94 lines
3.0 KiB
C++
94 lines
3.0 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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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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*/
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#pragma once
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#include <stdint.h>
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#include <cstddef>
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/*
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* Checksum functions
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*/
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namespace folly {
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/**
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* Compute the CRC-32C checksum of a buffer, using a hardware-accelerated
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* implementation if available or a portable software implementation as
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* a default.
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*
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* @note CRC-32C is different from CRC-32; CRC-32C starts with a different
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* polynomial and thus yields different results for the same input
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* than a traditional CRC-32.
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*/
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uint32_t
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crc32c(const uint8_t* data, size_t nbytes, uint32_t startingChecksum = ~0U);
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/**
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* Compute the CRC-32 checksum of a buffer, using a hardware-accelerated
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* implementation if available or a portable software implementation as
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* a default.
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*/
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uint32_t
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crc32(const uint8_t* data, size_t nbytes, uint32_t startingChecksum = ~0U);
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/**
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* Compute the CRC-32 checksum of a buffer, using a hardware-accelerated
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* implementation if available or a portable software implementation as
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* a default.
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*
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* @note compared to crc32(), crc32_type() uses a different set of default
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* parameters to match the results returned by boost::crc_32_type and
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* php's built-in crc32 implementation
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*/
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uint32_t
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crc32_type(const uint8_t* data, size_t nbytes, uint32_t startingChecksum = ~0U);
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/**
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* Given two checksums, combine them in to one checksum.
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*
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* Example:
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* len1 len2
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* Given a buffer [ checksum 1 | checksum 2 ]
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* such that the first buffer's crc is checksum1 and has length len1,
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* and the remainder of the buffer's crc is checksum2 and len 2,
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* a total checksum over the whole buffer can be made by:
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*
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* crc32_combine(checksum1, checksum 2, len2); // len1 not needed.
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*
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* Note that this is equivalent to:
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*
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* crc32(buffer2, len2, crc32(buffer1, len1));
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*
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* However, this allows calculating the checksums in parallel
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* or calculating checksum 2 before checksum 1.
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*
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* Additionally, this is also equivalent, but much slower:
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* crc2 = crc32(buffer2, len2, 0);
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* crc1 = crc32(buffer1, len1, 0);
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* combined = crc2 ^ crc32(buffer_of_all_zeros, len2, crc1);
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*
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* crc32[c]_combine is roughly ~10x faster than either of the other
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* above two examples.
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*/
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uint32_t crc32_combine(uint32_t crc1, uint32_t crc2, size_t crc2len);
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/* crc32c_combine is the same as crc32_combine, but uses the crc32c
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polynomial */
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uint32_t crc32c_combine(uint32_t crc1, uint32_t crc2, size_t crc2len);
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} // namespace folly
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