3 files changed, 44 insertions, 12 deletions

diff --git a/src/lib.rs b/src/lib.rs
index cd3320a..c41b791 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,19 @@
 pub mod volume;
 
 type Percent = u8;
+
+pub fn round<F, I>(f: F, digits: I) -> f64
+where
+    F: Into<f64>,
+    I: Into<i32> + Copy,
+{
+    (f.into() * 10_f64.powi(digits.into())).round() / 10_f64.powi(digits.into())
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn round() {
+        assert_eq!(super::round(0.123456789, 3), 0.123);
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 4c6cf43..aabef0a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,7 +3,12 @@ use iced::{
     Element, Sandbox, Settings,
 };
 
-use volute::volume::{self, CubicMetre};
+use volute::{
+    round,
+    volume::{self, CubicMetre},
+};
+
+const DECIMAL_DIGITS: i8 = 4;
 
 pub fn main() -> iced::Result {
     App::run(Settings::default())
@@ -33,6 +38,25 @@ impl App {
     }
 }
 
+impl UI {
+    fn convert_displacement(&mut self, unit: volume::Unit) {
+        if self.displacement.len() > 0 {
+            self.displacement = format!(
+                "{}",
+                round(
+                    volume::convert(
+                        self.displacement.parse::<f64>().unwrap(),
+                        self.displacement_unit,
+                        unit,
+                    ),
+                    DECIMAL_DIGITS,
+                ),
+            );
+        }
+        self.displacement_unit = unit;
+    }
+}
+
 impl Sandbox for App {
     type Message = Message;
 
@@ -50,15 +74,7 @@ impl Sandbox for App {
                 self.set_displacement(&displacement);
             }
             Message::DisplacementUnit(unit) => {
-                self.ui.displacement = format!(
-                    "{:.2}",
-                    volume::convert(
-                        self.ui.displacement.parse::<f64>().unwrap(),
-                        self.ui.displacement_unit,
-                        unit,
-                    )
-                );
-                self.ui.displacement_unit = unit;
+                self.ui.convert_displacement(unit);
             }
         }
     }
diff --git a/src/volume.rs b/src/volume.rs
index 933ae49..5818ea4 100644
--- a/src/volume.rs
+++ b/src/volume.rs
@@ -41,7 +41,7 @@ impl CubicMetre {
 
 impl From<Litre> for CubicMetre {
     fn from(value: Litre) -> Self {
-        Self(value.0 * 10_f64.powf(-3.))
+        Self(value.0 * 10_f64.powi(-3))
     }
 }
 
@@ -56,7 +56,7 @@ impl<F: Into<f64>> From<F> for Litre {
 
 impl From<CubicMetre> for Litre {
     fn from(value: CubicMetre) -> Self {
-        Self(value.0 * 10_f64.powf(3.))
+        Self(value.0 * 10_f64.powi(3))
     }
 }