Skip to content

Challenge 12: safety and correctness of NonZero #637

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
stefanzetzsche wants to merge 1 commit into
base: main
Choose a base branch
from
+1,890 −112
Open

Challenge 12: safety and correctness of NonZero #637

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 5 additions & 1 deletion library/core/src/num/int_macros.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1755,7 +1755,11 @@ macro_rules! int_impl {
let mut base = self;
let mut acc: Self = 1;

#[safety::loop_invariant(true)]
// Inductive (`acc` starts at 1; `try_opt!` bails on overflow, so
// nonzero × nonzero stays nonzero); discharges the nonzero
// obligation in `NonZero::checked_pow`, which a `true` invariant
// cannot (loop abstraction havocs `acc`).
#[safety::loop_invariant(self == 0 || (acc != 0 && base != 0))]
loop {
if (exp & 1) == 1 {
acc = try_opt!(acc.checked_mul(base));
Expand Down
Loading
Loading