Re: [boost] Improving efficiency of multi_array

From: Ronald Garcia (garcia_at_[hidden])
Date: 2006-12-07 15:24:27

Hi Korcan,

Your proposals for improving multi_array's performance sound  
interesting.  Unfortunately I don't have time right now to pursue  
this, but I am interested in improving multi_array's performance.  If  
you make these changes to your copy of Boost and experience  
performance improvements (without breaking regressions :) ), feel  
free to send me patches and I will see about applying them to the  
library.

Thanks,
ron

On Dec 1, 2006, at 5:24 AM, Korcan Hussein wrote:

> I had a look into multi_array's implementation and i can see a  
> number of opportunities to improve  the efficiency multi_array  
> perhaps by quite a lot with only very minor changes.
>
> Why are we not taking advantage of the fact that that allocation/de- 
> allocation is separate from construction/destruction? i see in a  
> number of places that multi_array is redundantly default  
> constructing elements (like in multi_array::allocate_space) and  
> then copying new elements into the array for example in multi_array  
> i see a lot of:
>
> allocate_space();  // allocate memory then default construct
> std::copy(rhs.begin(),rhs.end(),this->begin());
>
> instead why not just do an in-place copy construction from the  
> outset, something like:
>
> allocate_space(); // a new version which only allocates memory, no  
> construction
> std::uninitialized_copy(rhs.begin(), rhs.end(), this->begin());
>
> When i create a multi_array i want to be able to "reserve" the  
> shape of  a multi_array and then incrementally add new elements via  
> in-place copy construction or even better using in-place factories.
>
> We do not even need to explicitly store the size if we take  
> advantage of uninitialized and initialized elements, just like how  
> modern implementations of std::vector do.
>
> Another minor thing is to apply the empty member/base optimizations  
> (EMO/EBO) for allocator types which are empty in size.
>
> So i would like to know the rationale for these, since i need  
> something like multi_array i may just make the adjustments myself.
>
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