Add table showing complexity of operations for Input

crates/bevy_input/src/button_input.rs

@@ -29,6 +29,35 @@ use bevy_ecs::schedule::State;
 /// * Using [`ButtonInput::clear_just_pressed`] or [`ButtonInput::clear_just_released`] instead.
 /// * Calling [`ButtonInput::clear`] or [`ButtonInput::reset`] immediately after the state change.
 ///
+/// ## Performance
+///
+/// For all operations, the following conventions are used:
+/// - **n** is the number of stored inputs.
+/// - **m** is the number of input arguments passed to the method.
+/// - **\***-suffix denotes an amortized cost.
+/// - **~**-suffix denotes an expected cost.
+///
+/// See Rust's [std::collections doc on performance](https://doc.rust-lang.org/std/collections/index.html#performance) for more details on the conventions used here.
+///
+/// | **[`ButtonInput`] operations** | **Computational complexity** |
+/// |-----------------------------------|------------------------------------|
+/// | [`ButtonInput::any_just_pressed`] | *O*(m*n) |
+/// | [`ButtonInput::any_just_released`] | *O*(m*n) |
+/// | [`ButtonInput::any_pressed`] | *O*(m*n) |
+/// | [`ButtonInput::get_just_pressed`] | *O*(n) |
+/// | [`ButtonInput::get_just_released`] | *O*(n) |
+/// | [`ButtonInput::get_pressed`] | *O*(n) |
+/// | [`ButtonInput::just_pressed`] | *O*(1)~ |
+/// | [`ButtonInput::just_released`] | *O*(1)~ |
+/// | [`ButtonInput::pressed`] | *O*(1)~ |
+/// | [`ButtonInput::press`] | *O*(1)~* |
+/// | [`ButtonInput::release`] | *O*(1)~* |
+/// | [`ButtonInput::release_all`] | *O*(n)~* |
+/// | [`ButtonInput::clear_just_pressed`] | *O*(1)~ |
+/// | [`ButtonInput::clear_just_released`] | *O*(1)~ |
+/// | [`ButtonInput::reset_all`] | *O*(n) |
+/// | [`ButtonInput::clear`] | *O*(n) |
+///
 /// ## Note
 ///
 /// When adding this resource for a new input type, you should: