Re: Getting the integer part of a real

[arny@wayback.UUCP (Arny B. Engelson)]

Dave Emery writes:
> 
> When we discovered the 'feature' in Ada that an implementor can pick how
> he rounds, we discussed various ways to get the integer part of a number.
> Here is the 'best' (meaning most portable) way:  (p.s. this 'algorithm' 
> is obviously language-independent)
> 
> 	declare
> 	    x : real;
> 	    i : integer;	-- integer part of x
> 	begin
> 	    i := integer(x);
> 	    if (i > x) then
> 		   -- machine rounded up
>                 i := i - 1;
> 	    end if;
> 	end;
> 

The above algorithm only works for POSITIVE values of X!  For example, if
X = -0.7 this will return -1 instead of 0.  The "integer part of a real number"
is a truncate function:

   function Trunc (X : Float) return Integer is
      I : Integer := Integer (X);
   begin
      if I > 0 and then
	 Float(I) > X then
	    I := I - 1;
      elsif I < 0 and then
	 Float(I) < X then
	    I := I + 1;
      end if;
      return I;
   end Trunc;

This should return whatever is before the decimal point in a floating point
number.

Arny B. Engelson
{ihnp4 | bonnie | clyde } wayback!arny
(201) 386-4816