A couple of numbers (Re: [patch/rfa] Tiny but delicate...)

[Paolo Carlini <pcarlini at suse dot de>]

Paolo Carlini wrote:

> ..... If the idea works we
> obtain, not only a slightly simpler _M_mutate, but, more importantly,
> we keep on using the empty_rep trick even after things like
>
>    string str;
>    str.append(0, 'x');
>
> which currently leads to normal dynamically allocated memory.

A tiny test to give you an order of magnitude of the improvement
(actually, this is for the further tweaked version of the patch):


 for (unsigned i = 0; i < 10000000; ++i)
   {
     std::string a;
     a.append(0, 'x');
   }


current
-------
2.530u 0.000s 0:02.53 100.0%    0+0k 0+0io 168pf+0w

patched
-------
0.500u 0.000s 0:00.50 100.0%    0+0k 0+0io 157pf+0w


Paolo.