Re: C fmod function

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 12 Apr 2006 15:49:36 GMT, Candida Ferreira wrote:

> Dmitry A. Kazakov wrote:
>>> Is there in Ada a built-in function equivalent to the fmod function in 
>>> C++?
>>
>> Yes. See Annex A.5.3, Remainder attribute defined for floating-point 
>> types.
> 
> Thanks, Dmitry. I was aware of the Remainder attribute, but having read the 
> definition I wasn't sure if it corresponded exactly to the C++ fmod function 
> which can be represented by the generic expression fMod(x,y) = ((x / y) - 
> (Sign(x / y) * Floor(Abs(x / y)))) * y.

Yes, you are right. The above rounds towards zero and the result has the
sign of x. Ada's remainder rounds to the nearest number, so the sign can be
any and the result's absolute value is no greater than |y/2|.

You can convert it to fmod as follows:

f := S'Remainder (x, y);
if Sign (x) = Sign (f) then
   return f;
elsif Sign (y) = Sign (f) then
   return f - y;
else
   return f + y;
end if;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de