1 files changed, 89 insertions, 0 deletions
diff --git a/src/pitch.rs b/src/pitch.rs
new file mode 100644
index 0000000..0944bbf
--- /dev/null
+++ b/src/pitch.rs
@@ -0,0 +1,89 @@
+use std::fmt;
+use std::f32;
+
+#[derive(Debug, Clone, Copy)]
+pub struct Pitch {
+    pub hz: f32
+}
+
+impl Pitch {
+    pub fn new(hz: f32) -> Pitch {
+        Pitch {
+            hz: hz
+        }
+    }
+    
+    fn midi_number(&self) -> f32 {
+        69.0 + 12.0 * (self.hz / 440.0).log2()
+    }
+
+    pub fn cents_error(&self) -> f32 {
+        if !self.hz.is_finite() {
+            return f32::NAN;
+        }
+        
+        let midi_number = self.midi_number();
+        let cents = (midi_number - midi_number.floor()) * 100.0;
+        if cents >= 50.0 {
+            cents - 100.0
+        }
+        else {
+            cents
+        }
+    }
+}
+
+impl fmt::Display for Pitch {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.hz <= 0.0 || !self.hz.is_finite() {
+            write!(f, "")
+        } else {
+            let pitch_names = [
+                "C",
+                "C♯",
+                "D",
+                "E♭",
+                "E",
+                "F",
+                "F♯",
+                "G",
+                "G♯",
+                "A",
+                "B♭",
+                "B"
+            ];
+
+            //midi_number of 0 is C-1.
+            let rounded_pitch = self.midi_number().round() as i32;
+            let name = pitch_names[rounded_pitch as usize % pitch_names.len()];
+            let octave = rounded_pitch / pitch_names.len() as i32 - 1;
+
+            write!(f, "{: <2}{}", name, octave)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    
+    #[test]
+    fn a4_is_correct() {
+        assert_eq!(format!("{}", Pitch::new(440.0)), "A 4");
+    }
+
+    #[test]
+    fn a2_is_correct() {
+        assert_eq!(format!("{}", Pitch::new(110.0)), "A 2");
+    }
+
+    #[test]
+    fn c4_is_correct() {
+        assert_eq!(format!("{}", Pitch::new(261.63)), "C 4");
+    }
+
+    #[test]
+    fn f5_is_correct() {
+        assert_eq!(format!("{}", Pitch::new(698.46)), "F 5");
+    }
+}