esp-idf/components/esp_rom/include/esp_rom_crc.h

// Copyright 2010-2020 Espressif Systems (Shanghai) PTE LTD
//
// 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

#ifdef __cplusplus
extern "C" {
#endif

#include <stdint.h>

/**           Notes about CRC API
 * The ESP32 ROM include some CRC tables and CRC APIs to speed up CRC calculation.
 * The CRC APIs include CRC8, CRC16, CRC32 algorithms for both little endian and big endian modes.
 * Here are the polynomials for the algorithms:
 * CRC-8        x8+x2+x1+1                                              0x07
 * CRC16-CCITT  x16+x12+x5+1                                            0x1021
 * CRC32        x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x1+1     0x04c11db7
 *
 * These group of CRC APIs are designed to calculate the data in buffers either continuous or not.
 * To make it easy, we had added a `~` at the beginning and the end of the functions.
 * To calculate non-continuous buffers, we can write the code like this:
 *     init = ~init;
 *     crc = crc32_le(init, buf0, length0);
 *     crc = crc32_le(crc, buf1, length1);
 *     crc = ~crc;
 *
 * However, it is not easy to select which API to use and give the correct parameters.
 * A specific CRC algorithm will include this parameters: width, polynomials, init, refin, refout, xorout
 *     refin and refout show the endian of the algorithm:
 *         if both of them are true, please use the little endian API.
 *         if both of them are false, please use the big endian API.
 *     xorout is the value which you need to be xored to the raw result.
 * However, these group of APIs need one '~' before and after the APIs.
 *
 * Here are some examples for CRC16:
 * CRC-16/CCITT, poly = 0x1021, init = 0x0000, refin = true, refout = true, xorout = 0x0000
 *     crc = ~crc16_le((uint16_t)~0x0000, buf, length);
 *
 * CRC-16/CCITT-FALSE, poly = 0x1021, init = 0xffff, refin = false, refout = false, xorout = 0x0000
 *     crc = ~crc16_be((uint16_t)~0xffff, buf, length);
 *
 * CRC-16/X25, poly = 0x1021, init = 0xffff, refin = true, refout = true, xorout = 0xffff
 *     crc = (~crc16_le((uint16_t)~(0xffff), buf, length))^0xffff;
 *
 * CRC-16/XMODEM, poly= 0x1021, init = 0x0000, refin = false, refout = false, xorout = 0x0000
 *     crc = ~crc16_be((uint16_t)~0x0000, buf, length);
 *
 */

/**
 * @brief CRC32 value in little endian.
 *
 * @param crc: Initial CRC value (result of last calculation or 0 for the first time)
 * @param buf: Data buffer that used to calculate the CRC value
 * @param len: Length of the data buffer
 * @return CRC32 value
 */
uint32_t esp_rom_crc32_le(uint32_t crc, uint8_t const *buf, uint32_t len);

/**
 * @brief CRC32 value in big endian.
 *
 * @param crc: Initial CRC value (result of last calculation or 0 for the first time)
 * @param buf: Data buffer that used to calculate the CRC value
 * @param len: Length of the data buffer
 * @return CRC32 value
 */
uint32_t esp_rom_crc32_be(uint32_t crc, uint8_t const *buf, uint32_t len);

/**
 * @brief CRC16 value in little endian.
 *
 * @param crc: Initial CRC value (result of last calculation or 0 for the first time)
 * @param buf: Data buffer that used to calculate the CRC value
 * @param len: Length of the data buffer
 * @return CRC16 value
 */
uint16_t esp_rom_crc16_le(uint16_t crc, uint8_t const *buf, uint32_t len);

/**
 * @brief CRC16 value in big endian.
 *
 * @param crc: Initial CRC value (result of last calculation or 0 for the first time)
 * @param buf: Data buffer that used to calculate the CRC value
 * @param len: Length of the data buffer
 * @return CRC16 value
 */
uint16_t esp_rom_crc16_be(uint16_t crc, uint8_t const *buf, uint32_t len);

/**
 * @brief CRC8 value in little endian.
 *
 * @param crc: Initial CRC value (result of last calculation or 0 for the first time)
 * @param buf: Data buffer that used to calculate the CRC value
 * @param len: Length of the data buffer
 * @return CRC8 value
 */
uint8_t esp_rom_crc8_le(uint8_t crc, uint8_t const *buf, uint32_t len);

/**
 * @brief CRC8 value in big endian.
 *
 * @param crc: Initial CRC value (result of last calculation or 0 for the first time)
 * @param buf: Data buffer that used to calculate the CRC value
 * @param len: Length of the data buffer
 * @return CRC8 value
 */
uint8_t esp_rom_crc8_be(uint8_t crc, uint8_t const *buf, uint32_t len);

#ifdef __cplusplus
}
#endif