select left('123', 0.5) from rdb$database

select left('123', 2.5) from rdb$database

create or alter procedure bankers_round (
    val double precision,
    rnd_digit integer)
returns (
    res double precision)
as
declare variable v_rnd_digit integer;
declare variable v_remainder integer;
begin
  v_rnd_digit = trunc(rnd_digit);
  v_remainder = (val - trunc(val, v_rnd_digit)) * power(10, v_rnd_digit + 1);
  if (abs(v_remainder) < 5 or abs(v_remainder) = 5 and
      mod(trunc(val * power(10, v_rnd_digit)), 2) = 0) then
    res = trunc(val, v_rnd_digit);
  else
    res = round(val, v_rnd_digit);
  suspend;
end