Question

Is there a case-insensitive variant of the Bob Jenkins hash function?

Generics.Defaults.BobJenkinsHash

provides a fast hash function. Unfortunately it cannot be used in combination with a case-insensitive compare function like so

TCustomStringComparer = class (TEqualityComparer <String>)
  function Equals(const Left, Right: String): Boolean; override;
  function GetHashCode(const Value: String): Integer; override;
end;
function TCustomStringComparer.Equals (const Left, Right : String) : Boolean;
begin
  Result := CompareText (Left, Right) = 0;
end;
function TCustomStringComparer.GetHashCode (const Value : String) : Integer;
begin
  Result := Generics.Defaults.BobJenkinsHash (Value [1], Length (Value) * SizeOf (Char), 0);
end;

This is because TDictionary first compares the hash codes and then uses the provided comparer when checking for equality.

Of course I could use UpperCase in my GetHashCode function, but I wondered if it would be faster if I could somehow modify the hash function itself.

Answer 1

No, there is no case invariant version of the hash function. Lower or upper case all strings before passing them to the hash function.