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Date: Mon, 30 Jul 2012 22:11:41 +0800
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To: Devis Lucato <devis@lucato.it>
Cc: PHP Developers Mailing List <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] bug on bc math?
From: laruence@php.net (Laruence)

On Mon, Jul 30, 2012 at 9:52 PM, Laruence <laruence@php.net> wrote:
> Hi:
>
> I'd like mark this as a doc problem,  see the comment of the bcmatch lib:
>
> /* The multiply routine.  N2 times N1 is put int PROD with the scale of
>    the result being MIN(N2 scale+N1 scale, MAX (SCALE, N2 scale, N1 scale)).
>    */
>     void  bc_multiply (bc_num n1, bc_num n2, bc_num *prod, int scale TSRMLS_DC)
>
> and
>
> * Here is the full add routine that takes care of negative numbers.
>    N1 is added to N2 and the result placed into RESULT.  SCALE_MIN
>    is the minimum scale for the result. */
>
> void  bc_add (n1, n2, result, scale_min)
>
> thanks
Hi:
   but on the hand, we may also consider this as a bug,  behavior not
act like the doc said :)

   any IMO,  fixing this, we should add some logic in PHP side,  like
before returning value to user .

   the code will look like(for bc_multiply):


   if (result->n_scale < scale ) {
       result->n_value =  erealloc($result->n_value, scale);

       memset(result->n_result + result->n_scale, '0', scale - result->n_scale);

       result->n_scale = scale;
   }

   this will be a little ugly, since it alter the bc_num struct which
should only inside bc lib,   what do you think?

thanks
>
> On Mon, Jul 30, 2012 at 8:47 PM, Devis Lucato <devis@lucato.it> wrote:
>> Hi,
>>
>> before raising a bug I was wondering if anyone noticed this odd behavior in
>> BC math functions ?
>>
>> Actual
>>
>> php -r "echo bcmul('1.1', '9.0', 5);" ==> 9.90
>> php -r "bcscale(5); echo bcmul('1.1', '9.0');" ==> 9.90
>> php -r "bcscale(5); echo bcadd('8.9', '1.0');" ==> 9.90000
>>
>>
>> Expected
>>
>> php -r "echo bcmul('1.1', '9.0', 5);" ==> 9.90000
>> php -r "bcscale(5); echo bcmul('1.1', '9.0');" ==> 9.90000
>> php -r "bcscale(5); echo bcadd('8.9', '1.0');" ==> 9.90000
>>
>>
>> Seen on 5.3 and 5.4.
>>
>> Looking at
>> http://git.php.net/?p=php-src.git;a=history;f=ext/bcmath/bcmath.c;h=5dfafa8bd8dbc1703af2ea4452ac2b05b765a619;hb=HEADI
>> couldn't see any recent change related to this bug.
>>
>> Thank you
>
>
>
> --
> Laruence  Xinchen Hui
> http://www.laruence.com/



-- 
Laruence  Xinchen Hui
http://www.laruence.com/