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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from __future__ import absolute_import, division, print_function
import six
def _truncate_digest(digest, order_bits):
digest_len = len(digest)
if 8 * digest_len > order_bits:
digest_len = (order_bits + 7) // 8
digest = digest[:digest_len]
if 8 * digest_len > order_bits:
rshift = 8 - (order_bits & 0x7)
assert rshift > 0 and rshift < 8
mask = 0xFF >> rshift << rshift
# Set the bottom rshift bits to 0
digest = digest[:-1] + six.int2byte(six.indexbytes(digest, -1) & mask)
return digest
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