[PATCH] Optimize __convert_from_v when locale is already set

[Brad Spencer <spencer at infointeractive dot com>]

While debugging recently, I noticed that every time __convert_from_v
is called, there are expensive calls to malloc, free, strlen, strcpy,
and two possibly unnecessary extra calls to setlocale.  I've added a
cheap check to see if the locale is already "C" before we get out the
hammers.  I haven't address the exception safety issues raised
earlier.

I used a simple test to see if it is actually faster:

#include <iostream>

using std::cout;

int
main()
{
  const int x = 12345;

  for(unsigned int i = 0; i < 1000000; ++i) {
    cout << x;
  }

  return 0;
}

$ locale
LANG=C
LC_CTYPE="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_COLLATE="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_PAPER="C"
LC_NAME="C"
LC_ADDRESS="C"
LC_TELEPHONE="C"
LC_MEASUREMENT="C"
LC_IDENTIFICATION="C"
LC_ALL=

$ test-gcc/i686-pc-linux-gnu/bin/g++ -Wall -g -O6 -o loc main.cc
$ time ./loc >/dev/null

real    0m3.066s
user    0m3.070s
sys     0m0.000s

$ g++ -Wall -g -O6 -o loc-stock main.cc
$ time ./loc-stock >/dev/null

real    0m3.416s
user    0m3.410s
sys     0m0.000s

This seems to be harmless... Is it not?  I couldn't seem to set my
locale (inside the application) no matter what I tried, so I haven't 
tested opposite case to see how much it slows down (if it is at all
noticable). 

I'm also curious as to whether the entire locale needs to be changed.
I take it that the character set is what is preventing just LC_NUMERIC
from being modified?  Or am I just naive? :)

Patch attached.
        
-- 
------------------------------------------------------------------
Brad Spencer - spencer@infointeractive.com - "It's quite nice..."
Systems Architect | InfoInterActive Corp. | A Canadian AOL Company

Attachment: gcc-3.2-libstdc++-v3-locale_facets-optimized.patch
Description: Text document