ab test

ab.java

	private static boolean isInAGroup(@Nonnull String sessionId, int base) {
		int sum = 0;
		for(int i : sessionId.toCharArray()) {
			sum += i;
		}
		sum = sum / base; // integer division is like Math.floor(sum / base)
		return sum % 2 == 0;
	}

ab.py

def is_in_a_group(username, base=1):
    """
    determines if user takes part in ab test

    :param username:    username of authenticated request
    :param base:        identifier of the ab group
    :return:            true if user is in a group
    """
    num = sum(bytearray(username, "UTF-8"))
    num = num // base
    num %= 2
    return num == 0

ab.sql

CREATE OR REPLACE FUNCTION in_a_group(username TEXT, base INT)
  RETURNS BOOL AS $$
DECLARE s INT := 0;
        c CHAR;
        t BOOL;
BEGIN
  FOREACH c IN ARRAY regexp_split_to_array(username, '')
  LOOP
    s := s + ascii(c);
  END LOOP;

  s := s / base;
  s := s % 2;

  t := s = 0;
  RETURN t;
END
$$
LANGUAGE plpgsql;

unit_test.py

usernames = ["daniel", "christoph", "tobias", "marius", "daniela", "barbara", "hans"]
for base in [1, 3]:
   print("\n# use base={} ...".format(base))
   for u in usernames:
     is_in = is_in_a_group(u, base)
     print("#   {}: {}".format(u, is_in))
    
# use base=1 ...
#   daniel: False
#   christoph: True
#   tobias: True
#   marius: False
#   daniela: True
#   barbara: False
#   hans: True

# use base=3 ...
#   daniel: False
#   christoph: True
#   tobias: True
#   marius: False
#   daniela: False
#   barbara: True
#   hans: True