gc-fix-2657: isolate PERCENTRANK parity fix

crates/functions/src/stat/descriptive.rs

@@ -336,6 +336,10 @@ pub(super) fn percentrank_impl(a: &[Arg], exc: bool) -> R<Value> {
     if sig < 1.0 || s.is_empty() {
         return Err(CellError::Num);
     }
+    // Excel: 10^significance overflows from 309 up.
+    if sig >= 309.0 {
+        return Err(CellError::Div0);
+    }
     let (first, last) = (s.first().copied().unwrap_or(0.0), s.last().copied().unwrap_or(0.0));
     if x < first || x > last {
         return Err(CellError::NA);
@@ -359,6 +363,10 @@ pub(super) fn percentrank_impl(a: &[Arg], exc: bool) -> R<Value> {
         let (rl, rh) = (rank_of(lo), rank_of(hi));
         rl + (x - lo) / (hi - lo) * (rh - rl)
     };
+    // From significance 15 up Excel returns 15 significant digits, rounded.
+    if sig >= 15.0 {
+        return num_val(format!("{r:.14e}").parse().unwrap_or(r));
+    }
     num_val(trunc_digits(r, sig))
 }
 

crates/functions/src/stat/tests.rs

@@ -214,10 +214,19 @@ fn percentiles() {
     close(ev("PERCENTRANK.EXC", vec![e9.clone(), n(5.43)]), 0.381);
     close(ev("PERCENTRANK.EXC", vec![e9, n(5.43), n(1.0)]), 0.3);
     let t = c(&[1.0, 2.0, 3.0]);
-    close(ev("PERCENTRANK", vec![t.clone(), n(2.0), n(400.0)]), 0.5);
-    close(ev("PERCENTRANK.INC", vec![t.clone(), n(2.0), n(400.0)]), 0.5);
-    close(ev("PERCENTRANK.INC", vec![t.clone(), n(1.0), n(400.0)]), 0.0);
-    close(ev("PERCENTRANK.EXC", vec![t, n(2.0), n(400.0)]), 0.5);
+    // Excel 16: significance 309 and up is #DIV/0!, 308 still works.
+    for name in ["PERCENTRANK", "PERCENTRANK.INC", "PERCENTRANK.EXC"] {
+        is_err(ev(name, vec![t.clone(), n(2.0), n(309.0)]), CellError::Div0);
+        is_err(ev(name, vec![t.clone(), n(1.0), n(400.0)]), CellError::Div0);
+        close(ev(name, vec![t.clone(), n(2.0), n(308.0)]), 0.5);
+    }
+    // From significance 15 up the result has 15 significant digits.
+    let k = c(&[1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0]);
+    for sig in [15.0, 16.0, 308.0] {
+        close_tol(ev("PERCENTRANK.INC", vec![k.clone(), n(2.123_456_789), n(sig)]), 0.187_242_798_166_667, 1e-16);
+    }
+    close(ev("PERCENTRANK.INC", vec![k.clone(), n(2.123_456_789), n(14.0)]), 0.187_242_798_166_66);
+    close(ev("PERCENTRANK.EXC", vec![k, n(2.123_456_789), n(16.0)]), 0.265_432_098_625);
 }
 
 #[test]

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:** 2026-10-30 · **Last updated:** 2026-10-30 · **Change:** minor (function edge-case parity row; 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
 
 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).
@@ -90,6 +90,7 @@ This improves series preparation; it does not change the model-fitting or season
 | LET, LAMBDA, named LAMBDAs, ISOMITTED, MAP/REDUCE/SCAN/BYROW/BYCOL/MAKEARRAY | done. A LAMBDA that calls itself more than 140 times, or a formula nested past the depth limit, gives `#NUM!` (the target app allows deeper recursion, #1581). Calling a defined name that holds an error value gives that error, not `#NAME?` |
 | Iterative calculation for circular references | done: with Enable Iterative Calculation on (`formulas.calculationOptions` `{iterative, maxIterations, maxChange}`, saved as `<calcPr iterate iterateCount iterateDelta>`), loops are evaluated again from their previous values (blank = 0) until no cell on a loop changes by Maximum Change or Maximum Iterations is reached; off, cycles give `#CIRC!`. Set in File › Options › Formulas (Enable iterative calculation, Maximum Iterations 1 to 32767, Maximum Change 0 or more; the two fields are disabled while iteration is off). Differences: GridCraft recalculates on open, so a loop that never settles (`=A1+1`) advances again each time the file is opened
 | 15-significant-digit comparison semantics | done (#57): `=0.1+0.2=0.3` is TRUE, and MATCH and COUNTIF compare the same way. Arithmetic keeps full precision, as Excel does — `=(0.1+0.2)-0.3` is 5.55E-17 |
+| PERCENTRANK significance and precision | done: Excel 16.0 returns `#DIV/0!` from significance 309, and rounds to 15 significant digits for significance 15–308 |
 | External workbook references (`[Book.xlsx]Sheet1!A1`) | parsed; links dropped on open, no update |
 | Localized function names and `;` separators | **missing** (#45); en-US only |
 | Long flat operator chains (`=A1+A2+…`, `-`, `*`, `/`, `^`, `&`, comparisons) | done: no operand limit below Excel's 8,192-character formula limit (Excel, observed: `=1+1+…` with 4,096 operands is exactly 8,192 characters with the `=` and calculates; one more character is refused). Evaluated (#484), printed (#628), stored, copied, adjusted, saved and reopened without recursing once per operand, on a 1 MiB stack (#916); written to XLSX as plain formulas, not dynamic arrays; Spanish entry accepts them |
@@ -123,6 +124,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-30 | minor | Added a function edge-case parity row. |
 | 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 |