From 52d317c8ffff9fcac9b2a48e6353aa3b87cb4518 Mon Sep 17 00:00:00 2001
From: Harrison Booth <73434116+Harrison-Booth@users.noreply.github.com>
Date: Fri, 30 Oct 2026 19:23:51 -0500
Subject: [PATCH] Validate places for negative base conversions

---
 crates/functions/src/engineering.rs | 28 ++++++++++++++++++++++------
 docs/function-parity.md             |  4 +++-
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/crates/functions/src/engineering.rs b/crates/functions/src/engineering.rs
index dbe6734d3..d00966671 100644
--- a/crates/functions/src/engineering.rs
+++ b/crates/functions/src/engineering.rs
@@ -62,6 +62,15 @@ fn format_base(v: i64, radix: u32, places: Option<f64>) -> R<Value> {
     if v < min || v > max {
         return Err(CellError::Num);
     }
+    let places = places
+        .map(|p| {
+            let p = p.trunc();
+            if !(1.0..=10.0).contains(&p) {
+                return Err(CellError::Num);
+            }
+            Ok(p as usize)
+        })
+        .transpose()?;
     if v < 0 {
         let u = v + (1i64 << bits);
         return text_val(to_radix(u, radix));
@@ -70,11 +79,6 @@ fn format_base(v: i64, radix: u32, places: Option<f64>) -> R<Value> {
     match places {
         None => text_val(s),
         Some(p) => {
-            let p = p.trunc();
-            if !(1.0..=10.0).contains(&p) {
-                return Err(CellError::Num);
-            }
-            let p = p as usize;
             if s.len() > p {
                 return Err(CellError::Num);
             }
@@ -97,7 +101,13 @@ fn to_radix(mut v: i64, radix: u32) -> String {
 }
 
 fn places_arg(a: &[Arg]) -> R<Option<f64>> {
-    if has(a, 1) { Ok(Some(num(a, 1)?)) } else { Ok(None) }
+    if !has(a, 1) {
+        return Ok(None);
+    }
+    if matches!(a.get(1).map(scalar), Some(Value::Bool(_))) {
+        return Err(CellError::Value);
+    }
+    Ok(Some(num(a, 1)?))
 }
 
 fn convert_base(a: &[Arg], from: u32, to: u32) -> R<Value> {
@@ -402,6 +412,12 @@ mod tests {
         is_text(ev("BIN2OCT", vec![n(1111111111.0)]), "7777777777");
         is_text(ev("DEC2BIN", vec![n(9.0), n(4.0)]), "1001");
         is_text(ev("DEC2BIN", vec![n(-100.0)]), "1110011100");
+        is_err(ev("DEC2BIN", vec![n(-1.0), n(0.0)]), CellError::Num);
+        is_err(ev("DEC2HEX", vec![n(-1.0), n(11.0)]), CellError::Num);
+        is_err(ev("DEC2OCT", vec![n(-1.0), n(-1.0)]), CellError::Num);
+        is_err(ev("DEC2BIN", vec![n(1.0), crate::Arg::val(Value::Bool(true))]), CellError::Value);
+        is_text(ev("DEC2BIN", vec![n(-1.0), n(1.0)]), "1111111111");
+        is_text(ev("DEC2HEX", vec![n(-1.0), n(10.0)]), "FFFFFFFFFF");
         is_err(ev("DEC2BIN", vec![n(512.0)]), CellError::Num);
         is_text(ev("DEC2HEX", vec![n(100.0), n(4.0)]), "0064");
         is_text(ev("DEC2HEX", vec![n(-54.0)]), "FFFFFFFFCA");
diff --git a/docs/function-parity.md b/docs/function-parity.md
index d9823e8bf..e23a196fa 100644
--- a/docs/function-parity.md
+++ b/docs/function-parity.md
@@ -1,6 +1,6 @@
 # Function parity: worksheet functions and formulas
 
-> **Last reviewed:** 2026-10-15 · **Last updated:** 2026-10-27 · **Change:** minor (ECMA.CEILING listed with USDOLLAR as not on Microsoft's list; earlier: IMSQRT reproduces the stray real part Excel gives for negative reals, and the other IM* differences from Excel are listed; earlier: the LAMBDA row lists the recursion limit and its `#NUM!`, and the error a defined name holding an error gives when called; earlier: number text with accounting parentheses coerces like Excel 365; INDEX with one index on a 2-D reference is #REF! as in Excel; earlier: SUBTOTAL and AGGREGATE cap the cells they visit, #2175) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (base-conversion places are validated for negative inputs and reject Boolean arguments, as observed in Excel; earlier: ECMA.CEILING listed with USDOLLAR as not on Microsoft's list; IMSQRT reproduces Excel's stray real part for negative reals) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
 
 Excel's worksheet functions, category by category, against GridCraft's function library. Part of
 [target-app-parity.md](target-app-parity.md); gaps feed [gaps.md](gaps.md).
@@ -29,6 +29,8 @@ Excel's worksheet functions, category by category, against GridCraft's function
 
 ## Coverage
 
+| 2026-10-31 | minor | DEC2BIN, DEC2HEX and DEC2OCT validate `places` before returning negative two's-complement output, and Boolean places return `#VALUE!`, matching Excel |
+
 **Measured: 513 / 523 by name (98.1%); 504 / 523 working (96.4%).**
 
 | Category | Excel | Ours | Working | % working | Missing |