G717: cap binomial trial counts

crates/functions/src/stat/distributions.rs

@@ -71,6 +71,8 @@ fn f_pdf(x: f64, d1: f64, d2: f64) -> f64 {
     ((d1 / 2.0) * (d1 / d2).ln() + (d1 / 2.0 - 1.0) * x.ln() - ((d1 + d2) / 2.0) * (1.0 + d1 * x / d2).ln() - ln_beta(d1 / 2.0, d2 / 2.0)).exp()
 }
 
+const MAX_BINOM_TRIALS: f64 = 2_147_483_646.0;
+
 fn binom_pmf(k: f64, n: f64, p: f64) -> f64 {
     if k < 0.0 || k > n {
         return 0.0;
@@ -407,7 +409,7 @@ pub(super) fn binom_dist(a: &[Arg], _: C) -> R<Value> {
     let n = num(a, 1)?.trunc();
     let p = num(a, 2)?;
     let cum = boolean(a, 3)?;
-    if k < 0.0 || k > n || !(0.0..=1.0).contains(&p) {
+    if k < 0.0 || n > MAX_BINOM_TRIALS || k > n || !(0.0..=1.0).contains(&p) {
         return Err(CellError::Num);
     }
     num_val(if cum { binom_cdf(k, n, p) } else { binom_pmf(k, n, p) })
@@ -418,7 +420,7 @@ pub(super) fn binom_dist_range(a: &[Arg], _: C) -> R<Value> {
     let p = num(a, 1)?;
     let s1 = num(a, 2)?.trunc();
     let s2 = if has(a, 3) { num(a, 3)?.trunc() } else { s1 };
-    if !(0.0..=1e15).contains(&n) || !(0.0..=1.0).contains(&p) || s1 < 0.0 || s1 > n || s2 < s1 || s2 > n {
+    if !(0.0..=MAX_BINOM_TRIALS).contains(&n) || !(0.0..=1.0).contains(&p) || s1 < 0.0 || s1 > n || s2 < s1 || s2 > n {
         return Err(CellError::Num);
     }
     if s2 - s1 > 10_000.0 {

crates/functions/src/stat/tests.rs

@@ -427,7 +427,15 @@ fn discrete() {
     close_tol(ev("BINOM.DIST", vec![n(6.0), n(10.0), n(0.5), b(false)]), 0.205078125, 1e-12);
     close_tol(ev("BINOM.DIST", vec![n(6.0), n(10.0), n(0.5), b(true)]), 0.828125, 1e-12);
     close_tol(ev("BINOMDIST", vec![n(6.0), n(10.0), n(0.5), b(false)]), 0.205078125, 1e-12);
+    close(ev("BINOM.DIST", vec![n(1.0), n(2_147_483_646.0), n(0.0), b(false)]), 0.0);
+    close(ev("BINOM.DIST", vec![n(1.0), n(2_147_483_646.9), n(0.0), b(false)]), 0.0);
+    is_err(ev("BINOM.DIST", vec![n(1.0), n(2_147_483_647.0), n(0.0), b(false)]), CellError::Num);
+    is_err(ev("BINOM.DIST", vec![n(1.0), n(2_147_483_647.9), n(0.0), b(false)]), CellError::Num);
     is_err(ev("BINOM.DIST", vec![n(11.0), n(10.0), n(0.5), b(false)]), CellError::Num);
+    close(ev("BINOM.DIST.RANGE", vec![n(2_147_483_646.0), n(0.0), n(1.0)]), 0.0);
+    close(ev("BINOM.DIST.RANGE", vec![n(2_147_483_646.9), n(0.0), n(1.0)]), 0.0);
+    is_err(ev("BINOM.DIST.RANGE", vec![n(2_147_483_647.0), n(0.0), n(1.0)]), CellError::Num);
+    is_err(ev("BINOM.DIST.RANGE", vec![n(2_147_483_647.9), n(0.0), n(1.0)]), CellError::Num);
     close_tol(ev("BINOM.DIST.RANGE", vec![n(60.0), n(0.75), n(48.0)]), 0.083974967, 1e-6);
     close_tol(ev("BINOM.DIST.RANGE", vec![n(60.0), n(0.75), n(45.0), n(50.0)]), 0.523629793, 1e-6);
     close(ev("BINOM.INV", vec![n(6.0), n(0.5), n(0.75)]), 4.0);

docs/function-parity.md

@@ -1,6 +1,6 @@
 # Function parity: worksheet functions and formulas
 
-> **Last reviewed:** 2026-10-15 · **Last updated:** 2026-10-25 · **Change:** minor (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 (BINOM.DIST and BINOM.DIST.RANGE refuse trial counts above 2,147,483,646 after truncation) · **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).
@@ -97,6 +97,10 @@ This improves series preparation; it does not change the model-fitting or season
 
 ## Depth (estimated)
 
+| Function | Excel parity note |
+|---|---|
+| BINOM.DIST / BINOM.DIST.RANGE | Trial count is truncated, then must be at most 2,147,483,646; larger trials return `#NUM!`. |
+
 **~82% ready.** The library is broad and has 96 test functions in `crates/functions` with many
 assertions each, but there is no conformance suite against Excel-computed results, and user
 reports keep finding edge cases: MIN() with no arguments (#138), COUNTBLANK past the used range
@@ -123,6 +127,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-31 | minor | BINOM.DIST and BINOM.DIST.RANGE reject trial counts above 2,147,483,646 after truncation |
 | 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?` |
 | 2026-10-23 | minor | Number text coercion (VALUE, arithmetic, typed entry): a dollar sign before accounting parentheses (`$(1,234)`, `$ (5)`) and a percent sign after them (`(5)%`) read as negatives; `(-5)`, `((5))`, `($-5)`, `$5%`, `$(5)%` and dates or times in parentheses are `#VALUE!`, as observed in Excel 365 |
 | 2026-10-23 | minor | INDEX with only a row index on a reference of several rows and columns (`INDEX(A1:C3,2)`, `INDEX(A1:C3,0)`) is `#REF!`, as observed in Excel, so it also fails as a range endpoint and inside other functions; an empty column argument (`INDEX(A1:C3,2,)`) still gives the row. Checked that a column array with one index stays a 1×1 array (`TYPE` 64), which is what Excel returns |