Improve speed of GetHashCode

src/ISA/ISA/ArcTypes/ArcTable.fs

@@ -780,18 +780,11 @@ type ArcTable(name: string, headers: ResizeArray<CompositeHeader>, values: Syste
     // it's good practice to ensure that this behaves using the same fields as Equals does:
     override this.GetHashCode() = 
         //let v1,v2 = 
-        let v =
-            [|
-                for KeyValue(k,v) in this.Values do
-                    yield k, v
-            |] 
-            |> Array.sortBy fst
-            // must remove tuples. Tuples handle unpredictable for GetHashCode in javascript.
-            |> Array.map (fun ((k1,k2),v) -> [|box k1; box k2; box v|] |> Aux.HashCodes.boxHashArray) 
+        let vHash =  ArcTableAux.boxHashValues this.ColumnCount this.Values
         [|
             box this.Name
-            Array.ofSeq >> Aux.HashCodes.boxHashArray <| this.Headers
-            Array.ofSeq >> Aux.HashCodes.boxHashArray <| v
+            this.Headers |> Aux.HashCodes.boxHashSeq 
+            vHash
         |]
         |> Aux.HashCodes.boxHashArray 
         |> fun x -> x :?> int

src/ISA/ISA/ArcTypes/ArcTableAux.fs

@@ -24,6 +24,15 @@ let getRowCount (values:Dictionary<int*int,CompositeCell>) =
     if values.Count = 0 then 0 else
         values.Keys |> Seq.maxBy snd |> snd |> (+) 1
 
+let boxHashValues colCount (values:Dictionary<int*int,CompositeCell>) =
+    let mutable hash = 0
+    let rowCount = getRowCount values
+    for col = 0 to colCount - 1 do
+        for row = 0 to rowCount - 1 do
+            hash <- 0x9e3779b9 + values.[col,row].GetHashCode() + (hash <<< 6) + (hash >>> 2)
+    hash    
+    |> box
+
 // TODO: Move to CompositeHeader?
 let (|IsUniqueExistingHeader|_|) existingHeaders (input: CompositeHeader) = 
     match input with

tests/ISA/ISA.Tests/ArcTable.Tests.fs

@@ -108,6 +108,13 @@ let private tests_GetHashCode = testList "GetHashCode" [
         let notActual = create_testTable()
         Expect.notEqual actual notActual "equal"
         Expect.notEqual (actual.GetHashCode()) (notActual.GetHashCode()) "Hash"
+    testCase "Performance" <| fun _ ->
+        let testTable = ArcTable.init("Test")
+        let values = Array.init 10000 (fun i -> CompositeCell.createFreeText (string i))
+        testTable.AddColumn(CompositeHeader.FreeText "Header", values)
+        let f1 () = testTable.GetHashCode()
+        // On i7-13800H, 2ms in Dotnet and 18ms in javascript
+        Expect.wantFaster f1 50 "GetHashCode is too slow" |> ignore
 ]
 
 let private tests_validate =