Modules and Inline C

[Radyr]

I'm putting together a module that needs to calculate a check sum. I have 2 working implementations that successfully calculate the check sum.
a) a cleaned up version of the chip suppliers example c code - put in as Inline C
b) a Javascript implementation

Performance wise a) is around 8 times faster than b).

Would there be any disadvantages to having Inline c code in a module ?

[gfwilliams]

Well, the Inline C code ends up having to be run through the compiler on our server first, but I don't see that's a big problem as the App Loader is able to do that (although only for ARM-based devices, not ESP32/etc). As you have both, maybe include the JS one in a comment in the file just in case?

Just to check, Espruino does have E.CRC32 built in - does that not produce the right values for you?

[Radyr]

Thanks Gordon,

I just tried the E.CRC32 in case it was the same, unfortunately its not.

The calculation seems to take just over 1ms for the c code and around 10ms for the javascript (Although I'm not giving any guarantees that it cant be improved). So its not a huge difference either way. I do like the idea of including the alternative as a comment so that the choice can be switched over later.

[fanoush]

you may try to put "jit" in the method that does the CRC computing math, maybe that would be fast enough?
https://www.espruino.com/JIT

[Radyr]

After a bit more searching it seems that the checksum is a crc-8 check, but it appears to be a different one from the OneWire definition as I couldnt get my code to produce the same values as the examples on line.

Anyway the code is working, so I'm including the version I've written in the module for now. The "jit" suggestion has improved the JavaScript implementation from 10ms to around 4.5ms, so thanks for that.

Given that the checksum is only used on a small number of writes, I've put the javascript in place and added the C version as a comment.

[gfwilliams]

That sounds great - thanks!