Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::integer_division_remainder_used: use of `/` has been disallowed in this context

What it meansChecks for the usage of division (/) and remainder (%) operations when performed on any integer types using the default Div and Rem trait implementations. It is in the restriction group and off by default.

What you see

warning: use of `/` has been disallowed in this context
 --> main.rs:3:14
  |
3 | let my_div = 10 / 2;
  |              ^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#integer_division_remainder_used
  = note: requested on the command line with `-W clippy::integer-division-remainder-used`

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

In cryptographic contexts, division can result in timing sidechannel vulnerabilities, and needs to be replaced with constant-time code instead (e.g. Barrett reduction).

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

let my_div = 10 / 2;

Write this instead

let my_div = 10 >> 1;

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
integer_division_remainder_used = "warn"

In code

#![warn(clippy::integer_division_remainder_used)]

One run

cargo clippy -- -W clippy::integer-division-remainder-used

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.

Restrictiongroup

allowdefault level

nofixed by cargo clippy --fix

1.79.0added in Rust

Clippy's own documentation

What it does

Checks for the usage of division (/) and remainder (%) operations when performed on any integer types using the default Div and Rem trait implementations.

Why restrict this?

In cryptographic contexts, division can result in timing sidechannel vulnerabilities, and needs to be replaced with constant-time code instead (e.g. Barrett reduction).

Example

let my_div = 10 / 2;

Use instead:

let my_div = 10 >> 1;

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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