[boost] Re: Get/set state in Mersenne Twister

From: Neal Becker (ndbecker2_at_[hidden])
Date: 2004-09-01 21:27:37

Matthias Troyer wrote:

> On Sep 1, 2004, at 9:54 PM, Neal D. Becker wrote:
> 
>> In order to serialize, it would be helpful to add an interface to
>> mersenne_twister to get/set the state.  I don't think there is any I/F
>> to
>> get the state.
> 
> When we need to serialize RNGs we currently use the possibility to
> convert the state to a string using operator <<(std::ostream&, const
> RNG&)  and operator >>(std::istream&, RNG&). A better serialization
> mechanism should, in my opinion directly use the serialization library
> and not go over some get_state/set_state functions, since the state
> might be described by more than just a container.
> 

Maybe this is generic enough for any use?  It's not hard to make this work
for boost::python pickle:

*** mersenne_twister.hpp 2004-09-01 22:25:34.271533876 -0400
--- mersenne_twister.hpp.new 2004-09-01 22:10:43.674599123 -0400
***************
*** 133,138 ****
--- 133,147 ----
      return os;
    }
  
+   template<class Archive>
+   Archive&
+   getstate(Archive& ar) const
+   {
+     for(int j = 0; j < state_size; ++j)
+       ar << compute(j);
+     return ar;
+   }
+ 
    template<class CharT, class Traits>
    friend std::basic_istream<CharT,Traits>&
    operator>>(std::basic_istream<CharT,Traits>& is, mersenne_twister& mt)
***************
*** 145,150 ****
--- 154,172 ----
      mt.i = mt.state_size;
      return is;
    }
+ 
+   template<class Archive>
+   Archive&
+   setstate(Archive& ar)
+   {
+     for(int j = 0; j < state_size; ++j)
+       ar >> x[j];
+     // MSVC (up to 7.1) and Borland (up to 5.64) don't handle the template
+     // value parameter "n" available from the class template scope, so use
+     // the static constant with the same value
+     i = state_size;
+     return ar;
+   }
  #endif
  
    friend bool operator==(const mersenne_twister& x, const
mersenne_twister& y)