def test_generate_exp_golomb_numbers_with_ascending_lengths(sign):
for length, number in islice(
generate_exp_golomb_with_ascending_lengths(sign),
128,
):
# Use a known-good implementation of a signed exp-golmb encoder and
# check length is correct.
f = BytesIO()
w = BitstreamWriter(f)
w.write_sint(number)
actual_length = to_bit_offset(*w.tell())
assert actual_length == length
# Check sign of number
if sign < 0:
assert number <= 0
else:
assert number >= 0
def test_happy_cases(self, block_bits, num_values, magnitude):
value_sets = {
dangle_type: generate_dangling_transform_values(
block_bits,
num_values,
dangle_type,
magnitude,
)
for dangle_type in DanglingTransformValueType
}
values_and_bits_beyond_ends = {}
for description, values in value_sets.items():
# Should all have required number of values
assert len(values) == num_values
# Should correctly encode into bounded block
f = BytesIO()
w = BitstreamWriter(f)
w.bounded_block_begin(block_bits)
for value in values:
w.write_sint(value)
# Should completely fill the block
length_used = to_bit_offset(*w.tell())
assert length_used == block_bits
# Check we actually wrote 'beyond' the end of the block
assert w.bits_remaining < 0
# Work out which value and which bits actually first crossed the
# end-of-block boundary (we'll later check that these actually
# match our expectations later)
w.flush()
f.seek(0)
r = BitstreamReader(f)
r.bounded_block_begin(block_bits)
value_beyond_end = None
bits_beyond_end = None
while r.bits_remaining >= 0:
value_beyond_end = r.read_sint()
bits_beyond_end = -r.bits_remaining
values_and_bits_beyond_ends[description] = (
value_beyond_end,
bits_beyond_end,
)
# Check that the dangling value dangles in the expected way
v, b = values_and_bits_beyond_ends[
DanglingTransformValueType.zero_dangling]
assert v == 0
assert b == 1
v, b = values_and_bits_beyond_ends[
DanglingTransformValueType.sign_dangling]
assert v != 0
assert (-v).bit_length() == magnitude
assert b == 1
v, b = values_and_bits_beyond_ends[
DanglingTransformValueType.stop_and_sign_dangling]
assert v != 0
assert (-v).bit_length() == magnitude
assert b == 2
v, b = values_and_bits_beyond_ends[
DanglingTransformValueType.lsb_stop_and_sign_dangling]
assert v != 0
# NB: Larger due to exp-golmb code needing to end in 1
assert (-v).bit_length() == magnitude + 1
assert b == 3