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Re: Integer promotions, conversions, coercions and templates :(

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From Ian Collins <ian-news@hotmail.com>
Newsgroups comp.lang.c++
Subject Re: Integer promotions, conversions, coercions and templates :(
Date Fri, 10 Jun 2011 07:37:15 +1200
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On 06/10/11 12:30 AM, MikeP wrote:
> Ian Collins wrote:
>> On 06/ 9/11 12:13 PM, MikeP wrote:
>>> Ian Collins wrote:
>>>> On 06/ 9/11 10:09 AM, MikeP wrote:
>>>>> I need help (but nevermind that!) templates and the C++ integer
>>>>> rules are confusing me! (No occifer, I have not been drinking, I am
>>>>> just dazed and confused by C++ integer rules!).
>>>>>
>>>>> // CheckBit
>>>>> // Checks the status of individual bits of any unsigned integer
>>>>> type. // Indexing of bits starts at 1, not 0.
>>>>> // mask can be any unsigned integer type.
>>>>> // W is the width of the type T.
>>>>> //
>>>>> template<typename T, unsigned int W>
>>>>> bool CheckBit(T&    mask, T n)
>>>>> {   // The assertion should be an exception, I know.
>>>>>        Assert((n>= 1)&&    (n<= W), "Bit index out of range.")
>>>>
>>>> Missing semicolon.
>>>>
>>>>>        return ((mask&    ((T)1)<<    (n-((T)1))) != 0);
>>>>> }
>>>>>
>>>>> I wanted to use the appropriate integer type suffix as a template
>>>>> parameter to use on the 1's (don't know if I needed to though), but
>>>>> C++ templates won't allow that so I have the casts-to-T all over
>>>>> the place but I'm not sure if they are necessary.
>>>>
>>>> Why don't you just use
>>>>
>>>>     const T one(1);
>>>>     return (((mask&   one)<<   (n-one)) != 0);
>>>
>>> Adds one move instruction to get '1' into 'one' (which is in a
>>> register) over the cast-to-T implementation (2 move instructions for
>>> 64-bit T), so I'd keep the ugly version. Using the suffix would be
>>> the way to write CheckBit if it wasn't a template:
>>
>> Poor job on the compiler's part!
>>
>> The function should optimise down to 0 or 1.
>
> The example is actually an inline method in a class, but even so, the
> compiler didn't inline it. Weird. (My example should have had the
> "inline" keyword on it also).

That's unnecessary in this case.

> My bad, I'm in debug mode with inlining overridden!

Oops...

> I'll do the release version and repost later. (Still
> educational though from a learning-assembly and code generation
> perspective).
>
> It does seem that templates are trumped by a preprocessor macro this
> time, for the macro does not require a change to the algorithm. Templates
> defficient?

What change to what algorithm?

-- 
Ian Collins

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Thread

Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-08 17:09 -0500
  Re: Integer promotions, conversions, coercions and templates :( Ian Collins <ian-news@hotmail.com> - 2011-06-09 10:22 +1200
    Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-08 17:49 -0500
    Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-08 19:13 -0500
      Re: Integer promotions, conversions, coercions and templates :( Ian Collins <ian-news@hotmail.com> - 2011-06-09 14:32 +1200
        Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-09 07:30 -0500
          Re: Integer promotions, conversions, coercions and templates :( Öö Tiib <ootiib@hot.ee> - 2011-06-09 06:18 -0700
            Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-09 08:45 -0500
              Re: Integer promotions, conversions, coercions and templates :( Öö Tiib <ootiib@hot.ee> - 2011-06-09 06:51 -0700
                Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-09 13:44 -0500
          Re: Integer promotions, conversions, coercions and templates :( Ian Collins <ian-news@hotmail.com> - 2011-06-10 07:37 +1200
            Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-09 15:11 -0500
              Re: Integer promotions, conversions, coercions and templates :( Ian Collins <ian-news@hotmail.com> - 2011-06-10 09:09 +1200
                Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-09 17:15 -0500
                Re: Integer promotions, conversions, coercions and templates :( Ian Collins <ian-news@hotmail.com> - 2011-06-10 10:40 +1200
                Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-10 05:07 -0500
                Re: Integer promotions, conversions, coercions and templates :( Öö Tiib <ootiib@hot.ee> - 2011-06-10 03:14 -0700
                Re: Integer promotions, conversions, coercions and templates :( Öö Tiib <ootiib@hot.ee> - 2011-06-10 03:19 -0700
                Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-10 06:08 -0500
                Re: Integer promotions, conversions, coercions and templates :( Öö Tiib <ootiib@hot.ee> - 2011-06-10 04:32 -0700
                Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-10 07:14 -0500
                Re: Integer promotions, conversions, coercions and templates :( Öö Tiib <ootiib@hot.ee> - 2011-06-10 05:27 -0700
                Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-10 07:35 -0500
                Re: Integer promotions, conversions, coercions and templates :( Öö Tiib <ootiib@hot.ee> - 2011-06-10 06:47 -0700
                Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-10 06:18 -0500
                Re: Integer promotions, conversions, coercions and templates :( Ian Collins <ian-news@hotmail.com> - 2011-06-11 08:08 +1200
                Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-10 18:41 -0500
    Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-10 08:11 -0500
  Re: Integer promotions, conversions, coercions and templates :( Öö Tiib <ootiib@hot.ee> - 2011-06-09 06:28 -0700
    Re: Integer promotions, conversions, coercions and templates :( "MikeP" <mp011011@some.org> - 2011-06-09 08:50 -0500
  Re: Integer promotions, conversions, coercions and templates :( (Summary so far) "MikeP" <mp011011@some.org> - 2011-06-10 08:40 -0500
    Re: Integer promotions, conversions, coercions and templates :( (Summary so far) Öö Tiib <ootiib@hot.ee> - 2011-06-10 07:14 -0700
      Re: Integer promotions, conversions, coercions and templates :( (Summary so far) "MikeP" <mp011011@some.org> - 2011-06-10 09:17 -0500
    Re: Integer promotions, conversions, coercions and templates :( (Summary so far)(Corrections and more) "MikeP" <mp011011@some.org> - 2011-06-10 09:14 -0500
      Re: Integer promotions, conversions, coercions and templates :( (Results: Generated Code) "MikeP" <mp011011@some.org> - 2011-06-10 12:43 -0500
  Re: Integer promotions, conversions, coercions and templates :( (Conclusion) "MikeP" <mp011011@some.org> - 2011-06-14 18:35 -0500
    Re: Integer promotions, conversions, coercions and templates :( (Conclusion) Ian Collins <ian-news@hotmail.com> - 2011-06-15 12:51 +1200
      Re: Integer promotions, conversions, coercions and templates :( (Conclusion) "MikeP" <mp011011@some.org> - 2011-06-15 08:45 -0500
    Re: Integer promotions, conversions, coercions and templates :( (Conclusion) Michael DOUBEZ <michael.doubez@free.fr> - 2011-06-15 03:33 -0700
      Re: Integer promotions, conversions, coercions and templates :( (Conclusion) "MikeP" <mp011011@some.org> - 2011-06-15 09:17 -0500
        Re: Integer promotions, conversions, coercions and templates :( (Conclusion) Michael DOUBEZ <michael.doubez@free.fr> - 2011-06-16 04:17 -0700
          Re: Integer promotions, conversions, coercions and templates :( (Conclusion) "MikeP" <mp011011@some.org> - 2011-06-16 09:45 -0500
            Re: Integer promotions, conversions, coercions and templates :( (Conclusion) Michael DOUBEZ <michael.doubez@free.fr> - 2011-06-17 01:56 -0700
              Re: Integer promotions, conversions, coercions and templates :( (Conclusion) "MikeP" <mp011011@some.org> - 2011-06-17 07:58 -0500
                Re: Integer promotions, conversions, coercions and templates :( (Conclusion) Michael DOUBEZ <michael.doubez@free.fr> - 2011-06-17 06:54 -0700
                Re: Integer promotions, conversions, coercions and templates :( (Conclusion) "MikeP" <mp011011@some.org> - 2011-06-17 09:19 -0500
              Re: Integer promotions, conversions, coercions and templates :( (Conclusion) "MikeP" <mp011011@some.org> - 2011-06-17 08:17 -0500
                Re: Integer promotions, conversions, coercions and templates :( (Conclusion) Michael DOUBEZ <michael.doubez@free.fr> - 2011-06-17 07:33 -0700
                Re: Integer promotions, conversions, coercions and templates :( (Conclusion) "MikeP" <mp011011@some.org> - 2011-06-17 09:49 -0500

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