62 lines
2.0 KiB
Haskell
62 lines
2.0 KiB
Haskell
-- Copyright 2016 TensorFlow authors.
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--
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-- Licensed under the Apache License, Version 2.0 (the "License");
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-- you may not use this file except in compliance with the License.
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-- You may obtain a copy of the License at
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--
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-- http://www.apache.org/licenses/LICENSE-2.0
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--
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-- Unless required by applicable law or agreed to in writing, software
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-- distributed under the License is distributed on an "AS IS" BASIS,
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-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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-- See the License for the specific language governing permissions and
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-- limitations under the License.
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module TensorFlow.CRC32C
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( crc32c
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, crc32cLBS
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, crc32cUpdate
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, crc32cMasked
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, crc32cLBSMasked
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, crc32cMask
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, crc32cUnmask
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) where
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import Data.Bits (rotateL, rotateR)
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import qualified Data.ByteString as B
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import qualified Data.ByteString.Lazy as BL
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import Data.Digest.CRC32C (crc32c, crc32c_update)
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import Data.List (foldl')
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import Data.Word (Word32)
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-- | Compute the CRC32C checksum of the concatenation of the bytes checksummed
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-- by the given CRC32C value and the bytes in the given ByteString.
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crc32cUpdate :: Word32 -> B.ByteString -> Word32
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crc32cUpdate = crc32c_update
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-- | Compute the CRC32C checksum of the given bytes.
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crc32cLBS :: BL.ByteString -> Word32
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crc32cLBS = foldl' crc32cUpdate 0 . BL.toChunks
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-- | Scramble a CRC32C value so that the result can be safely stored in a
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-- bytestream that may itself be CRC'd.
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--
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-- This masking is the algorithm specified by TensorFlow's TFRecords format.
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crc32cMask :: Word32 -> Word32
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crc32cMask x = rotateR x 15 + maskDelta
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-- | Inverse of 'crc32cMask'.
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crc32cUnmask :: Word32 -> Word32
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crc32cUnmask x = rotateL (x - maskDelta) 15
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-- | Convenience function combining 'crc32c' and 'crc32cMask'.
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crc32cMasked :: B.ByteString -> Word32
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crc32cMasked = crc32cMask . crc32c
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-- | Convenience function combining 'crc32cLBS' and 'crc32cMask'.
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crc32cLBSMasked :: BL.ByteString -> Word32
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crc32cLBSMasked = crc32cMask . crc32cLBS
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maskDelta :: Word32
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maskDelta = 0xa282ead8
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