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Date: Fri, 7 Sep 2007 18:04:31 -0700 (PDT)
From: "Travis Vitek (JIRA)" <jira@apache.org>
To: stdcxx-dev@incubator.apache.org
Subject: [jira] Updated: (STDCXX-493) std::string::append() slow
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     [ https://issues.apache.org/jira/browse/STDCXX-493?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Travis Vitek updated STDCXX-493:
--------------------------------

    Attachment: stdcxx-493.patch

Yes, I believe that this patch is good. It doesn't cause any regressions, and the performance is significantly improved for one of the cases in the test [op == 1]. I see similar results on windows. I'm attaching an updated patch that can be applied more easily.

2007-09-07  Mark Brown <mbrown@inbox.com>

	STDCXX-493
	string (append): replace calls to replace with calls
	to append to improve performance.

> std::string::append() slow
> --------------------------
>
>                 Key: STDCXX-493
>                 URL: https://issues.apache.org/jira/browse/STDCXX-493
>             Project: C++ Standard Library
>          Issue Type: Bug
>          Components: 21. Strings
>    Affects Versions: 4.1.3
>         Environment: gcc 4.1.2 on Linux/x86_64
>            Reporter: Mark Brown
>            Assignee: Travis Vitek
>             Fix For: 4.2
>
>         Attachments: stdcxx-493.patch
>
>
> This is a similar problem to STDCXX-492: all overloads of string::append() are slower than the same overloads in gcc:
> $ let n=0; while [ $n -lt 3 ]; do time LD_LIBRARY_PATH=../lib ./append-stdcxx-4.1.3 500000000 $n; let n=`expr $n + 1`; done
> real    0m11.221s
> user    0m9.941s
> sys     0m1.104s
> real    0m13.065s
> user    0m11.661s
> sys     0m1.236s
> real    0m7.837s
> user    0m6.660s
> sys     0m1.160s
> $ let n=0; while [ $n -lt 3 ]; do time ./append-gcc-4.1.2 500000000 $n; let n=`expr $n + 1`; done
> real    0m4.865s
> user    0m4.172s
> sys     0m0.692s
> real    0m7.617s
> user    0m6.920s
> sys     0m0.696s
> real    0m5.787s
> user    0m5.068s
> sys     0m0.720s
> The program I used to do the comaprison is below:
> #include <cassert>
> #include <cstdlib>
> #include <string>
> int main (int argc, char *argv[])
> {
>     const int N = argc < 2 ? 1 : std::atoi (argv [1]);
>     const int op = argc < 3 ? 0 : std::atoi (argv [2]);
>     std::string str;
>     const std::string x ("X");
>     if (op == 0) {
>         for (int i = 0; i < N; ++i)
>             str.append (1, 'x');
>     } else if (op == 1) {
>         for (int i = 0; i < N; ++i)
>             str.append ("x");
>     } else {
>         for (int i = 0; i < N; ++i)
>             str.append (x);
>     }
>     assert (str.size () == std::size_t (N));
> }

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