Patch for lexical_cast: additional optimizations

[Antony Polukhin <antoshkka@…>]

Patch to Boost Lexical Cast library, that returns Target directly constructed from Source in cases, when:
1) Source and Target are arithmetics (and not char or wchar_t), and all values of Source are in range of Target
2) Source and Target are both char or both wchar_t
3) Source is array of CharT and Target is std::basic_string<CharT, ...>
4) Source and Target are std::basic_string with same template parameters

It gives performance boost more than 10 times in case 1), about 7 times in case 2), and about 1.5 times in cases 3) and 4).

Existing tests for Boost Lexical Cast library cover considered cases. Patch was successfully tested on Intel 11.1.072, g++-4.4.5, VC++9 compilers.

It has the same behaviour, when casting out of bounds (int -> unsigned int, int -> short, unsigned int -> int). For checking bounds it uses boost::numeric::conversion_traits from <boost/numeric/conversion/conversion_traits.hpp>

Closes the ticket #4397

Was discussed at ​Boost mailing list

[Antony Polukhin <antoshkka@…>]

Patch for trunk version of lexical_cast (for revision 70337)

[Antony Polukhin]

(In [71958]) Fixes #5350. Fixes #4397 More tests (for conversions to float types, for conversions of negative values to unsigned integers)

When aws commiting to svn, supported the wrong number.

[anonymous]

More details at ​http://www.youtube.com/watch?v=XPpXll4GmwE