uses math;
 
function IsStrMatch(s1, s2: String): Double;
var
  i, iMin, iMax, iSameCount: Integer;
begin
  iMax := Max(Length(s1), Length(s2));
  iMin := Min(Length(s1), Length(s2));
  iSameCount := - 1;
  for i := 0 to iMax do
  begin
    if i > iMin then
      break;
    if s1[i] = s2[i] then
      Inc(iSameCount)
    else
      break;
  end;
  if iSameCount > 0 then
    Result := (iSameCount / iMax) * 100
  else
    Result := 0.00;
end;