From 5d27461fa633f261a6af037bac9b8ce0953a25ba Mon Sep 17 00:00:00 2001
From: NetterSilver <133535268+Silvertree2010@users.noreply.github.com>
Date: Sun, 1 Nov 2026 02:55:58 +0100
Subject: [PATCH] Keep Xfrm::rot_norm within 0..360 for tiny negative rotations

Found while testing crates/geom/src/lib.rs:155-158

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 crates/geom/src/lib.rs | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/crates/geom/src/lib.rs b/crates/geom/src/lib.rs
index 3be72e03..6f695375 100644
--- a/crates/geom/src/lib.rs
+++ b/crates/geom/src/lib.rs
@@ -153,8 +153,8 @@ impl Xfrm {
     }
     /// Rotation normalised to 0..360.
     pub fn rot_norm(&self) -> f64 {
-        let r = self.rot % 360.0;
-        if r < 0.0 { r + 360.0 } else { r }
+        let r = self.rot.rem_euclid(360.0);
+        if r >= 360.0 { 0.0 } else { r }
     }
 }
 
@@ -266,6 +266,14 @@ mod tests {
         assert!((p.x - 300.0).abs() < 1e-9 && (p.y - 200.0).abs() < 1e-9);
     }
 
+    #[test]
+    fn rot_norm_stays_below_360() {
+        for rot in [-1e-15, -1e-13, -f64::EPSILON, -0.0, 360.0, 720.0, -360.0] {
+            let n = Xfrm { rot, ..Default::default() }.rot_norm();
+            assert!((0.0..360.0).contains(&n), "rot {rot} -> {n}");
+        }
+    }
+
     #[test]
     fn segment_distance() {
         assert!((dist_to_segment(Point::new(5.0, 5.0), Point::new(0.0, 0.0), Point::new(10.0, 0.0)) - 5.0).abs() < 1e-9);