Byte ordering/conversion predicates?

[dgelessus]

For signed/unsigned integer conversion, at least int → uint is easily done with bitwise operators (UInt16 is Int16 /\ 0xffff). The other direction is a bit more annoying (UInt16 >= 0x8000 -> Int16 is UInt16 - 0x10000 ; Int16 = UInt16, or all in one expression: Int16 is UInt16 \/ (\0xffff * ((UInt16 >> 15) /\ 1))). A proper library or builtins for this would be more convenient of course.

Regarding converting integers from/to packed binary data, there was some related discussion a few months ago:

How to send a string + string length on a stream?

I want to write a predicate that takes a stream and a string and writes the string length first as a 64 bit integer followed by the string as UTF8 encoded. Is this in the right direction? Also: I cannot figure out how to turn a Prolog number into bytes (i.e. turn 2 into binary 0x10). Any tips there? sendString(Stream, String) :- % make sure it is UTF8 encoded set_prolog_flag(encoding, utf8), % get a set of UTF8 codes from the string stringCodes(String, Codes), % Count and …

In that thread, @peter.ludemann also suggested the internal protobuf predicates mentioned above:

SWI-Prolog/contrib-protobufs/blob/137a9d87ccc990d29e7ae337bb4a97ad8af05982/protobufs.pl#L43-L70

FWIW, I would also be interested in having binary un-/packing operations supported in SWI, and ideally not just as undocumented internal predicates that you have to call with a module prefix I haven’t done much binary data parsing/generating with SWI yet, but it’s something I want to properly try out at some point.