#include <Arduino.h>

// CRC-16 Polynomial (0x8005) Parameters
#define CRC16_POLYNOMIAL 0x8005
#define CRC16_INITIAL_VALUE 0x0000

// Function to calculate CRC-16 (0x8005) for a byte array using shift left operators
uint16_t calculateCRC16(const uint8_t* data, size_t length) {
  uint16_t crc = CRC16_INITIAL_VALUE;

  for (size_t i = 0; i < length; i++) {
    crc ^= ((uint16_t)data[i] << 8); // XOR with the current byte, shifted left by 8 bits

    for (int j = 0; j < 8; j++) {
      if (crc & 0x8000) {
        crc = (crc << 1) ^ CRC16_POLYNOMIAL; // Shift left and XOR with polynomial
      } else {
        crc = (crc << 1); // Shift left
      }
    }
  }

  return crc;
}

void setup() {
  Serial.begin(9600);

  // Example data
  // uint8_t data[] = {0x01, 0x02, 0x03, 0x04, 0x05};
  uint8_t data[] = {0x01, 0x55, 0xAA, 0x30, 0x31, 0xC1, 0x31, 0x32, 0x33, 0x34, 0x04}; 
  size_t dataLength = sizeof(data);

  // Calculate CRC-16 (0x8005)
  uint16_t crc = calculateCRC16(data, dataLength);

  Serial.print("Data: ");
  for (size_t i = 0; i < dataLength; i++) {
    Serial.print(data[i], HEX);
    Serial.print(" ");
  }

  Serial.print("\nCRC-16 (0x8005) with Shift Left: 0x");
  Serial.println(crc, HEX);
}

void loop() {
  // Your code here
}