OrderedFloat refactor (#918)

* Move egui/util/float_ord.rs -> epaint/util/ordered_float.rs

* Implement Hash on OrderedFloat

* Generic OrderedFloat<T>; impl Hash; documentation

egui/src/util/mod.rs

@@ -2,7 +2,6 @@
 
 pub mod cache;
 pub(crate) mod fixed_cache;
-pub(crate) mod float_ord;
 mod history;
 pub mod id_type_map;
 pub mod undoer;

egui/src/widgets/plot/items/mod.rs

@@ -2,9 +2,9 @@
 
 use std::ops::RangeInclusive;
 
+use epaint::util::FloatOrd;
 use epaint::Mesh;
 
-use crate::util::float_ord::FloatOrd;
 use crate::*;
 
 use super::{PlotBounds, ScreenTransform};

egui/src/widgets/plot/mod.rs

@@ -1,9 +1,9 @@
 //! Simple plotting library.
 
-use crate::util::float_ord::FloatOrd;
 use crate::*;
-use color::Hsva;
 use epaint::ahash::AHashSet;
+use epaint::color::Hsva;
+use epaint::util::FloatOrd;
 use items::PlotItem;
 use legend::LegendWidget;
 use transform::{PlotBounds, ScreenTransform};

epaint/src/lib.rs

@@ -196,3 +196,15 @@ pub(crate) fn f32_hash<H: std::hash::Hasher>(state: &mut H, f: f32) {
         f.to_bits().hash(state);
     }
 }
+
+#[inline(always)]
+pub(crate) fn f64_hash<H: std::hash::Hasher>(state: &mut H, f: f64) {
+    if f == 0.0 {
+        state.write_u8(0);
+    } else if f.is_nan() {
+        state.write_u8(1);
+    } else {
+        use std::hash::Hash;
+        f.to_bits().hash(state);
+    }
+}

epaint/src/util.rs → epaint/src/util/mod.rs

@@ -1,3 +1,7 @@
+mod ordered_float;
+
+pub use ordered_float::*;
+
 /// Hash the given value with a predictable hasher.
 #[inline]
 pub fn hash(value: impl std::hash::Hash) -> u64 {

epaint/src/util/ordered_float.rs

@@ -0,0 +1,127 @@
+//! Total order on floating point types.
+//! Can be used for sorting, min/max computation, and other collection algorithms.
+
+use std::cmp::Ordering;
+use std::hash::{Hash, Hasher};
+
+/// Wraps a floating-point value to add total order and hash.
+/// Possible types for `T` are `f32` and `f64`.
+///
+/// See also [`FloatOrd`].
+pub struct OrderedFloat<T>(T);
+
+impl<T: Float> Eq for OrderedFloat<T> {}
+
+impl<T: Float> PartialEq<Self> for OrderedFloat<T> {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        // NaNs are considered equal (equivalent) when it comes to ordering
+        if self.0.is_nan() {
+            other.0.is_nan()
+        } else {
+            self.0 == other.0
+        }
+    }
+}
+
+impl<T: Float> PartialOrd<Self> for OrderedFloat<T> {
+    #[inline]
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        match self.0.partial_cmp(&other.0) {
+            Some(ord) => Some(ord),
+            None => Some(self.0.is_nan().cmp(&other.0.is_nan())),
+        }
+    }
+}
+
+impl<T: Float> Ord for OrderedFloat<T> {
+    #[inline]
+    fn cmp(&self, other: &Self) -> Ordering {
+        match self.partial_cmp(other) {
+            Some(ord) => ord,
+            None => unreachable!(),
+        }
+    }
+}
+
+impl<T: Float> Hash for OrderedFloat<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.0.hash(state);
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+/// Extension trait to provide `ord()` method.
+///
+/// Example with `f64`:
+/// ```
+/// use epaint::util::FloatOrd;
+///
+/// let array = [1.0, 2.5, 2.0];
+/// let max = array.iter().max_by_key(|val| val.ord());
+///
+/// assert_eq!(max, Some(&2.5));
+/// ```
+pub trait FloatOrd {
+    /// Type to provide total order, useful as key in sorted contexts.
+    fn ord(self) -> OrderedFloat<Self>
+    where
+        Self: Sized;
+}
+
+impl FloatOrd for f32 {
+    #[inline]
+    fn ord(self) -> OrderedFloat<f32> {
+        OrderedFloat(self)
+    }
+}
+
+impl FloatOrd for f64 {
+    #[inline]
+    fn ord(self) -> OrderedFloat<f64> {
+        OrderedFloat(self)
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+/// Internal abstraction over floating point types
+#[doc(hidden)]
+pub trait Float: PartialOrd + PartialEq + private::FloatImpl {}
+impl Float for f32 {}
+impl Float for f64 {}
+
+// Keep this trait in private module, to avoid exposing its methods as extensions in user code
+mod private {
+    use super::*;
+
+    pub trait FloatImpl {
+        fn is_nan(&self) -> bool;
+        fn hash<H: Hasher>(&self, state: &mut H);
+    }
+
+    impl FloatImpl for f32 {
+        #[inline]
+        fn is_nan(&self) -> bool {
+            f32::is_nan(*self)
+        }
+
+        #[inline]
+        fn hash<H: Hasher>(&self, state: &mut H) {
+            crate::f32_hash(state, *self);
+        }
+    }
+
+    impl FloatImpl for f64 {
+        #[inline]
+        fn is_nan(&self) -> bool {
+            f64::is_nan(*self)
+        }
+
+        #[inline]
+        fn hash<H: Hasher>(&self, state: &mut H) {
+            crate::f64_hash(state, *self);
+        }
+    }
+}