49 lines
1.5 KiB
Python
49 lines
1.5 KiB
Python
from typing import Dict
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# Таблица Base64-подобного варианта
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VariantBase64Table: str = (
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"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
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)
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VariantBase64Dict: Dict[int, str] = {
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i: VariantBase64Table[i] for i in range(len(VariantBase64Table))
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}
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VariantBase64ReverseDict: Dict[str, int] = {
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VariantBase64Table[i]: i for i in range(len(VariantBase64Table))
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}
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def variant_base64_encode(bs: bytes) -> bytes:
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"""
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Пользовательский Base64 encode (малые блоки, little-endian).
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Аргументы:
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- bs: bytes - исходные данные
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Возвращает:
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- bytes: закодированные данные
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"""
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result: bytearray = bytearray()
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blocks_count, left_bytes = divmod(len(bs), 3)
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# Полные блоки по 3 байта
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for i in range(blocks_count):
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b: bytes = bs[3*i:3*i+3]
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coding_int: int = int.from_bytes(b, "little")
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block: str = "".join(
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VariantBase64Dict[(coding_int >> shift) & 0x3F]
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for shift in (0, 6, 12, 18)
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)
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result.extend(block.encode("ascii"))
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# Обработка оставшихся байт
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if left_bytes:
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b: bytes = bs[-left_bytes:]
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coding_int: int = int.from_bytes(b, "little")
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block: str = "".join(
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VariantBase64Dict[(coding_int >> shift) & 0x3F]
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for shift in range(0, left_bytes * 8 + 1, 6)
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)
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result.extend(block.encode("ascii"))
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return bytes(result)
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