From 0172082262f2f7185c3159dd3d1a6cf5f17358bd Mon Sep 17 00:00:00 2001
From: Reece Stevens <reecestevens24@gmail.com>
Date: Tue, 19 Jun 2018 23:21:14 -0500
Subject: [PATCH] Fix len miscalculation when head > tail

---
 src/ring_buffer/mod.rs |  2 +-
 tests/tsan.rs          | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/ring_buffer/mod.rs b/src/ring_buffer/mod.rs
index 807283da..be7a35cf 100644
--- a/src/ring_buffer/mod.rs
+++ b/src/ring_buffer/mod.rs
@@ -335,7 +335,7 @@ macro_rules! impl_ {
                 let tail = self.tail.load_relaxed();
 
                 if head > tail {
-                    head - tail
+                    self.capacity() + 1 - head + tail
                 } else {
                     tail - head
                 }
diff --git a/tests/tsan.rs b/tests/tsan.rs
index fe9a36d9..8168399c 100644
--- a/tests/tsan.rs
+++ b/tests/tsan.rs
@@ -155,3 +155,20 @@ fn unchecked() {
 
     assert_eq!(rb.len(), N::to_usize() / 2);
 }
+
+#[test]
+fn len_properly_wraps() {
+    type N = U3;
+    let mut rb: RingBuffer<u8, N> = RingBuffer::new();
+
+    rb.enqueue(1).unwrap();
+    assert_eq!(rb.len(), 1);
+    rb.dequeue();
+    assert_eq!(rb.len(), 0);
+    rb.enqueue(2).unwrap();
+    assert_eq!(rb.len(), 1);
+    rb.enqueue(3).unwrap();
+    assert_eq!(rb.len(), 2);
+    rb.enqueue(4).unwrap();
+    assert_eq!(rb.len(), 3);
+}