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Groups > comp.lang.c++ > #6496
| From | "MikeP" <mp011011@some.org> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: Integer promotions, conversions, coercions and templates :( |
| Date | 2011-06-09 08:45 -0500 |
| Organization | A noiseless patient Spider |
| Message-ID | <isqipn$d22$1@dont-email.me> (permalink) |
| References | (1 earlier) <95ab12FrnrU6@mid.individual.net> <isp36q$7sb$1@dont-email.me> <95apmqFrnrU10@mid.individual.net> <isqee8$iru$1@dont-email.me> <33f9545c-7aa5-4ee5-ba45-65ce53dcc3c7@f11g2000vbx.googlegroups.com> |
Öö Tiib wrote:
> On Jun 9, 3:30 pm, "MikeP" <mp011...@some.org> 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). My bad, I'm in debug mode with inlining
>> overridden! 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?
>
> You are in debugging mode evaluating performance of compiler-generated
> code?
No, read the post from the beginning. The post is about the "impedance
mismatch" between templates and the C++ type system.
> Worthless waste of time. Turn all optimizations that you plan to
> use in production code on. Otherwise you get wrong impression what
> compiler will really do.
Reread what I wrote above! Geez, what an opportunist.
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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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