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Add Kani contracts and harnesses for NonZero (Challenge 12) #600

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Add Kani contracts and harnesses for NonZero (Challenge 12) #600

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5 changes: 4 additions & 1 deletion library/core/src/num/int_macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1736,7 +1736,10 @@ macro_rules! int_impl {
let mut base = self;
let mut acc: Self = 1;

#[safety::loop_invariant(true)]
// `self == 0` covers the primitive's own harness (e.g. `0.checked_pow(n)`, where
// `acc` can reach 0); in the NonZero call path `self` is never 0, so it is dead
// but harmless there. The right disjunct (`acc != 0 && base != 0`) is the inductive core.
#[safety::loop_invariant(self == 0 || (acc != 0 && base != 0))]
loop {
if (exp & 1) == 1 {
acc = try_opt!(acc.checked_mul(base));
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