rust-lang / rust-lang/rust-clippy
useless op on lhs of integer division or modulo
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@Twil3akine is already working on this.
Since May 10, 2026.
A-lint
good first issue
L-correctness
L-unnecessary
T-middle
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Description
(x + n + y) % n or (x + n + y) / n can simply be replaced by (x + y) % n or (x + y) / n + 1
this isn't true for the following computations on unsigned integers:
(x + n - y) % n or (x + n - y) / n
as they might go negative due to the subtraction. For explicitly evading INT_MAX issues, this lint will cause false positives, but that could be evaded by not linting if INT_MAX is mentioned somewhere near the operation.
most likely, whenever this lint triggers, it is a bug in the equation, so the suggestion doesn't fix the underlying issue, but it will raise awareness of it.
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