.asin())
+    }
+
+    /// Computes the value of the inverse hyperbolic sine of the ratio.
+    #[inline(always)]
+    pub fn asinh(self) -> Angle<U, V> {
+        Angle::new::<radian>(self.value.asinh())
+    }
+
+    /// Computes the value of the inverse tangent of the ratio.
+    #[inline(always)]
+    pub fn atan(self) -> Angle<U, V> {
+        Angle::new::<radian>(self.value.atan())
+    }
+
+    /// Computes the value of the inverse hyperbolic tangent of the ratio.
+    #[inline(always)]
+    pub fn atanh(self) -> Angle<U, V> {
+        Angle::new::<radian>(self.value.atanh())
+    }
+}
+
 mod convert {
     use super::*;
 
@@ -103,4 +151,45 @@ mod tests {
                 &Ratio::new::<r::part_per_quadrillion>(V::one()));
         }
     }
+
+    #[cfg(feature = "std")]
+    mod inv_trig {
+        storage_types! {
+            types: Float;
+
+            use si::angle as a;
+            use si::quantities::*;
+            use tests::Test;
+
+            fn test_nan_or_eq(yl: V, yr: V) -> bool {
+                (yl.is_nan() && yr.is_nan()) || Test::eq(&yl, &yr)
+            }
+
+            quickcheck! {
+                fn acos(x: V) -> bool {
+                    test_nan_or_eq(x.acos(), Ratio::from(x).acos().get::<a::radian>())
+                }
+
+                fn acosh(x: V) -> bool {
+                    test_nan_or_eq(x.acosh(), Ratio::from(x).acosh().get::<a::radian>())
+                }
+
+                fn asin(x: V) -> bool {
+                    test_nan_or_eq(x.asin(), Ratio::from(x).asin().get::<a::radian>())
+                }
+
+                fn asinh(x: V) -> bool {
+                    test_nan_or_eq(x.asinh(), Ratio::from(x).asinh().get::<a::radian>())
+                }
+
+                fn atan(x: V) -> bool {
+                    test_nan_or_eq(x.atan(), Ratio::from(x).atan().get::<a::radian>())
+                }
+
+                fn atanh(x: V) -> bool {
+                    test_nan_or_eq(x.atanh(), Ratio::from(x).atanh().get::<a::radian>())
+                }
+            }
+        }
+    }
 }