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Date: Fri, 2 Apr 2004 12:07:59 -0800
From: David Brown <caml-list@davidb.org>
To: Zeno Lee <zeno.lee@earthlink.net>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] weird floating poing behavior on windows
Message-ID: <20040402200759.GA12200@davidb.org>
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On Fri, Apr 02, 2004 at 02:39:43PM -0500, Zeno Lee wrote:
> Can anyone tell me what's going on here?  Is this a known issue on windows? 
> 
> C:\>ocaml
>         Objective Caml version 3.07+2
> # 0.2 *. 0.26;;
> - : float = 0.052000000000000005
> # 0.8 *. 0.7 *. 0.8;;
> - : float = 0.44799999999999995

Nothing unusual.  Floats only have a certain amount of precision.  The
toplevel prints floats out with more precision than they contain.  It
does the same thing on Linux.

For example, in C:

        #include <stdio.h>

        int
        main (int argc, char **argv)
        {
          printf ("%.17g\n", 0.2 * 0.26);
          printf ("%.17g\n", 0.8 * 0.7 * 0.8);
          return 0;
        }

prints:
        0.052000000000000005
        0.44799999999999995

Now the real question is why does the toplevel do this (and where, in
the code is it coming from).  string_of_float only uses 12 digits.

Dave Brown

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