from typing import Iterable, List
from .constants import CHECKSUM_LENGTH_WORDS, CUSTOMIZATION_STRING
def _polymod(values: Iterable[int]) -> int:
GEN = (
0xE0E040,
0x1C1C080,
0x3838100,
0x7070200,
0xE0E0009,
0x1C0C2412,
0x38086C24,
0x3090FC48,
0x21B1F890,
0x3F3F120,
)
chk = 1
for v in values:
b = chk >> 20
chk = (chk & 0xFFFFF) << 10 ^ v
for i in range(10):
chk ^= GEN[i] if ((b >> i) & 1) else 0
return chk
def create_checksum(data: Iterable[int]) -> List[int]:
values = list(CUSTOMIZATION_STRING) + list(data) + [0] * CHECKSUM_LENGTH_WORDS
polymod = _polymod(values) ^ 1
return [(polymod >> 10 * i) & 1023 for i in reversed(range(CHECKSUM_LENGTH_WORDS))]
def verify_checksum(data: Iterable[int]) -> bool:
return _polymod(list(CUSTOMIZATION_STRING) + list(data)) == 1
