crc32.ino

/*
 * ESP8266 MQTT Wifi Client to Serial Bridge with NTP
 * Author: rkubera https://github.com/rkubera/
 * License: MIT
 * 
 * Copyright (c) 2013 Christopher Baker <https://christopherbaker.net>
 * 
 * SPDX-License-Identifier:  MIT
 * 
 * https://github.com/bakercp/CRC32
*/

// Conditionally use pgm memory if it is available.

static  uint32_t _state = ~0L;

#if defined(PROGMEM)
    #define FLASH_PROGMEM PROGMEM
    #define FLASH_READ_DWORD(x) (pgm_read_dword_near(x))
#else
    #define FLASH_PROGMEM
    #define FLASH_READ_DWORD(x) (*(uint32_t*)(x))
#endif

static const uint32_t crc32_table[] FLASH_PROGMEM = {
    0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
    0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
    0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
    0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c
};

void CRC32_reset() {
     _state = ~0L;
}

void CRC32_update(const uint8_t& data) {
    // via http://forum.arduino.cc/index.php?topic=91179.0
    uint8_t tbl_idx = 0;

    tbl_idx = _state ^ (data >> (0 * 4));
    _state = FLASH_READ_DWORD(crc32_table + (tbl_idx & 0x0f)) ^ (_state >> 4);
    tbl_idx = _state ^ (data >> (1 * 4));
    _state = FLASH_READ_DWORD(crc32_table + (tbl_idx & 0x0f)) ^ (_state >> 4);
}

uint32_t CRC32_finalize() {
    return ~_state;
}