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