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Date: Mon, 24 Sep 2007 14:16:51 -0700 (PDT)
From: "Travis Vitek (JIRA)" <jira@apache.org>
To: stdcxx-dev@incubator.apache.org
Subject: [jira] Updated: (STDCXX-492) std::string::operator+=() slow
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     [ https://issues.apache.org/jira/browse/STDCXX-492?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Travis Vitek updated STDCXX-492:
--------------------------------

    Attachment: string.patch

Patch improves times of both basic_string<>::append() and basic_string<>::op+=().

I've looked at the gnu changelog format description, and it doesn't mention what to do when you are changing multiple overloads of the same functions. I'm guessing, here, but if that is wrong, please correct me.


2007-09-24  Travis Vitek  <vitek@roguewave.com>

	STDCXX-492
	* string (operator+=): replace call to append with push_back
	for performance.
	(append): avoid calling replace() from append if there is
	sufficient buffer space available for performance.
	(append): simplify append overload, move it to header and then
	inline it.
	(append): use _RWSTD_SIZE_T to avoid integer overflow problems
	that could lead to heap	corruption.
	(push_back): call replace() instead of append when buffer
	reallocation required. cleanup. avoid integer overflow problem.
	* string.cc (append): moved append overload to header and make
	it inline.


> std::string::operator+=() slow
> ------------------------------
>
>                 Key: STDCXX-492
>                 URL: https://issues.apache.org/jira/browse/STDCXX-492
>             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: string.patch
>
>
> Comparing overloads of string::operator+=() in stdcxx with the same functions in gcc 4.1.2, stdcxx is up to twice slower than gcc:
> $ time ./op_plus_equal-stdcxx 100000000 0
> real    0m2.241s
> user    0m1.932s
> sys     0m0.204s
> $ time ./op_plus_equal-stdcxx 100000000 1
> real    0m2.540s
> user    0m2.344s
> sys     0m0.196s
> $ time ./op_plus_equal-stdcxx 100000000 2
> real    0m1.492s
> user    0m1.308s
> sys     0m0.184s
> $ time ./op_plus_equal-gcc 100000000 0
> real    0m0.883s
> user    0m0.728s
> sys     0m0.156s
> $ time ./op_plus_equal-gcc 100000000 1
> real    0m1.589s
> user    0m1.424s
> sys     0m0.168s
> $ time ./op_plus_equal-gcc 100000000 2
> real    0m1.131s
> user    0m0.976s
> sys     0m0.156s
> #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 += 'x';
>     } else if (op == 1) {
>         for (int i = 0; i < N; ++i)
>             str += "x";
>     } else {
>         for (int i = 0; i < N; ++i)
>             str += x;
>     }
>     assert (str.size () == std::size_t (N));
> }

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