[Boost-bugs] [Boost C++ Libraries] #2703: lagged_fibonacci_01::seed() bug

Subject: [Boost-bugs] [Boost C++ Libraries] #2703: lagged_fibonacci_01::seed() bug
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-01-31 14:28:05

#2703: lagged_fibonacci_01::seed() bug
------------------------------+---------------------------------------------
 Reporter:  rick68_at_[hidden]  |       Owner:  no-maintainer
     Type:  Bugs              |      Status:  new          
Milestone:  Boost 1.38.0      |   Component:  random       
  Version:  Boost 1.37.0      |    Severity:  Problem      
 Keywords:                    |  
------------------------------+---------------------------------------------
 Hi,

 In <boost/random/lagged_fibonacci_01.hpp>

 line309:  template<class It>[[BR]]
 line310:  void seed(It& first, It last)[[BR]]
 line311:  {[[BR]]
 line312:#ifndef BOOST_NO_STDC_NAMESPACE[[BR]]
 line313:    // allow for Koenig lookup[[BR]]
 line314:    using std::fmod;[[BR]]
 line315:    using std::pow;[[BR]]
 line316:#endif[[BR]]
 line317:    unsigned long mask = ~((~0u) << (w%32));   // now lowest w
 bits set[[BR]]
 line318:    RealType two32 = pow(RealType(2), 32);[[BR]]
 line319:    unsigned int j;[[BR]]
 line320:    for(j = 0; j < long_lag && first != last; ++j, ++first)
 {[[BR]]
 line312:      x[j] = RealType(0);[[BR]]
 line313:      for(int k = 0; k < w/32 && first != last; ++k,
 ++first)[[BR]]
 line314:        x[j] += *first / pow(two32,k+1);[[BR]]
 line315:      if(first != last && mask != 0)[[BR]]
 line316:        x[j] += fmod((*first & mask) / _modulus,
 RealType(1));[[BR]]
 line317:    }[[BR]]
 line318:    i = long_lag;[[BR]]
 line319:    if(first == last && j < long_lag)[[BR]]
 line320:      throw
 std::invalid_argument("lagged_fibonacci_01::seed");[[BR]]
 line321:  }[[BR]]

 line 313 maybe rewrite to:

       for(int k = 0; k < w/32 && first != last; ++k)

 because of the first "for loop" can't be broken.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/2703>
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