FFI::Pointer#order not implemented

[chrisseaton]

Implemented in ffi/ffi@f8cfe29.

[eregon]

There doesn't seem to be any spec for this in FFI.
It would be helpful if some are added.

I guess you want to use the network endian (aka big endian), right? (ffi/ffi#813)

I wonder what's an efficient way to implement that.
Maybe a subclass of FFI::Pointer which swaps the resulting bytes (since order returns a new pointer)?

[chrisseaton]

Yes network order - specifically reading a BGV file.

I'll write specs, look at how it's implemented in MRI, and get back to you.

[eregon]

ffi/ffi@f8cfe29#diff-682df063515101c03cfa458badf35dbcR49 is how it's implemented in that commit you linked.
So checking everytime if the flag if set, and if so use some bswap function to swap the bytes.

Seems some overhead for non-swapped cases, so I think the subclass is better if compatible enough.

[chrisseaton]

Specifying upstream first in order to clarify the behaviour ffi/ffi#830.

[chrisseaton]

I'm waiting for a release of ffi to update for it.

[eregon]

I'll update to the latest FFI specs, I think we don't need a FFI release for that.

[eregon]

@chrisseaton Specs updated in b06882f, that includes the order specs.
FWIW, I noticed there is things like Long.reverseBytes() in Java which might be useful.
pack/unpack1 can also be useful to reverse, but seems much more heavy.

I'd recommend returning an instance of a FFI::Pointer subclass with reversed access, much like https://github.com/oracle/graal/blob/4bbaeaaa8d0b58134040127e416bf57419b6c09c/truffle/src/com.oracle.truffle.api/src/com/oracle/truffle/api/memory/ReversedByteArraySupport.java, so we don't slow down the common case of accessing in native order.