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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.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
{...}
peerplays/libraries/chain/include/graphene/chain/database.hpp
fc::hash_ctr_rng<secret_hash_type, 20> _random_number_generator;
peerplays/libraries/chain/db_management.cpp
_random_number_generator(fc::ripemd160().data())
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());
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;
}
}