52 lines
1.6 KiB
Diff
52 lines
1.6 KiB
Diff
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the below is a (safe) backport from mainline and 3_4-branch: improves
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2-3x the performance of operator>>(basic_istream<>&, basic_string<>&),
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a rather common facility. Tested x86-linux, make check/check-abi.
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Paolo.
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///////////////
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[ Part 2: "Attached Text" ]
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2004-06-22 Paolo Carlini <pcarlini@suse.de>
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* include/bits/istream.tcc (operator>>(basic_istream<>&,
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basic_string<>&)): Use a temporary buffer, thus avoiding
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reallocation for common case.
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[ Part 3: "Attached Text" ]
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diff -urN libstdc++-v3-orig/include/bits/istream.tcc libstdc++-v3/include/bits/istream.tcc
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--- libstdc++-v3-orig/include/bits/istream.tcc 2004-05-02 18:10:34.000000000 +0200
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+++ libstdc++-v3/include/bits/istream.tcc 2004-06-22 14:22:07.000000000 +0200
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@@ -1038,7 +1038,10 @@
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{
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try
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{
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+ // Avoid reallocation for common case.
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__str.erase();
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+ _CharT __buf[128];
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+ __size_type __len = 0;
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streamsize __w = __in.width();
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__size_type __n;
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__n = __w > 0 ? static_cast<__size_type>(__w) : __str.max_size();
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@@ -1052,10 +1055,17 @@
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&& !_Traits::eq_int_type(__c, __eof)
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&& !__ct.is(ctype_base::space, _Traits::to_char_type(__c)))
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{
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- __str += _Traits::to_char_type(__c);
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+ if (__len == sizeof(__buf) / sizeof(_CharT))
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+ {
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+ __str.append(__buf, sizeof(__buf) / sizeof(_CharT));
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+ __len = 0;
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+ }
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+ __buf[__len++] = _Traits::to_char_type(__c);
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++__extracted;
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__c = __sb->snextc();
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}
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+ __str.append(__buf, __len);
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+
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if (_Traits::eq_int_type(__c, __eof))
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__err |= ios_base::eofbit;
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__in.width(0);
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