Couldnt understand the code in chapter-2 while separating test set

Hi Mr.Aurélien Géron,

In your book while separating the test set you have written.
def test_set_check(identifier, test_ratio, hash):
return hash(np.int64(identifier)).digest()[-1] < 256 * test_ratio
def split_train_test_by_id(data, test_ratio, id_column, hash=hashlib.md5):
ids = data[id_column]
in_test_set = ids.apply(lambda id_: test_set_check(id_, test_ratio, hash))
return data.loc[~in_test_set], data.loc[in_test_set]

Can you help me to understand how hash helps in separating the test set and avoid the problems mentioned before. In the second book you have used crc32 and the code is as following:
from zlib import crc32
def test_set_check(identifier, test_ratio):
return crc32(np.int64(identifier)) & 0xffffffff < test_ratio * 2**32
How does this equals to the above code?