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# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
from __future__ import absolute_import, division, print_function
import construct
import six
class _UBInt24(construct.Adapter):
def _encode(self, obj, context):
return (
six.int2byte((obj & 0xFF0000) >> 16) +
six.int2byte((obj & 0x00FF00) >> 8) +
six.int2byte(obj & 0x0000FF)
)
def _decode(self, obj, context):
obj = bytearray(obj)
return (obj[0] << 16 | obj[1] << 8 | obj[2])
def UBInt24(name): # noqa
return _UBInt24(construct.Bytes(name, 3))
def LengthPrefixedArray(subcon, length_field=construct.UBInt8("length")):
"""
An array prefixed by a byte length field.
In contrast to construct.macros.PrefixedArray,
the length field signifies the number of bytes, not the number of elements.
"""
subcon_with_pos = construct.Struct(
subcon.name,
construct.Embed(subcon),
construct.Anchor("__current_pos")
)
return construct.Embed(
construct.Struct(
"",
length_field,
construct.Anchor("__start_pos"),
construct.RepeatUntil(
lambda obj, ctx: obj.__current_pos == ctx.__start_pos + getattr(ctx, length_field.name),
subcon_with_pos
),
)
)
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