* patch by Alexander (Rouse_) Bagel: TArrayHelper.BinarySearch, when searching

    for an element that is obviously missing from the array, should return
    the position where the element should have been, but instead it reset AFoundIndex to -1, resolves #40867

packages/rtl-generics/src/generics.collections.pas

@@ -1335,17 +1335,11 @@ begin
 
     // deferred test for equality
 
+  AFoundIndex := imin;
   LCompare := AComparer.Compare(AValues[imin], AItem);
-  if (imax = imin) and (LCompare = 0) then
-  begin
-    AFoundIndex := imin;
-    Exit(True);
-  end
-  else
-  begin
-    AFoundIndex := -1;
-    Exit(False);
-  end;
+  Result := (imax = imin) and (LCompare = 0);
+  if not Result and (LCompare < 0) then
+    Inc(AFoundIndex);
 end;
 
 { TEnumerator<T> }

tests/tbs/tb0716.pp

@@ -0,0 +1,81 @@
+program tbs9001;
+
+{$mode Delphi}
+
+uses
+  SysUtils,
+  Generics.Collections,
+  Generics.Defaults,
+  Math;
+
+type
+  TStackParam = record
+    Base, Limit: QWord;
+  end;
+
+var
+  List: TList<TStackParam>;
+  S: TStackParam;
+  Index: SizeInt;
+begin
+  List := TList<TStackParam>.Create(TComparer<TStackParam>.Construct(
+    function (const A, B: TStackParam): Integer
+    begin
+      Result := IfThen(A.Limit < B.Limit, -1,
+        IfThen(A.Limit = B.Limit, 0, 1));
+    end)
+  );
+  try
+    S.Limit := 100;
+    S.Base := 200;
+    List.Add(S);
+
+    S.Limit := 210;
+    S.Base := 300;
+    List.Add(S);
+
+    S.Limit := 350;
+    S.Base := 400;
+    List.Add(S);
+
+    S.Limit := 50;
+    if List.BinarySearch(S, Index) or (Index <> 0) then
+      Halt(1);
+
+    S.Limit := 100;
+    if not List.BinarySearch(S, Index) or (Index <> 0) then
+      Halt(2);
+
+    S.Limit := 150;
+    if List.BinarySearch(S, Index) or (Index <> 1) then
+      Halt(3);
+
+    S.Limit := 210;
+    if not List.BinarySearch(S, Index) or (Index <> 1) then
+      Halt(4);
+
+    S.Limit := 290;
+    if List.BinarySearch(S, Index) or (Index <> 2) then
+      Halt(5);
+
+    S.Limit := 340;
+    if List.BinarySearch(S, Index) or (Index <> 2) then
+      Halt(6);
+
+    S.Limit := 350;
+    if not List.BinarySearch(S, Index) or (Index <> 2) then
+      Halt(7);
+
+    S.Limit := 360;
+    if List.BinarySearch(S, Index) or (Index <> 3) then
+      Halt(8);
+
+    S.Limit := 450;
+    if List.BinarySearch(S, Index) or (Index <> 3) then
+      Halt(9);
+
+  finally
+    List.Free;
+  end;
+end.
+