RNG API

Get a random number
Function uint64_t database::get_random_bits(uint64_t bound)
Parameters
Returns
bound: The upper limit for the random number.
A random number within the bound range.
TypeDefs
peerplays/libraries/chain/include/graphene/chain/protocol/types.hpp
typedef fc::ripemd160 secret_hash_type;
​
​
peerplays/libraries/fc/include/fc/crypto/hash_ctr_rng.hpp
template<class HashClass, int SeedLength>
​
class hash_ctr_rng
{...}
Declaration
peerplays/libraries/chain/include/graphene/chain/database.hpp 
​
fc::hash_ctr_rng<secret_hash_type, 20> _random_number_generator;
Examples
Initialization in constructor
peerplays/libraries/chain/db_management.cpp
​
_random_number_generator(fc::ripemd160().data())
Updating seed on a new block
peerplays/libraries/chain/db_update.cpp
​
modify( _dgp, [&]( dynamic_global_property_object& dgp ){
      secret_hash_type::encoder enc;       
      fc::raw::pack( enc, dgp.random );       
      fc::raw::pack( enc, b.previous_secret );        
      dgp.random = enc.result();
      _random_number_generator = fc::hash_ctr_rng<secret_hash_type, 20>(dgp.random.data());
Getting a new random number
peerplays/libraries/chain/db_update.cpp
​
uint64_t database::get_random_bits( uint64_t bound )
{
   return _random_number_generator(bound);
}
​
peerplays/libraries/fc/include/fc/crypto/hash_ctr_rng.hpp
​
      uint64_t operator()( uint64_t bound )
      {
         if( bound <= 1 )
            return 0;
         uint8_t bitcount = boost::multiprecision::detail::find_msb( bound ) + 1;
         // probability of loop exiting is >= 1/2, so probability of
         // running N times is bounded above by (1/2)^N
         while( true )
         {
            uint64_t result = get_bits( bitcount );
            if( result < bound )
               return result;
         }
      }