Re: [lwip-users] inet_chksum.c misbehaving with compiler optimisation?

[address@hidden]

FreeRTOS Info wrote:
> Just in case anybody is watching this thread:
>
> As unlikely as this all seems, having previously isolated one file, I
> have now isolated it to a single function: lwip_standard_chksum().
>
> I have the entire applicatino running at maximum optimisation, except
> this function, and everything is happy.
>
> Put the lowest optimisation on just this single function (which is now
> in its own file), and the network works, but with a lot of corruption on
> the wire.
Like Kieran and Stephen, I wouldn't rule out the possibility of a timing 
issue, too. Especially since checksumming was the most time consuming 
task in lwIP when I last benchmarked (aside of memcpy, but I guess you 
haven't changed the amount of optimization of memcpy in your tests as it 
often comes precompiled with the C library).

Nevertheless, to prove the function fails, why don't you run a test on 
random data comparing the results of the optimized checksum function 
with a non-optimized version? You can even let that test run for a while 
if you put the two functions into the same binary. If it's a compiler 
bug or anything in that area, this test should show it.

BTW: what do mean with 'a lot of corruption on the wire', invalid 
checksums or more errors?

Simon