Alexander Nasonov's shared items

Saturday, August 26, 2006

[boost] [lexical_cast] optimization commited to HEAD

I just posted it to boost-devel list: Hello, I recently commited the version 1.26 of lexical_cast.hpp that optimizes many combinations of types. How it works: The lexical_cast reserves a local buffer for bool, char, wchar_t and other integral types. Then it puts a string representation of a source to the buffer. Currently, all such algorithms don't use ostream at all but it's easy to implement a generic algorithm that sets a put area of a ostream object to point to that buffer and puts a string representation to the buffer. When a source type is a pointer to char/wchar_t array or basic_string<>, its value is already a string representation of itself and a call to ostream output operator is omitted. Futher optimization is applied when a target type is either char/wchar_t or basic_string<>. In this case, std streams are not involved in a conversion at all. For all other target types, basic_istream object is contructed, its get area is set to a string representation of a source type and the operator>> is called. Optimization for the following source types is ON: bool char wchar_t other integral types char*, char const*, char[], char const[] wchar_t*, wchar_t const*, wchar_t[], wchar_t const[] std::basic_string<> Optimization for the following source types is OFF: enums float double signed char unsigned char signed char*, signed char const*, signed char[], signed char const[] unsigned char*, unsigned char const*, unsigned char[], unsigned char const[] all other types not listed in ON list Tested on VC6, VC7.1, VC8, gcc 3.4 and Borland 5.5. I couldn't run the test on Borland so I tested only that it compiles. Diff: cvs diff -r 1.24 -r 1.26 boost/lexical_cast.hpp Performance: Compiled with gcc 3.4.4 on FreeBSD 6.1 with -O2 flag turned on. A coversion from an int value [0, 9] to char. With Boost 1.33.1 - 2.012 s With Boost HEAD - 0.322 s, 6.24 times faster Ignore locales - 0.083 s A coversion from an int value [0, 999999] to std::string. With Boost 1.33.1 - 2.516 s With Boost HEAD - 0.844 s, 2.98 times faster Ignore locales - 0.626 s TODO - Optimization for float and double. - Make MEASURE_LEXICAL_CAST_PERFORMANCE_WITHOUT_LOCALE_OVERHEAD a public configuration parameter. - Discuss a behavior of enums with user-defined output operator.


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  2. Strange that I didn't receive any notification about your reply, Pavel.