Re: Red-faced professor gets bitten in search for portability

[micro-heart-of-gold.mit.edu!wupost!zaphod.mps.ohio-state.edu!uakari.prima te.wisc.edu!usenet.coe.montana.edu!milton!mfeldman@bloom-beacon.mit.edu (Micha el Feldman)]

In article <daves.690605701@condor> daves@assip.csasyd.oz.au writes:
 [ stuff deleted ]
>
>  FUNCTION Trunc (X: Float) RETURN Integer IS
>  BEGIN
>    RETURN Integer(2.0 * X) / 2;
>  END Trunc;
>
>still takes the integer before the division.  In fact, as you've now doubled t
he
>number, the horrible rounding beast is twice as active (i.e. 0.25 and 0.75
>both fall victim).

Indeed. Oops.
>
>I think Mike Murphy's code looks awkward because it's sort of upside down.  Th
e 
>problem can be restated as: "if integer () rounds up, return one less than the
>value of integer (), otherwise return the value of integer ()".
>
>This translates to:
>
>  function trunc (number: float) return integer is
>  begin
>    if float (integer (number)) > number then  -- does it round up?
>      return integer (number) - 1;             -- yes - stop it!
>    else
>      return integer (number);                 -- no - ok as it is.
>    end if;
>  end trunc;
>
>(I'm assuming that my compiler is clever enough to eliminate the redundant con
versions to integer.)
>

Better and simpler. Portable, too, I think.

Mike Feldman