Re: [Boost-users] Boost.MultiIndex question on merge

Subject: Re: [Boost-users] Boost.MultiIndex question on merge
From: arm2arm (arm2arm_at_[hidden])
Date: 2009-04-28 13:42:19

Thanks Ovanes for explanations, I did not touched MSVC ages currently I am
using g++ and icpc:
Probably intel also provides its own STL optimized library, I am not an
expert, but always the fast gooling gives that in the intel presentations
they avoiding usage of for_each, I will try to bench the part of the code to
see which approach is faster in my case insert or for_each.
But I am running in to trouble with inserter:

struct strData{
int id;
float a, b;
strData(int id_, float a_, float b_):a(a_),b(b_),id(id_){}
};

typedef multi_index_container<
   strData,
   indexed_by<
   ordered_unique<
   tag<id>,  BOOST_MULTI_INDEX_MEMBER(strData,int,id)>,
   ordered_non_unique<
   tag<snap>,BOOST_MULTI_INDEX_MEMBER(strData,float,a)>
   > indexed_data_type;

indexed_data_type  data_setA, data_setB;// we need append setB to setA

{
scoped_timer timeme("merge by INSERT: ");
data_setA.insert(data_setB.begin(), data_setB.end());
}

{
scoped_timer timeme("merge by FOR_EACH: ");
 std::for_each(
                    data_setB.begin(),
                    data_setB.end(),std::inserter(data_setA));
}

The compiler gives long error on:
error: no matching function for call to
'inserter(boost::multi_index::multi_index_container etc....

What is the correct syntax of the inserter with multi_index_container ?

Thanks 
Arman.

Ovanes Markarian wrote:
> 
> On Tue, Apr 28, 2009 at 5:05 PM, arm2arm <arm2arm_at_[hidden]> wrote:
> 
>>
>> To: Ovanes
>> Are there gain in the speed if  I would use the for_each?
>> I am always avoiding to use for_each  to allow the compiler (like INTEL)
>> auto-parallelize the regions.
>> But for this particular case Is not a issue.
>>
> 
> to be honest, that's strange. I know from MSVC that using std::algorithms
> allows parallelisation.
> 
> e.g. using std::find of a 32bit numeric value in a vector runs up to 4
> times
> faster, due to XMM register optimization. Copying out the std::find loop
> implemation runs slower, since the compiler does not know how the vector
> pointed by pointer/iterator is aligned. It is pretty well explained here:
> http://www.agner.org/optimize/optimizing_cpp.pdf Chapter 11. My
> experiments
> with MSVC 2003 & 2005 show that searching for a number (with is not
> present
> in the vector) in a loop copied from find impl is 4 times slower as using
> find itself. I am curious how it is with Intel compiler.
> 
> IMO STL algorithms delivered with compiler are pretty well optimized for
> that particular compiler version. If you write your loop, it is for sure
> not
> faster as comaprible STL algo distributed with the compiler. Does Intel
> explicitly state that they do not optimize STL code and it is not parallel
> nor the STL does not use XMM registers?
> 
> 
> Thanks,
> Ovanes
> 
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
> 

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