From 67fce0f63c13974a9f1d73e9cafa3e208bacc8ef Mon Sep 17 00:00:00 2001
From: Nigel Ihza Firdausy <106657905+Ni-zav@users.noreply.github.com>
Date: Sat, 10 Oct 2026 15:54:14 +0700
Subject: [PATCH] fix(geom): carry rounded pica and cicero fractions

Apply the displayed precision before testing for a 12-point carry,
so measurements near a pica/cicero boundary do not display as 0p12
or 0c12. Cover positive, negative, coarse, and subunit rounding.
---
 crates/geom/src/units.rs | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/crates/geom/src/units.rs b/crates/geom/src/units.rs
index 7b5aae77..0e0c9b4b 100644
--- a/crates/geom/src/units.rs
+++ b/crates/geom/src/units.rs
@@ -270,7 +270,12 @@ pub fn format_measure_prec(pt: f64, unit: Unit, decimals: usize) -> String {
             let a = pt.abs();
             let mut whole = (a / big).floor();
             let mut rest = (a - whole * big) / small;
-            if (rest - 12.0).abs() < 1e-6 || rest > 12.0 - 1e-6 {
+            // Carry when the displayed fractional points round up to a full pica/cicero.
+            // Checking unrounded rest misses values such as 11.9999 at 3 decimals,
+            // which would otherwise render as the misleading "0p12".
+            let scale = 10.0_f64.powi(decimals.min(12) as i32);
+            rest = (rest * scale).round() / scale;
+            if rest >= 12.0 {
                 whole += 1.0;
                 rest = 0.0;
             }
@@ -335,6 +340,17 @@ mod tests {
         assert!(parse_measure("50%", Unit::Points).is_err());
     }
 
+    #[test]
+    fn pica_and_cicero_rounding_carries_into_the_major_unit() {
+        assert_eq!(format_measure_prec(11.9999, Unit::Picas, 3), "1p0");
+        assert_eq!(format_measure_prec(-11.9999, Unit::Picas, 3), "-1p0");
+        assert_eq!(format_measure_prec(11.9994, Unit::Picas, 3), "0p11.999");
+        assert_eq!(format_measure_prec(11.6, Unit::Picas, 0), "1p0");
+        let almost_cicero = PT_PER_CICERO - 0.0001 * PT_PER_DIDOT;
+        assert_eq!(format_measure_prec(almost_cicero, Unit::Ciceros, 3), "1c0");
+        assert!(close(p(&format_measure_prec(11.9999, Unit::Picas, 3)), 12.0));
+    }
+
     #[test]
     fn formatting() {
         assert_eq!(format_measure(18.0, Unit::Picas), "1p6");