From cacde79ed6c866a370dd58f97ed1baa31b0b2c35 Mon Sep 17 00:00:00 2001
From: Meghan Denny <hello@nektro.net>
Date: Tue, 1 Sep 2026 13:38:42 -0700
Subject: [PATCH] optimize isLeapYear

---
 time.zig | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/time.zig b/time.zig
index bd012d59a30e48b89db7f718499627f7fa91daaf..c0e605d2646e065a7b832b899f05d152dc2daf27 100644
--- a/time.zig
+++ b/time.zig
@@ -509,12 +509,12 @@ pub const Era = enum {
     }
 };
 
+// https://hueffner.de/falk/blog/a-leap-year-check-in-three-instructions.html
 pub fn isLeapYear(year: u16) bool {
-    var ret = false;
-    if (year % 4 == 0) ret = true;
-    if (year % 100 == 0) ret = false;
-    if (year % 400 == 0) ret = true;
-    return ret;
+    if (year % 4 != 0) return false;
+    if (year % 25 != 0) return true;
+    if (year % 16 == 0) return true;
+    return false;
 }
 
 pub fn daysInYear(year: u16) u16 {
-- 
2.54.0