From dc5486ba8801625069fc6172b03e897612f42a90 Mon Sep 17 00:00:00 2001
From: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date: Tue, 24 Jan 2017 01:56:00 +0100
Subject: Fix bissextile years computation

In practice, fixes 2100, 2200, 2300, 2500, 2600, 2700, etc.

* i386/i386at/rtc.c (yeartoday): Make years divisible by 100 but not
divisible by 400 non-bisextile.
---
 i386/i386at/rtc.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/i386/i386at/rtc.c b/i386/i386at/rtc.c
index 01e09772..b284c332 100644
--- a/i386/i386at/rtc.c
+++ b/i386/i386at/rtc.c
@@ -109,7 +109,24 @@ static int month[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
 int
 yeartoday(int year)
 {
-	return((year%4) ? 365 : 366);
+	if (year%4)
+		/* Not divisible by 4, not bissextile */
+		return 365;
+
+	/* Divisible by 4 */
+	if (year % 100)
+		/* Not divisible by 100, bissextile */
+		return 366;
+
+	/* Divisible by 100 */
+	if (year % 400)
+		/* Not divisible by 400, not bissextile */
+		return 365;
+
+	/* Divisible by 400 */
+	/* Rules for 2000 and further have not been officially decided yet.
+	 * 2000 was made bissextile.  */
+	return 366;
 }
 
 int
-- 
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