Initial commit.

src/lib.rs

@@ -0,0 +1,27 @@
+pub fn rating(a: f32, b: f32, score: f32, n: f32, k: f32) -> f32 {
+    a + delta(score, expected(a, b, n), k)
+}
+
+fn delta(score: f32, rating: f32, k: f32) -> f32 {
+    k * (score - rating)
+}
+
+fn expected(a: f32, b: f32, n: f32) -> f32 {
+    1.0 / (1.0 + 10.0_f32.powf((b - a) / n))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_rating() {
+        let r = rating(1600.0, 1600.0, 1.0, 400.0, 32.0);
+
+        assert_eq!(r, 1616.0);
+
+        let r = rating(1600.0, 1600.0, 0.5, 400.0, 32.0);
+
+        assert_eq!(r, 1600.0);
+    }
+}