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// Copyright 2020 The Pigweed Authors
// 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
// 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.
// Provides an implementation of the CCITT CRC16 for the polynomial
// x^16 + x^12 + x^5 + 1
// Polynomial 0x1021, initial value 0xFFFF. See
#pragma once
#include <stddef.h>
#include <stdint.h>
#ifdef __cplusplus
extern "C" {
#endif // __cplusplus
// C API for calculating the CCITT CRC16 of an array of data.
uint16_t pw_ChecksumCcittCrc16(const void* data,
size_t size_bytes,
uint16_t initial_value);
#ifdef __cplusplus
} // extern "C"
#include "pw_span/span.h"
namespace pw::checksum {
inline constexpr uint16_t kCcittCrc16DefaultInitialValue = 0xFFFF;
// Calculates the CCITT CRC16 for the provided data. To update an existing CRC,
// pass the previous value as the initial_value argument.
inline uint16_t CcittCrc16(
span<const std::byte> data,
uint16_t initial_value = kCcittCrc16DefaultInitialValue) {
return pw_ChecksumCcittCrc16(, data.size_bytes(), initial_value);
// Calculates the CCITT CRC16 for a single byte. This is useful for updating a
// CRC byte-by-byte.
inline uint16_t CcittCrc16(
std::byte value, uint16_t initial_value = kCcittCrc16DefaultInitialValue) {
return pw_ChecksumCcittCrc16(&value, sizeof(value), initial_value);
} // namespace pw::checksum
#endif // __cplusplus