Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!apple!das
From: das@Apple.COM (David Shayer)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Why can't the Mac add?
Message-ID: <45072@apple.Apple.COM>
Date: 24 Sep 90 01:17:19 GMT
References: <45060@apple.Apple.COM> <1990Sep23.061645.17161@d.cs.okstate.edu>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 30

I guess I should have been clearer in my last posting, and
I wouldn't have gotten flamed in my email.  I was asking about
this code:
>> main ()
>> {
>>      float   x;
>>
>>      for (x=0.0;x!=10.0;x+=0.2)
>>              printf ("x=%f \n",x);
>> }
I am not using this code in any program.  I would not use a
!= test in a real program, I would use a <.  I understand
that 0.2 does not convert perfectly to binary, and thus 
precision is lost.

I had thought that the reason people wrote complex floating
point software like SANE was to fix situations like this
by have bits indicating that a numerical pattern repeated
indefinitely.  

Suppose you calculated two real numbers, and you wanted to see 
if the results were the same. It seems that you could never 
use a simple equality (==) test, as that would often fail even when
the numbers were the same when calculated with infinite precision.
I take it from people's responses that this problem has not
been solved, even with SANE.
Is there a better way than simply seeing if the numbers are
sufficiently close?  

David