From 38e39b7086bbd5747dc61a84faf54ec9a58fa535 Mon Sep 17 00:00:00 2001
From: Kris Nuttycombe <kris@nutty.land>
Date: Fri, 15 Mar 2024 09:17:12 -0600
Subject: [PATCH] Implement `{PartialOrd, Ord, Hash}` for `DiversifierIndex`

---
 CHANGELOG.md |  3 +++
 src/lib.rs   | 30 +++++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 43a4030..63af005 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,9 @@ and this library adheres to Rust's notion of
 
 ## [Unreleased]
 
+### Added
+- `impl {PartialOrd, Ord, Hash}` for `zip32::DiversifierIndex`
+
 ## [0.1.1] - 2024-03-14
 
 ### Added
diff --git a/src/lib.rs b/src/lib.rs
index 68aed68..f0122c4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -149,7 +149,7 @@ impl ChainCode {
 }
 
 /// The index for a particular diversifier.
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct DiversifierIndex([u8; 11]);
 
 impl Default for DiversifierIndex {
@@ -214,6 +214,26 @@ impl From<DiversifierIndex> for u128 {
     }
 }
 
+impl PartialOrd for DiversifierIndex {
+    fn partial_cmp(&self, other: &Self) -> Option<core::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for DiversifierIndex {
+    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
+        self.0
+            .iter()
+            .rev()
+            .zip(other.0.iter().rev())
+            .find_map(|(a, b)| match a.cmp(b) {
+                core::cmp::Ordering::Equal => None,
+                ineq => Some(ineq),
+            })
+            .unwrap_or(core::cmp::Ordering::Equal)
+    }
+}
+
 impl DiversifierIndex {
     /// Constructs the zero index.
     pub fn new() -> Self {
@@ -375,4 +395,12 @@ mod tests {
 
         assert_matches!(di.increment(), Err(_));
     }
+
+    #[test]
+    fn diversifier_index_ord() {
+        assert!(DiversifierIndex::from(1u64) < DiversifierIndex::from(2u64));
+        assert!(DiversifierIndex::from(u64::MAX - 1) < DiversifierIndex::from(u64::MAX));
+        assert!(DiversifierIndex::from(3u64) == DiversifierIndex::from(3u64));
+        assert!(DiversifierIndex::from(u64::MAX) == DiversifierIndex::from(u64::MAX));
+    }
 }