From 583c0f8ce60ad16d5bc8e46211d14aa6e5b345c2 Mon Sep 17 00:00:00 2001
From: Anders Olsson <anders.e.olsson@gmail.com>
Date: Sat, 13 Oct 2018 11:40:03 +0200
Subject: [PATCH] Initial commit.

---
 .gitignore |  3 +++
 Cargo.toml |  6 ++++++
 src/lib.rs | 27 +++++++++++++++++++++++++++
 3 files changed, 36 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.toml
 create mode 100644 src/lib.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6936990
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+/target
+**/*.rs.bk
+Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..9213efd
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "elo"
+version = "0.1.0"
+authors = ["Anders Olsson <anders.e.olsson@gmail.com>"]
+
+[dependencies]
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..5538659
--- /dev/null
+++ b/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);
+    }
+}