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""" Compact Int parsing / serialization """
import io
def to_bytes(i: int) -> bytes:
"""encodes an integer as a compact int"""
if i < 0:
raise ValueError("integer can't be negative: {}".format(i))
order = 0
while i >> (8 * (2**order)):
order += 1
if order == 0:
if i < 0xFD:
return bytes([i])
order = 1
if order > 3:
raise ValueError("integer too large: {}".format(i))
return bytes([0xFC + order]) + i.to_bytes(2**order, "little")
def from_bytes(b: bytes) -> int:
s = io.BytesIO(b)
res = read_from(s)
if len(s.read(1)) > 0:
raise ValueError("Too many bytes")
return res
def read_from(stream) -> int:
"""reads a compact integer from a stream"""
c = stream.read(1)
if not isinstance(c, bytes):
raise TypeError("Bytes must be returned from stream.read()")
if len(c) != 1:
raise RuntimeError("Can't read one byte from the stream")
i = c[0]
if i >= 0xFD:
bytes_to_read = 2 ** (i - 0xFC)
return int.from_bytes(stream.read(bytes_to_read), "little")
else:
return i
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