Merge PR #2991

# Conflicts:
#	docs/function-parity.md

crates/functions/src/engineering.rs

@@ -185,6 +185,9 @@ fn bitxor(a: &[Arg], _c: &mut dyn Ctx) -> R<Value> {
 fn shift(a: &[Arg], left: bool) -> R<Value> {
     let n = bit_operand(a, 0)?;
     let s = num(a, 1)?.trunc();
+    if n == 0 {
+        return Ok(Value::Number(0.0));
+    }
     if s.abs() > 53.0 {
         return Err(CellError::Num);
     }
@@ -477,6 +480,21 @@ mod tests {
         is_err(ev("BITAND", vec![n(1.5), n(5.0)]), CellError::Num);
         is_err(ev("BITLSHIFT", vec![n(1.0), n(54.0)]), CellError::Num);
         is_err(ev("BITLSHIFT", vec![n(2f64.powi(47)), n(1.0)]), CellError::Num);
+        for f in ["BITLSHIFT", "BITRSHIFT"] {
+            for shift in [-100.0, -54.0, -53.0, 53.0, 54.0, 100.0] {
+                close(ev(f, vec![n(0.0), n(shift)]), 0.0);
+            }
+            for shift in [-100.0, -54.0, 54.0, 100.0] {
+                is_err(ev(f, vec![n(1.0), n(shift)]), CellError::Num);
+            }
+            if f == "BITLSHIFT" {
+                is_err(ev(f, vec![n(1.0), n(53.0)]), CellError::Num);
+            } else {
+                close(ev(f, vec![n(1.0), n(53.0)]), 0.0);
+            }
+            is_err(ev(f, vec![n(0.0), t("bad")]), CellError::Value);
+        }
+        is_err(ev("BITRSHIFT", vec![n(-1.0), n(100.0)]), CellError::Num);
     }
 
     #[test]

docs/function-parity.md

@@ -1,6 +1,6 @@
 # Function parity: worksheet functions and formulas
 
-> **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: base conversion rejects surrounding whitespace in source strings, 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
+> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (BITLSHIFT and BITRSHIFT return zero for zero operands with shifts beyond 53 bits, as observed in Excel; earlier: 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).
@@ -126,6 +126,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 |---|---|---|
 | 2026-10-31 | minor | BIN2*, HEX2* and OCT2* reject surrounding spaces and tabs in source strings with `#NUM!`, matching Excel; plain unpadded values remain valid |
 | 2026-10-31 | minor | DEC2BIN, DEC2HEX and DEC2OCT validate `places` before returning negative two's-complement output, and Boolean places return `#VALUE!`, matching Excel |
+| 2026-10-31 | minor | BITLSHIFT and BITRSHIFT return `0` for zero operands shifted beyond 53 bits in either direction; nonzero operands retain the `#NUM!` limit, matching Excel |
 | 2026-10-27 | minor | ECMA.CEILING added to the functions that are in our library but not on Microsoft's list (with USDOLLAR), so the counts don't change |
 | 2026-10-26 | minor | IMSQRT uses Excel's polar route with its cosine reduction, so `IMSQRT("-4")` is `1.22514845490862E-16+2i` as in Excel (exact `2i` before); the rows list the IM* differences still open |
 | 2026-10-25 | minor | LAMBDA row: a LAMBDA that calls itself more than 140 times, and a formula nested past the depth limit, give `#NUM!` (#1809; nesting gave `#CALC!` before). `=Foo(1)` where the defined name Foo holds `#N/A` gives `#N/A`, not `#NAME?` |