SQL> set list on;
SQL> set term ^;
SQL> execute block returns( ip_a varchar(21), ip_b varchar(21) ) as
CON>     declare function fn_internal_ip_address() returns varchar(21) deterministic
CON>         as begin
CON>             rdb$get_context('SYSTEM', 'CLIENT_ADDRESS');
CON>         end
CON> begin
CON>    ip_a = fn_internal_ip_address(); 
CON>   ip_b = rdb$get_context('SYSTEM', 'CLIENT_ADDRESS');
CON>   suspend;
CON> end^

IP_A                             <null> 
IP_B                            192.168.43.96

execute block returns( ip_a varchar(21), ip_b varchar(21), ssn int, trn int ) as
    declare function fn_internal_ip_address() returns varchar(21) deterministic
        as begin
            rdb$get_context('SYSTEM', 'CLIENT_ADDRESS');
        end
    declare function fn_internal_ssn() returns varchar(21) deterministic
        as begin
            return rdb$get_context('USER_SESSION', 'MY_SESSION');
        end
    declare function fn_internal_trn() returns varchar(21) deterministic
        as begin
            return rdb$get_context('USER_TRANSACTION', 'MY_TRANSACTION');
        end
begin
  rdb$set_context('USER_SESSION', 'MY_SESSION', current_connection);
  rdb$set_context('USER_TRANSACTION', 'MY_TRANSACTION', current_transaction);

  ip_a = fn_internal_ip_address();
  ip_b = rdb$get_context('SYSTEM', 'CLIENT_ADDRESS');

  ssn = fn_internal_ssn();
  trn = fn_internal_trn();

  suspend;
end

set term ^;
execute block returns(n int, elap int) as
  declare i int;
  declare q int;
  declare t timestamp;
  declare function fn_internal_determ() returns int deterministic as
  begin
    return rdb$get_context('SYSTEM', 'LOCK_TIMEOUT');
  end
  declare function fn_internal_common() returns int as
  begin
    return rdb$get_context('SYSTEM', 'LOCK_TIMEOUT');
  end
begin
  q=10000000;
  n=q;
  t='now';
  while(n>0) do begin
      -- время выполнения БЕЗ всяких вызовов: 2883 ms
      -- i=fn_internal_determ(); -- 1e7 ==> 3405 ms 
      --i=rdb$get_context('SYSTEM', 'LOCK_TIMEOUT'); -- 1e7 ==> 10418 ms
      --i=cast(rdb$get_context('SYSTEM', 'LOCK_TIMEOUT') as int); -- 1e7 ==> 11369 ms
      -- i=fn_internal_common(); -- 1e7 ==> 28088 ms 
      n=n-1;
  end
  elap=datediff(millisecond from t to cast('now' as timestamp));
  n=q;
  suspend;
end
^set term ;^