esp_rom_crc32_le() function

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); CRC32 value in little endian.