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d2644d9fe9
Fix implementation of `Duration::checked_div` I ran across this while running some sanity checks on `time`. Quickcheck immediately found a bug, and as I'd modified the code from `std` I knew there was a bug here as well. tl;dr this code fails ([playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1189a3efcdfc192c27d6d87815359353)) ```rust use std::time::Duration; fn main() { assert_eq!( Duration::new(1, 1).checked_div(7), Some(Duration::new(0, 142_857_143)), ); } ``` The existing code determines that 1/7 = 0 (seconds), 1/7 = 0 (nanoseconds), 1 billion / 7 = 142,857,142 (extra nanoseconds). The billion comes from multiplying the remainder of the seconds (1) by the number of nanoseconds in a second. However, **this wrongly ignores any remaining nanoseconds**. This PR takes that into consideration, adds a test, and also changes the roundabout way of calculating the remainder into directly computing it. Note: This is _not_ a rounding error. This result divides evenly. `@rustbot` label +A-time +C-bug +S-waiting-on-reviewer +T-libs