Re: [Haskell-cafe] Re: Is logBase right?

You're absolutely right. It would be easy to change logBase to have special cases for, say, base 2 and base 10, and call the C library functions for those. In fact, I think it's a worth while change, since it's easy and get's better results for some cases. -- Lennart On Sun, Aug 23, 2009 at 12:41 PM, Steve wrote:

On Sat, 2009-08-22 at 13:03 -0400, haskell-cafe-request@haskell.org wrote:

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Message: 10 Date: Sat, 22 Aug 2009 11:24:21 +0200 From: Roberto L?pez Subject: [Haskell-cafe] Re: Is logBase right? To: haskell-cafe@haskell.org Message-ID: Content-Type: text/plain; charset="ISO-8859-1"

If 4.0 / 2.0 was 1.9999999999999999999998, it would be ok?

The real value of log10 1000 is 3 (3.0). It can be represented with accuracy and it should be.

You get the accuracy value in Perl, but there is the same problem in Python. It's a bit discouraging.

There is *not* the same problem in Python: $ python Python 2.6.2 (r262:71600, Jul  9 2009, 23:16:53) [GCC 4.4.0 20090506 (Red Hat 4.4.0-4)] on linux2 Type "help", "copyright", "credits" or "license" for more information.

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import math math.log10(1000) 3.0

Recent work in Python 3 (and Python 2.6) has improved the handling of floating point numbers, and addresses exactly the problem that Roberto has raised.

I see no reason why Haskell could not improve its handling of floating point numbers by using similar techniques.

Steve

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