Tackling library IO performance

[Paolo Carlini]

Jerry Quinn wrote:

>Next, I tried to bypass the call to grouping() in
>num_put<char>::_M_widen_int.  It turns out that the virtual call to
>numpunct<char>::grouping() is expensive.  Bypassing this call brings
>the runtime from 22s down to 11s!
>
>After some digging in the archives, I found that Nathan Myers
>originally added a mechanism to deal with this by caching some of the
>formatting strings, paying for the virtual calls once per locale.
>However, the format cache was removed in
>http://gcc.gnu.org/ml/libstdc++/2001-11/msg00279.html.  But I couldn't
>find a reason for the removal of the cache.  My suspicion is that it
>is tied to threading issues, but I don't know.
>
>I added the old format cache back in to my test program and got about
>the same runtime improvement.
>
Hi Jerry. I like in particular this part of your work, which is generic
(not tied to a particular type) and promise to bring a substantive
improvement.

Thanks in advance for your contributions!

Paolo.