Calculate the number of bits necessary to represent the enum variant
using the next_power_of_two() and trailing_zeros() functions from the
primitive usize type.
Also add a test to ensure that the returned value is correct when there
is only one variant in the enum.
BUG=none
TEST=unit tests
Change-Id: Ibd15efd4f06e17a74489fee04ff19aca0dde68b2
Signed-off-by: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/959624
Reviewed-by: Zach Reizner <zachr@chromium.org>
Using an enum implementing PollToken is the recommended way to use
PollContext, but writing the trait impls for each enum is mechanical yet
error prone. This is a perfect candidate for a custom derive, which
automates away the process using a simple derive attribute on an enum.
BUG=chromium:816692
TEST=cargo test -p sys_util
Change-Id: If21d0f94f9af4b4f6cef1f24c78fc36b50471053
Reviewed-on: https://chromium-review.googlesource.com/940865
Commit-Ready: Zach Reizner <zachr@chromium.org>
Tested-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
