From bug-request at octave dot org Thu Jan 27 10:42:20 2005
Subject: Re: dec2base bug?
From: David Bateman <David dot Bateman at motorola dot com>
To: Andre Girard <andre at inrs-emt dot uquebec dot ca>
Cc: bug-octave at bevo dot che dot wisc dot edu
Date: Thu, 27 Jan 2005 17:43:36 +0100

This is a multi-part message in MIME format.
--------------080707070305070707030908
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

David Bateman wrote:

> Andre Girard wrote:
>
>> octave:18> version
>> ans = 2.1.57
>> octave:19> for i=1:9
>> > dec2base(10^i,10)
>> > end
>> ans = 10
>> ans = 100
>> ans = 000
>> ans = 10000
>> ans = 100000
>> ans = 000000
>> ans = 10000000
>> ans = 100000000
>> ans = 000000000
>
>
>
> This is a rounding error in the calculation of the number of digits in 
> the string. However, its quite complicated to see how to treat this 
> problem directly as consider cases like dec2base(2^53-1,2) since due 
> to IEEE754 rounding errors log(2^53-1) is exactly log(2^53). In fact 
> the only way I see of treating this is to allow that there might be an 
> extra digit, and then check if it was used and remove it at the end...
>
> The following patch does that.... Anyone have a better solution
>
> D.
>

Opps, I forgot a ";" in my patch.. Use the attached version instead

D.



-- 
David Bateman                                David dot Bateman at motorola dot com
Motorola CRM                                 +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 1 69 35 77 01 (Fax) 
91193 Gif-Sur-Yvette FRANCE

The information contained in this communication has been classified as: 

[x] General Business Information 
[ ] Motorola Internal Use Only 
[ ] Motorola Confidential Proprietary


--------------080707070305070707030908
Content-Type: text/plain;
 name="patch.dec2base-20050127"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="patch.dec2base-20050127"

*** dec2base.m.orig	2005-01-27 16:57:36.640980791 +0100
--- dec2base.m	2005-01-27 17:42:11.609995203 +0100
***************
*** 73,80 ****
      error ("dec2base: base must be between 2 and 36 or a string of symbols");
    endif
    
!   ## determine number of digits required to handle all numbers
!   max_len = floor (log (max (max (n), 1)) ./ log (base)) + 1;
  
    if (nargin == 3)
      max_len = max (max_len, len);
--- 73,81 ----
      error ("dec2base: base must be between 2 and 36 or a string of symbols");
    endif
    
!   ## determine number of digits required to handle all numbers, can overflow
!   ## by 1 digit
!   max_len = round (log (max (max (n), 1)) ./ log (base)) + 1;
  
    if (nargin == 3)
      max_len = max (max_len, len);
***************
*** 88,91 ****
--- 89,97 ----
    ## convert digits to symbols
    retval = reshape (symbols (digits+1), size (digits));
  
+   ## Check if the first element is the zero symbol
+   if (all (retval(:,1) == symbols(1)))
+     retval = retval(:,2:end);
+   endif
+ 
  endfunction

--------------080707070305070707030908--



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
-------------------------------------------------------------