Build error with qemu_x86_64

[jukkar]

Describe the bug
The compilation of websocket sample application in #19025 gives this build error:

In file included from .../zephyr/subsys/net/l2/ethernet/ethernet.c:16:
.../zephyr/include/net/gptp.h: In function 'gptp_pow2':
.../zephyr/include/net/gptp.h:72:1: error: SSE register return with SSE disabled
 {
 ^
make[3]: *** [zephyr/subsys/net/l2/ethernet/CMakeFiles/subsys__net__l2__ethernet.dir/build.make:63: zephyr/subsys/net/l2/ethernet/CMak

To Reproduce

1. Fetch Simple Websocket & HTTP client API support #19025
2. Remove blacklisting of qemu_x86_64 from samples/net/sockets/websocket_client/sample.yaml
3. sanitycheck -t websocket -p qemu_x86_64

Expected behavior
No error

Impact
Test fails. I will blacklist this board temporarily in order to proceed.

GCC chokes on this because x86_64 lacks support for SSE and GCC doesn't know how to pass floating-point arguments (or return floating-point values) absent SSE registers. We should probably leave the test blacklisted and close this bug.

[jukkar]

Ok, I am fine with that.

On a side, note, looking at the function:

{
        double res;

        if (exp >= 0) {
                res = 1 << exp;
        } else {
                res = 1.0;

                while (exp++) {
                        res /= 2;
                }
        }

        return res;
}

Why not avoid the iteration for negative exponents, and use 1.0 / (1 << -exp) ?

[jukkar]

Why not avoid the iteration for negative exponents, and use 1.0 / (1 << -exp) ?

If the exponent is very small, then we could get wrong result.

orig: 2^-48 = 3.55271367880050092936e-15
  v2: 2^-48 = 1.52587890625000000000e-05
orig: 2^-96 = 1.26217744835361888866e-29
  v2: 2^-96 = 1.00000000000000000000e+00

Understood. I guess you do not expect the exponent to get very large, though. So the domain isn't symmetric about 0. Makes enough sense given the context.

[jukkar]

I guess you do not expect the exponent to get very large, though. So the domain isn't symmetric about 0

Correct, the numbers related to gPTP are typically very small.

Lets close this then and I will leave the board blacklisted in this sample.