In the standard there's things like "exactly N operations", but not seeing stuff for `istream`. There's like... an explanation of how things should work and I imagine you can derive complexity from it, but I think `istream` is a bit special since you're talking about this wrapper for (potentially) an arbitrary input source.

[0]: https://eel.is/c++draft/alg.move#15

[1]: https://eel.is/c++draft/input.streams#istream.extractors-7