Wrong checksum calculator for NMEA1083 AIS/GPS (AIVDM / G)

[YannPara]

Hello,
I think it's may have an error in checksum computation for NMEA sentence (or I use wrong your API).

Describe the bug
When decode AIS+GPS stream with Marine-API, find >95% of "Invalid data" output (but streams is decode with error<1% on others software).

To Reproduce
Sentence sample : !AIVDM,1,1,,A,133sfv002POVWD0Je4sMA:a@00S?,0*3F
Compute CRC with Marine-api : 7A
Compute CRC with online decoder (links at bottom) & other software : 3F

Sentence sample : !AIVDM,1,1,,A,13IWB67P00wdI9pKF>atlww>2@G4,0*4F
Compute CRC with Marine-api : 0F
Compute CRC with online decoder (links at bottom) & other software : 4F

For test I use directly net.sf.marineapi.nmea.sentence.SentenceValidator "public static boolean isValid(String nmea)"

Sometime compute is good, like in this sample :
!AIVDM,1,1,,B,1CI7wSg000woG1rK3DMh0q3D00RV,0*6D

Configuration :
OS: WIN11
JDK OpenJDK 17.0.3.v202205015-1416
Marine-API version 0.11.0

Additional context
Online checkSum validator N°1
Online checkSum validator N°2
Online checkSum validator N°3

** Fast fix before API-update **
Remove all characters after * before parsing, so validator skip checksum control, but real invalid data can pass.

** Better fix before API-update **
Remove all characters after * before parsing, outside API checksum validor, if OK, pass data (with no CRC) to API.

Best regards,

[ktuukkan]

Hi @YannPara, thanks for reporting!

I added some unit tests for the samples you provided, but seems I wasn't able to reproduce the mentioned incorrect sums.

Check the commit da775b2 and corresponding build, tests and sentence validation are passing with given sentences. Please see if I misunderstood the issue?

That said, I didn't run the tests against v0.11 yet, so this might have already been fixed in the latest snapshot.

[ktuukkan]

@YannPara Checked also against v0.11 tag, but still wasn't able to reproduce the issue.