Some Source Engine RNG shit

// Here's some functions from Source Engine that synchronize RNG between client and server. This of course will have to be implemented differently in Zandronum, but it should perhaps give you guys some ideas on how to do it conceptually.

void CBaseEntity::SetPredictionRandomSeed( const CUserCmd *cmd ) // CBaseEntity is the base class for every entity. This means enemies, players, and everything alike.
{                                                                // CUserCmd is basically the current command being executed by the player/entity. Pretty sure Zan has an analogue.
    if ( !cmd )
    {
        m_nPredictionRandomSeed = -1;
#ifdef SERVER_DLL
        m_nPredictionRandomSeedServer = -1;
#endif

        return;
    }

    m_nPredictionRandomSeed = ( cmd->random_seed );
#ifdef SERVER_DLL
    m_nPredictionRandomSeedServer = ( cmd->server_random_seed );
#endif
}

inline int CBaseEntity::GetPredictionRandomSeed( bool bUseUnSyncedServerPlatTime ) // The bool here determines whether or not we're using the unsynched server seed, or the client/server synched seed.
{
#ifdef SERVER_DLL
    return bUseUnSyncedServerPlatTime ? m_nPredictionRandomSeedServer : m_nPredictionRandomSeed;
#else
    return m_nPredictionRandomSeed;
#endif
}

ConVar sv_usercmd_custom_random_seed( "sv_usercmd_custom_random_seed", "1", FCVAR_CHEAT, "When enabled server will populate an additional random seed independent of the client" );

void CBasePlayer::ProcessUsercmds( CUserCmd *cmds, int numcmds, int totalcmds, int dropped_packets, bool paused ) // CBasePlayer is the base player pawn class, inherits from CBaseEntity. This is where the player's user commands (button presses, etc) are processed.
{
//*snip*

                if ( sv_usercmd_custom_random_seed.GetBool() ) // Refer to the cvar description above.
        {
            float fltTimeNow = float( Plat_FloatTime() * 1000.0 ); // Based on current platform time.
            pCmd->server_random_seed = *reinterpret_cast<int*>( (char*)&fltTimeNow );
        }
        else
        {
            pCmd->server_random_seed = pCmd->random_seed; // just copy the current synched RNG from CUserCmd.
        }
}

class CUserCmd // Base class for user commands
{
//*snip*

    int     random_seed;    // For shared random functions
#ifdef SERVER_DLL
    int     server_random_seed; // Only the server populates this seed
#endif
}

void ReadUsercmd( bf_read *buf, CUserCmd *move, CUserCmd *from ) // function that reads user commands that have been recieved on client and server alike, for entities and players.
{
  //*snip*

  move->random_seed = MD5_PseudoRandom( move->command_number ) & 0x7fffffff;
}

// Now, here's an example of it's use in a function:
void CBaseEntity::FireBullets( const FireBulletsInfo_t &info )
{
    //*snip*

        // Hitscan Prediction is only usable on players
    int iSeed = 0;
    if ( IsPlayer() )
    {
        iSeed = CBaseEntity::GetPredictionRandomSeed( info.m_bUseServerRandomSeed ) & 255;
    }

//*snip*

        for (int iShot = 0; iShot < info.m_iShots; iShot++) // Use your imagination here, such as like for each pellet of a A_FireBullets shot.
    {
        //*snip*
        // Prediction is only usable on players
        if ( IsPlayer() )
        {
            RandomSeed( iSeed );    // init random system with this seed
        }

                // Get numbers from RNG, Trace an attack, etc...
        }
}