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From: arny@wayback.UUCP (Arny B. Engelson)
Newsgroups: net.lang.ada
Subject: Re: Getting the integer part of a real
Message-ID: <996@wayback.UUCP>
Date: Fri, 7-Nov-86 09:27:50 EST
Article-I.D.: wayback.996
Posted: Fri Nov  7 09:27:50 1986
Date-Received: Sat, 8-Nov-86 06:42:59 EST
References: <38000034@gypsy.UUCP>
Organization: AT&T Bell Labs, Whippany, NJ
Summary: This only works for POSITIVE numbers!
List-Id: <comp.lang.ada>

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