Re: implicit promotion

From	Pete Becker <pete@versatilecoding.com>
Organization	Roundhouse Consulting, Ltd.
Newsgroups	comp.lang.c++
Date	2011-05-30 09:07 -1000
Message-ID	<2011053009075475971-pete@versatilecodingcom> (permalink)
References	<irusp0$6pi$1@reader1.panix.com> <2011053008582491296-pete@versatilecodingcom> <0221c077-9b0c-4953-9be2-71ef9298864a@t16g2000vbi.googlegroups.com>
Subject	Re: implicit promotion

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On 2011-05-30 09:01:48 -1000, Öö Tiib said:

> On May 30, 9:58 pm, Pete Becker <p...@versatilecoding.com> wrote:
>> On 2011-05-30 02:49:08 -1000, Öö Tiib said:
>> 
>> 
>> 
>> 
>> 
>>> On May 30, 2:45 pm, Juha Nieminen <nos...@thanks.invalid> wrote:
>>>> Paavo Helde <myfirstn...@osa.pri.ee> wrote:
>>>>>> If you write
>> 
>>>>>> float tot = (float)sum/tally->size();
>> 
>>>>>> you then have a float divided by an int, 1.5.
>> 
>>>>> Yes, for getting floating-point division one needs to cast only one
>>>>> operand to a floating-point type, the other would be cast to the type of
>>>>> the first automatically. In the original line from OP both operands were
>>>>> cast, possibly because the original author liked symmetry or clarity.
>> 
>>>>   Actually, if a float is divided by an int, aren't both of them cast
>>>> to double first? (Not that it probably makes any difference in practice,
>>>> but just pointing out.)
>> 
>>> Most things about floating point arithmetics is implementation defined
>>> so what really happens depends on platform and compiler.
>> 
>> Not here. Read about "usual arithmetic conversions". If one argument is
>> float and the other is int, the int is converted to float.
> 
> Or into something bigger and more precise if implementation wants. Or
> that is how i read the 5/10 in "usual arithmetic conversions".

No, the type of the result is float. There is general license to do 
floating-point math at higher precision, but that doesn't affect the 
type of the result.

void f(float);
void f(double);

f(1.0f/3);	// calls f(float)

The relevant wording is [emphasis added]:

	Otherwise, if either operand is float, the other *shall be* converted 
to float.

-- 
  Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The 
Standard C++ Library Extensions: a Tutorial and Reference 
(www.petebecker.com/tr1book)

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Thread

implicit promotion Ruben Safir <ruben@mrbrklyn.com> - 2011-05-30 01:44 +0000
  Re: implicit promotion red floyd <no.spam.here@its.invalid> - 2011-05-29 20:35 -0700
    Re: implicit promotion ruben safir <ruben@mrbrklyn.com> - 2011-05-30 00:01 -0400
      Re: implicit promotion Ian Collins <ian-news@hotmail.com> - 2011-05-30 16:08 +1200
        Re: implicit promotion Paavo Helde <myfirstname@osa.pri.ee> - 2011-05-30 01:18 -0500
          Re: implicit promotion Juha Nieminen <nospam@thanks.invalid> - 2011-05-30 11:45 +0000
            Re: implicit promotion Öö Tiib <ootiib@hot.ee> - 2011-05-30 05:49 -0700
              Re: implicit promotion Pete Becker <pete@versatilecoding.com> - 2011-05-30 08:58 -1000
                Re: implicit promotion Öö Tiib <ootiib@hot.ee> - 2011-05-30 12:01 -0700
                Re: implicit promotion Öö Tiib <ootiib@hot.ee> - 2011-05-30 12:07 -0700
                Re: implicit promotion Pete Becker <pete@versatilecoding.com> - 2011-05-30 09:07 -1000
                Re: implicit promotion Öö Tiib <ootiib@hot.ee> - 2011-05-30 12:13 -0700
                Re: implicit promotion Pete Becker <pete@versatilecoding.com> - 2011-05-30 09:27 -1000
            Re: implicit promotion Paavo Helde <myfirstname@osa.pri.ee> - 2011-05-30 10:17 -0500
              Re: implicit promotion Juha Nieminen <nospam@thanks.invalid> - 2011-05-30 18:20 +0000
                Re: implicit promotion Paavo Helde <myfirstname@osa.pri.ee> - 2011-05-30 14:06 -0500
                Re: implicit promotion Pete Becker <pete@versatilecoding.com> - 2011-05-30 09:23 -1000
                Re: implicit promotion Pete Becker <pete@versatilecoding.com> - 2011-05-30 09:29 -1000
                Re: implicit promotion Ruben Safir <ruben@mrbrklyn.com> - 2011-05-31 01:24 +0000
                Re: implicit promotion Ian Collins <ian-news@hotmail.com> - 2011-05-31 13:30 +1200
                Re: implicit promotion ruben safir <ruben@mrbrklyn.com> - 2011-05-31 00:52 -0400
                Re: implicit promotion Pete Becker <pete@versatilecoding.com> - 2011-05-30 17:36 -1000
              Re: implicit promotion Öö Tiib <ootiib@hot.ee> - 2011-05-30 11:39 -0700
                Re: implicit promotion Pete Becker <pete@versatilecoding.com> - 2011-05-30 09:02 -1000

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