From 4ca769ad091ef0018f5a20effaf4b4f428a034d7 Mon Sep 17 00:00:00 2001 From: Krishna Sai Veera Reddy Date: Fri, 29 Nov 2019 15:22:44 -0700 Subject: Optimize Ord trait implementation for bool Casting the booleans to `i8`s and converting their difference into `Ordering` generates better assembly than casting them to `u8`s and comparing them. --- src/libcore/cmp.rs | 11 ++++++++++- src/libcore/tests/cmp.rs | 8 ++++++++ 2 files changed, 18 insertions(+), 1 deletion(-) (limited to 'src/libcore') diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs index eea3dc39d34..e72b6117ba8 100644 --- a/src/libcore/cmp.rs +++ b/src/libcore/cmp.rs @@ -1006,6 +1006,7 @@ pub fn max_by_key K, K: Ord>(v1: T, v2: T, mut f: F) -> T { // Implementation of PartialEq, Eq, PartialOrd and Ord for primitive types mod impls { + use crate::hint::unreachable_unchecked; use crate::cmp::Ordering::{self, Less, Greater, Equal}; macro_rules! partial_eq_impl { @@ -1126,7 +1127,15 @@ mod impls { impl Ord for bool { #[inline] fn cmp(&self, other: &bool) -> Ordering { - (*self as u8).cmp(&(*other as u8)) + // Casting to i8's and converting the difference to an Ordering generates + // more optimal assembly. + // See for more info. + match (*self as i8) - (*other as i8) { + -1 => Less, + 0 => Equal, + 1 => Greater, + _ => unsafe { unreachable_unchecked() }, + } } } diff --git a/src/libcore/tests/cmp.rs b/src/libcore/tests/cmp.rs index 5e6778e222a..56a2f4acf6e 100644 --- a/src/libcore/tests/cmp.rs +++ b/src/libcore/tests/cmp.rs @@ -9,6 +9,14 @@ fn test_int_totalord() { assert_eq!(12.cmp(&-5), Greater); } +#[test] +fn test_bool_totalord() { + assert_eq!(true.cmp(&false), Greater); + assert_eq!(false.cmp(&true), Less); + assert_eq!(true.cmp(&true), Equal); + assert_eq!(false.cmp(&false), Equal); +} + #[test] fn test_mut_int_totalord() { assert_eq!((&mut 5).cmp(&&mut 10), Less); -- cgit 1.4.1-3-g733a5