crc16_reflect() showing unexpected results

[tomschmitz98]

Hello, I am migrating a project to Zephyr and I noticed there was a CRC module in Zephyr. Since CRC16 is being used in the project that I am working on, I decided to test the module and found that crc16_reflect() was not outputting the expected value. I was wondering if I am misusing the library or if this was a genuine bug that I discovered.

example code:

#define POLYNOMIAL 0xD175

uint8_t src[] = "Hello, World.";
size_t len = sizeof(src) - 1;

uint16_t crc = crc16_reflect(POLYNOMIAL, 0, src, len);

// Expected value of crc: 0xF97E
// Received value of crc: 0x5F50

I checked the result with several web CRC calculators such as sunshine's CRC calculator

Parameters:

• Input and output reflect
• Polynomial: 0xD175
• Initial value: 0
• Final XOR value: 0

[kartben]

As per the documentation of the function, the polynomial should be reflected.

The polynomial to use omitting the leading x^16 coefficient. Important: please reflect the poly.

Using 0xae8b (0xd175 reflected) in the web calculator matches the output you're seeing :)

[tomschmitz98]

Thanks you, that works! I missed that in the docs :/