From 2c2d92ef6b595aed9a03326474a0fcc7b008dd79 Mon Sep 17 00:00:00 2001
From: MarekSpodBiedry <73122968+MarekSpodBiedry@users.noreply.github.com>
Date: Fri, 9 Oct 2026 19:29:29 +0200
Subject: [PATCH] ROUND: keep 15 significant digits when asked for 15+ digits,
 so ROUND(0.1+0.2,15) is 0.3 (#58)

---
 crates/functions/src/util.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/crates/functions/src/util.rs b/crates/functions/src/util.rs
index fca5dc4..5296c48 100644
--- a/crates/functions/src/util.rs
+++ b/crates/functions/src/util.rs
@@ -235,7 +235,9 @@ pub(crate) fn round_half_away(x: f64, digits: i32) -> f64 {
     // value = 0.d1d2…d15 × 10^(e+1); keep the first `keep` digits.
     let keep = e + 1 + digits;
     if keep >= d.len() as i64 {
-        return x;
+        // Nothing to round off, but Excel still keeps only 15 significant digits, which drops binary noise
+        // such as 0.1 + 0.2 = 0.30000000000000004.
+        return to_sig_digits(x, d.len());
     }
     if keep < 0 {
         return 0.0;
@@ -416,6 +418,8 @@ mod tests {
         assert_eq!(round_half_away(1234.5678, -2), 1200.0);
         assert_eq!(round_half_away(0.285, 2), 0.29);
         assert_eq!(round_half_away(1.005, 2), 1.01);
+        assert_eq!(round_half_away(0.1 + 0.2, 15), 0.3);
+        assert_eq!(round_half_away(0.1 + 0.2, 20), 0.3);
     }
 
     #[test]