| // 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 |
| // |
| // https://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. |
| |
| // Provides an implementation of the CRC-16-CCITT or CRC-CCITT checksum, which |
| // uses the polynomial 0x1021: |
| // |
| // x^16 + x^12 + x^5 + 1 |
| // |
| // with initial value 0xFFFF. See https://www.zlib.net/crc_v3.txt. |
| #pragma once |
| |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| #ifdef __cplusplus |
| extern "C" { |
| #endif // __cplusplus |
| |
| // C API for calculating the CRC-16-CCITT of an array of data. |
| uint16_t pw_checksum_Crc16Ccitt(const void* data, |
| size_t size_bytes, |
| uint16_t initial_value); |
| |
| #ifdef __cplusplus |
| } // extern "C" |
| |
| #include <span> |
| |
| namespace pw::checksum { |
| |
| // Calculates the CRC-16-CCITT for all data passed to Update. |
| class Crc16Ccitt { |
| public: |
| static constexpr uint16_t kInitialValue = 0xFFFF; |
| |
| // Calculates the CRC-16-CCITT for the provided data and returns it as a |
| // uint16_t. To update a CRC in multiple calls, use an instance of the |
| // Crc16Ccitt class or pass the previous value as the initial_value argument. |
| static uint16_t Calculate(std::span<const std::byte> data, |
| uint16_t initial_value = kInitialValue) { |
| return pw_checksum_Crc16Ccitt( |
| data.data(), data.size_bytes(), initial_value); |
| } |
| |
| static uint16_t Calculate(std::byte data, |
| uint16_t initial_value = kInitialValue) { |
| return Calculate(std::span(&data, 1), initial_value); |
| } |
| |
| constexpr Crc16Ccitt() : value_(kInitialValue) {} |
| |
| void Update(std::span<const std::byte> data) { |
| value_ = Calculate(data, value_); |
| } |
| |
| void Update(std::byte data) { Update(std::span(&data, 1)); } |
| |
| // Returns the value of the CRC-16-CCITT for all data passed to Update. |
| uint16_t value() const { return value_; } |
| |
| // Resets the CRC to the initial value. |
| void clear() { value_ = kInitialValue; } |
| |
| private: |
| uint16_t value_; |
| }; |
| |
| } // namespace pw::checksum |
| |
| #endif // __cplusplus |