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[Patch] Speed up operator>>(istream, string)
- From: Paolo Carlini <pcarlini at suse dot de>
- To: libstdc++ <libstdc++ at gcc dot gnu dot org>
- Date: Thu, 20 May 2004 12:03:34 +0200
- Subject: [Patch] Speed up operator>>(istream, string)
Hi,
the below consistently improves operator>>(..., string) in the same way of
getline(..., string).
For a testcase identical to streams.cpp in 15002, besides 'f >> l' instead
of 'getline(f, l)', these are some numbers on my usual machine (on x86_64
the results are similar):
3.4.0
-----
9.090u 0.080s 0:09.22 99.4% 0+0k 0+0io 206pf+0w
3.4.1 pre
---------
3.470u 0.140s 0:03.81 94.7% 0+0k 0+0io 204pf+0w
3.4.1 pre + patch
-----------------
1.400u 0.110s 0:01.51 100.0% 0+0k 0+0io 205pf+0w
3.5 exp
-------
7.050u 0.090s 0:07.18 99.4% 0+0k 0+0io 208pf+0w
3.5 exp + patch
---------------
1.500u 0.080s 0:01.58 100.0% 0+0k 0+0io 209pf+0w
Icc8.0
------
2.770u 0.110s 0:02.89 99.6% 0+0k 0+0io 203pf+0w
As you can see, the code generated by unpatched mainline is not as good
as 3_4-branch: sadly, I'm seeing this rather often, for other performance
testcases in the iostreams area too.
Anyway, of course the patch would go in mainline only, for now, and I'm
also adding a couple of new testcases.
A will wait a few hours, in case of comments.
Regtested x86-linux.
Paolo.
///////////////
2004-05-20 Paolo Carlini <pcarlini@suse.de>
* include/bits/istream.tcc (operator>>(basic_istream<>&,
basic_string<>&)): Use a temporary buffer, thus avoiding
reallocation for common case.
* testsuite/21_strings/basic_string/inserters_extractors/char/11.cc:
New.
* testsuite/21_strings/basic_string/inserters_extractors/wchar_t/11.cc:
Likewise.
diff -urN libstdc++-v3-orig/include/bits/istream.tcc libstdc++-v3/include/bits/istream.tcc
--- libstdc++-v3-orig/include/bits/istream.tcc 2004-04-26 17:26:18.000000000 +0200
+++ libstdc++-v3/include/bits/istream.tcc 2004-05-20 10:50:40.000000000 +0200
@@ -1043,11 +1043,13 @@
{
try
{
+ // Avoid reallocation for common case.
__str.erase();
- streamsize __w = __in.width();
- __size_type __n;
- __n = __w > 0 ? static_cast<__size_type>(__w) : __str.max_size();
-
+ _CharT __buf[128];
+ __size_type __len = 0;
+ const streamsize __w = __in.width();
+ const __size_type __n = __w > 0 ? static_cast<__size_type>(__w)
+ : __str.max_size();
const __ctype_type& __ct = use_facet<__ctype_type>(__in.getloc());
const __int_type __eof = _Traits::eof();
__streambuf_type* __sb = __in.rdbuf();
@@ -1057,10 +1059,17 @@
&& !_Traits::eq_int_type(__c, __eof)
&& !__ct.is(ctype_base::space, _Traits::to_char_type(__c)))
{
- __str += _Traits::to_char_type(__c);
+ if (__len == sizeof(__buf) / sizeof(_CharT))
+ {
+ __str.append(__buf, sizeof(__buf) / sizeof(_CharT));
+ __len = 0;
+ }
+ __buf[__len++] = _Traits::to_char_type(__c);
++__extracted;
__c = __sb->snextc();
}
+ __str.append(__buf, __len);
+
if (_Traits::eq_int_type(__c, __eof))
__err |= ios_base::eofbit;
__in.width(0);
@@ -1102,7 +1111,7 @@
{
try
{
- // Avoid reallocation for common case.
+ // Avoid reallocation for common case.
__str.erase();
_CharT __buf[128];
__size_type __len = 0;
diff -urN libstdc++-v3-orig/testsuite/21_strings/basic_string/inserters_extractors/char/11.cc libstdc++-v3/testsuite/21_strings/basic_string/inserters_extractors/char/11.cc
--- libstdc++-v3-orig/testsuite/21_strings/basic_string/inserters_extractors/char/11.cc 1970-01-01 01:00:00.000000000 +0100
+++ libstdc++-v3/testsuite/21_strings/basic_string/inserters_extractors/char/11.cc 2004-05-20 11:11:37.000000000 +0200
@@ -0,0 +1,79 @@
+// Copyright (C) 2004 Free Software Foundation
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 2, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING. If not, write to the Free
+// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+// USA.
+
+// 21.3.7.9 inserters and extractors
+
+#include <istream>
+#include <string>
+#include <fstream>
+#include <testsuite_hooks.h>
+
+using namespace std;
+
+string prepare(string::size_type len, unsigned nchunks)
+{
+ string ret;
+ for (unsigned i = 0; i < nchunks; ++i)
+ {
+ for (string::size_type j = 0; j < len; ++j)
+ ret.push_back('a' + rand() % 26);
+ len *= 2;
+ ret.push_back(' ');
+ }
+ return ret;
+}
+
+void check(istream& stream, const string& str)
+{
+ bool test __attribute__((unused)) = true;
+
+ string chunk;
+ string::size_type index = 0, index_new = 0;
+
+ while (stream >> chunk)
+ {
+ index_new = str.find(' ', index);
+ VERIFY( !str.compare(index, index_new - index, chunk) );
+ index = index_new + 1;
+ }
+ VERIFY( stream.eof() );
+}
+
+// istream& operator>>(istream&, string&)
+void test01()
+{
+ const char filename[] = "inserters_extractors-3.txt";
+
+ const string data = prepare(666, 10);
+
+ ofstream ofstrm;
+ ofstrm.open(filename);
+ ofstrm.write(data.data(), data.size());
+ ofstrm.close();
+
+ ifstream ifstrm;
+ ifstrm.open(filename);
+ check(ifstrm, data);
+ ifstrm.close();
+}
+
+int main()
+{
+ test01();
+ return 0;
+}
diff -urN libstdc++-v3-orig/testsuite/21_strings/basic_string/inserters_extractors/wchar_t/11.cc libstdc++-v3/testsuite/21_strings/basic_string/inserters_extractors/wchar_t/11.cc
--- libstdc++-v3-orig/testsuite/21_strings/basic_string/inserters_extractors/wchar_t/11.cc 1970-01-01 01:00:00.000000000 +0100
+++ libstdc++-v3/testsuite/21_strings/basic_string/inserters_extractors/wchar_t/11.cc 2004-05-20 11:15:34.000000000 +0200
@@ -0,0 +1,79 @@
+// Copyright (C) 2004 Free Software Foundation
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 2, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING. If not, write to the Free
+// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+// USA.
+
+// 21.3.7.9 inserters and extractors
+
+#include <istream>
+#include <string>
+#include <fstream>
+#include <testsuite_hooks.h>
+
+using namespace std;
+
+wstring prepare(wstring::size_type len, unsigned nchunks)
+{
+ wstring ret;
+ for (unsigned i = 0; i < nchunks; ++i)
+ {
+ for (wstring::size_type j = 0; j < len; ++j)
+ ret.push_back(L'a' + rand() % 26);
+ len *= 2;
+ ret.push_back(L' ');
+ }
+ return ret;
+}
+
+void check(wistream& stream, const wstring& str)
+{
+ bool test __attribute__((unused)) = true;
+
+ wstring chunk;
+ wstring::size_type index = 0, index_new = 0;
+
+ while (stream >> chunk)
+ {
+ index_new = str.find(L' ', index);
+ VERIFY( !str.compare(index, index_new - index, chunk) );
+ index = index_new + 1;
+ }
+ VERIFY( stream.eof() );
+}
+
+// istream& operator>>(istream&, string&)
+void test01()
+{
+ const char filename[] = "inserters_extractors-3.txt";
+
+ const wstring data = prepare(666, 10);
+
+ wofstream ofstrm;
+ ofstrm.open(filename);
+ ofstrm.write(data.data(), data.size());
+ ofstrm.close();
+
+ wifstream ifstrm;
+ ifstrm.open(filename);
+ check(ifstrm, data);
+ ifstrm.close();
+}
+
+int main()
+{
+ test01();
+ return 0;
+}