Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!hp4nl!dutrun!winfave
From: winfave@dutrun.UUCP (Alexander Verbraeck)
Newsgroups: comp.lang.pascal
Subject: Re: TP 5.5  int() function
Keywords: TP,Turbo,Pascal
Message-ID: <1864@dutrun.UUCP>
Date: 16 Aug 90 11:46:52 GMT
References: <1990Aug15.160719.12762@ux1.cso.uiuc.edu>
Reply-To: winfave@dutrun.UUCP (A.Verbraeck)
Distribution: comp
Organization: Delft University of Technology, The Netherlands
Lines: 56

In article <1990Aug15.160719.12762@ux1.cso.uiuc.edu> aindiana@osiris.cso.uiuc.edu (Daiv Stoner) writes:
>
>
>A little technical question for all you net wizards.
>The following piece of code written and compiled in Turbo Pascal
>5.5 on an IBM Model 50 gives strange results.
>
>Here's the code:
>
>program a;
>var
> rate,reg:real;
>  x,value:real;
>begin
>  rate:=2.01;
>  reg:=12.5;
>  value:=rate*reg*100+0.5;
>  x := int(value)/100;
>
>writeln('rate=',rate:8:4,'  reg=',reg:8:4,'  total=',rate*reg:8:4,'  x=',x:8:4);
>end.
>
>I get this output:
>
>rate=  2.0100  reg= 12.5000  total= 25.1250  x= 25.1200
>
>Borland Tech. Support says "round-off" error.  I say it's a bug.
>Any ideas?
>

I think Borland Tech Support is right: it's a "roud off" error. The
Int() function "Returns the integer part of the argument" according to
page 321 of my TP 5.5 manual. As real values are not stored in decimal
form, but in binary form, it might be that 2.01*12.5*100+0.5 will be
stored as the equivalent of 2512.99999999. The value of
Int(2512.99999999) is, however sadly in this case, 2512 instead of 2513,
the value you would expect. A possible solution: use Int(value+epsilon)
instead of Int(value), with epsilon a value that is very small, for
instance covering only one or two of the least significant bits. This is
especially important in financial programs, as I once found out the hard
way. You'll be loosing cents in no time, when you store financial values
as reals, and then perform arithmetic on them. Solution: either use
(long)ints, or apply the epsilon-trick. I used a function "CleanMoney"
for that, that looked something like this:

function CleanMoney(m:real):real;
begin
  CleanMoney:=Int(100.0*m+epsilon)/100.0;
end;

----------------------------------------------------------------------
Alexander Verbraeck                  e-mail: winfave@dutrun.tudelft.nl
Delft University of Technology               winfave@hdetud1.bitnet
Department of Information Systems            winfave@dutrun.uucp
PO Box 356, 2600 AJ  The Netherlands         dutrun!winfave@hp4nl.uucp
----------------------------------------------------------------------