From 5d547130f05dc1410cfc2707f213fd216c3920db Mon Sep 17 00:00:00 2001
From: "mergify[bot]" <37929162+mergify[bot]@users.noreply.github.com>
Date: Mon, 20 Apr 2020 01:25:41 -0700
Subject: [PATCH] Calculate distance between u64 without overflow (#9592)
 (#9599)

automerge
---
 core/src/broadcast_stage.rs | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/core/src/broadcast_stage.rs b/core/src/broadcast_stage.rs
index 46095c2150..bd841db703 100644
--- a/core/src/broadcast_stage.rs
+++ b/core/src/broadcast_stage.rs
@@ -412,11 +412,19 @@ pub fn broadcast_shreds(
     Ok(())
 }
 
+fn distance(a: u64, b: u64) -> u64 {
+    if a > b {
+        a - b
+    } else {
+        b - a
+    }
+}
+
 fn num_live_peers(peers: &[ContactInfo]) -> i64 {
     let mut num_live_peers = 1i64;
     peers.iter().for_each(|p| {
         // A peer is considered live if they generated their contact info recently
-        if timestamp() - p.wallclock <= CRDS_GOSSIP_PULL_CRDS_TIMEOUT_MS {
+        if distance(timestamp(), p.wallclock) <= CRDS_GOSSIP_PULL_CRDS_TIMEOUT_MS {
             num_live_peers += 1;
         }
     });
@@ -506,6 +514,17 @@ pub mod test {
         assert_eq!(num_expected_coding_shreds, coding_index);
     }
 
+    #[test]
+    fn test_num_live_peers() {
+        let mut ci = ContactInfo::default();
+        ci.wallclock = std::u64::MAX;
+        assert_eq!(num_live_peers(&[ci.clone()]), 1);
+        ci.wallclock = timestamp() - 1;
+        assert_eq!(num_live_peers(&[ci.clone()]), 2);
+        ci.wallclock = timestamp() - CRDS_GOSSIP_PULL_CRDS_TIMEOUT_MS - 1;
+        assert_eq!(num_live_peers(&[ci]), 1);
+    }
+
     #[test]
     fn test_duplicate_retransmit_signal() {
         // Setup