From 262be13643cf5e3ff4f4e880b2dee601d4740fd8 Mon Sep 17 00:00:00 2001 From: Mike Hommey Date: Thu, 29 Mar 2018 09:34:39 +0900 Subject: Use f{32,64}::to_bits for is_zero test in vec::SpecFromElem vec::SpecFromElem provides an optimization to use calloc to fill a Vec when the element given to fill the Vec is represented by 0. For floats, the test for that currently used is `x == 0. && x.is_sign_positive()`. When compiled in a standalone function, rustc generates the following assembly: ``` xorps xmm1, xmm1 ucomisd xmm0, xmm1 setnp al sete cl and cl, al movq rax, xmm0 test rax, rax setns al and al, cl ret ``` A simpler test telling us whether the value is represented by 0, is `x.to_bits() == 0`, which rustc compiles to: ``` movq rax, xmm0 test rax, rax sete al ret ``` Not that the test is hot in any way, but it also makes it clearer what the intent in the rust code is. --- src/liballoc/vec.rs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'src/liballoc') diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs index 953f95876be..3c2f91d08e3 100644 --- a/src/liballoc/vec.rs +++ b/src/liballoc/vec.rs @@ -1574,8 +1574,8 @@ impl_spec_from_elem!(u64, |x| x == 0); impl_spec_from_elem!(u128, |x| x == 0); impl_spec_from_elem!(usize, |x| x == 0); -impl_spec_from_elem!(f32, |x: f32| x == 0. && x.is_sign_positive()); -impl_spec_from_elem!(f64, |x: f64| x == 0. && x.is_sign_positive()); +impl_spec_from_elem!(f32, |x: f32| x.to_bits() == 0); +impl_spec_from_elem!(f64, |x: f64| x.to_bits() == 0); //////////////////////////////////////////////////////////////////////////////// // Common trait implementations for Vec -- cgit 1.4.1-3-g733a5 From 6462c0bd7f03c9f1310ea9e4d259462e753e967e Mon Sep 17 00:00:00 2001 From: Mike Hommey Date: Thu, 29 Mar 2018 11:51:52 +0900 Subject: Remove unnecessary use core::hash in liballoc/boxed.rs It' only used for hash::Hasher, but Hasher is also imported. --- src/liballoc/boxed.rs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'src/liballoc') diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs index bfd806f99e7..fdc3ef4efb8 100644 --- a/src/liballoc/boxed.rs +++ b/src/liballoc/boxed.rs @@ -62,7 +62,7 @@ use core::any::Any; use core::borrow; use core::cmp::Ordering; use core::fmt; -use core::hash::{self, Hash, Hasher}; +use core::hash::{Hash, Hasher}; use core::iter::FusedIterator; use core::marker::{self, Unpin, Unsize}; use core::mem::{self, Pin}; @@ -508,7 +508,7 @@ impl Eq for Box {} #[stable(feature = "rust1", since = "1.0.0")] impl Hash for Box { - fn hash(&self, state: &mut H) { + fn hash(&self, state: &mut H) { (**self).hash(state); } } -- cgit 1.4.1-3-g733a5