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

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #2703: lagged_fibonacci_01::seed() bug
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-02-01 15:48:00

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

Comment(by rick68_at_[hidden]):

 Hi,

 In <boost/random/subtract_with_carry.hpp>, I found member fucntion
 substract_with_carry::seed(), it is similar lagged_fibonacci_01::seed().

 line295:  template<class It>[[BR]]
 line296:  void seed(It& first, It last)[[BR]]
 line297:  {[[BR]]
 line298:#ifndef BOOST_NO_STDC_NAMESPACE[[BR]]
 line299:    // allow for Koenig lookup[[BR]]
 line300:    using std::fmod;[[BR]]
 line301:    using std::pow;[[BR]]
 line302:#endif[[BR]]
 line303:    unsigned long mask = ~((~0u) << (w%32));   // now lowest
 (w%32) bits set[[BR]]
 line304:    RealType two32 = pow(RealType(2), 32);[[BR]]
 line305:    unsigned int j;[[BR]]
 line306:    for(j = 0; j < long_lag && first != last; ++j) {[[BR]]
 line307:      x[j] = RealType(0);[[BR]]
 line308:      for(int i = 0; i < w/32 && first != last; ++i,
 ++first)[[BR]]
 line309:        x[j] += *first / pow(two32,i+1);[[BR]]
 line310:      if(first != last && mask != 0) {[[BR]]
 line311:        x[j] += fmod((*first & mask) / _modulus,
 RealType(1));[[BR]]
 line312:        ++first;[[BR]]
 line313:      }[[BR]]
 line314:    }[[BR]]
 line315:    if(first == last && j < long_lag)[[BR]]
 line316:      throw
 std::invalid_argument("subtract_with_carry_01::seed");[[BR]]
 line317:    carry = (x[long_lag-1] ? 0 : 1 / _modulus);[[BR]]
 line318:    k = 0;[[BR]]
 line319:  }[[BR]]

 Maybe lagged_fibonacci_01::seed() has mistake.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/2703#comment:3>
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