[Boost-bugs] [Boost C++ Libraries] #5158: [pending] speed up lowest_bit() for gcc 4.x compatibles

Subject: [Boost-bugs] [Boost C++ Libraries] #5158: [pending] speed up lowest_bit() for gcc 4.x compatibles
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-02-04 00:36:32

#5158: [pending] speed up lowest_bit() for gcc 4.x compatibles
-------------------------------------+--------------------------------------
 Reporter:  astukalov@…              |       Owner:  dlwalker    
     Type:  Patches                  |      Status:  new         
Milestone:  To Be Determined         |   Component:  integer     
  Version:  Boost Development Trunk  |    Severity:  Optimization
 Keywords:                           |  
-------------------------------------+--------------------------------------
 The patch provides specialization of lowest_bit() template that utilizes
 __builtin_ctz[l][l]() function, available for gcc 4.x-compatible
 compilers, instead of calculation-intensive path that makes use of
 integer_log2().

 Since lowest_bit() is used in dynamic_bitset::find_first()/find_next(),
 the patch leads to significant speed up for bitset traversal.

 The patch was tested on gcc 4.5.2 x86_64 and icc 11.1 x86_64.

 Currently, the patch provides no checks, if __builting_ctz is available
 for current toolset. I can try to add this, given the overall positive
 feedback.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5158>
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