From 7717d69561a5495ea5ca9f5760847535ef13a904 Mon Sep 17 00:00:00 2001
From: Pascal Martin <pascal.fb.martin@gmail.com>
Date: Sun, 8 Jan 2023 11:11:53 -0800
Subject: [PATCH] tv_usec must always be positive

---
 hc_clock.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hc_clock.c b/hc_clock.c
index e11ee51..94ab4ab 100644
--- a/hc_clock.c
+++ b/hc_clock.c
@@ -185,6 +185,12 @@ static void hc_clock_adjust (time_t drift) {
 
     delta.tv_sec = (drift / 1000);
     delta.tv_usec = (drift % 1000) * 1000;
+    if (delta.tv_usec < 0) {
+        // Per the GNU libc documentation, tv_usec must be positive, and
+        // microsecond time = (tv_sec * 1000000) + tv_usec.
+        delta.tv_sec -= 1;
+        delta.tv_usec += 1000000;
+    }
     if (adjtime (&delta, NULL) != 0) {
         printf ("adjtime() error %d\n", errno);
     }