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Add more vec![... ; n] optimizations #49496

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merged 2 commits into from
Apr 5, 2018
Merged

Add more vec![... ; n] optimizations #49496

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cc939ac
Add vec![ptr::null{,_mut}(); n] optimization, like vec![0; n]
glandium Mar 30, 2018
0df837f
Add vec!['\0'; n] optimization, like vec![0; n]
glandium Apr 2, 2018
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81 changes: 55 additions & 26 deletions src/liballoc/vec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1567,40 +1567,69 @@ impl SpecFromElem for u8 {
}
}

macro_rules! impl_spec_from_elem {
impl<T: Clone + IsZero> SpecFromElem for T {
#[inline]
fn from_elem(elem: T, n: usize) -> Vec<T> {
if elem.is_zero() {
return Vec {
buf: RawVec::with_capacity_zeroed(n),
len: n,
}
}
let mut v = Vec::with_capacity(n);
v.extend_with(n, ExtendElement(elem));
v
}
}

unsafe trait IsZero {
/// Whether this value is zero
fn is_zero(&self) -> bool;
}

macro_rules! impl_is_zero {
($t: ty, $is_zero: expr) => {
impl SpecFromElem for $t {
unsafe impl IsZero for $t {
#[inline]
fn from_elem(elem: $t, n: usize) -> Vec<$t> {
if $is_zero(elem) {
return Vec {
buf: RawVec::with_capacity_zeroed(n),
len: n,
}
}
let mut v = Vec::with_capacity(n);
v.extend_with(n, ExtendElement(elem));
v
fn is_zero(&self) -> bool {
$is_zero(*self)
}
}
};
}
}

impl_spec_from_elem!(i8, |x| x == 0);
impl_spec_from_elem!(i16, |x| x == 0);
impl_spec_from_elem!(i32, |x| x == 0);
impl_spec_from_elem!(i64, |x| x == 0);
impl_spec_from_elem!(i128, |x| x == 0);
impl_spec_from_elem!(isize, |x| x == 0);
impl_is_zero!(i8, |x| x == 0);
impl_is_zero!(i16, |x| x == 0);
impl_is_zero!(i32, |x| x == 0);
impl_is_zero!(i64, |x| x == 0);
impl_is_zero!(i128, |x| x == 0);
impl_is_zero!(isize, |x| x == 0);

impl_is_zero!(u16, |x| x == 0);
impl_is_zero!(u32, |x| x == 0);
impl_is_zero!(u64, |x| x == 0);
impl_is_zero!(u128, |x| x == 0);
impl_is_zero!(usize, |x| x == 0);

impl_is_zero!(char, |x| x == '\0');

impl_is_zero!(f32, |x: f32| x.to_bits() == 0);
impl_is_zero!(f64, |x: f64| x.to_bits() == 0);

impl_spec_from_elem!(u16, |x| x == 0);
impl_spec_from_elem!(u32, |x| x == 0);
impl_spec_from_elem!(u64, |x| x == 0);
impl_spec_from_elem!(u128, |x| x == 0);
impl_spec_from_elem!(usize, |x| x == 0);
unsafe impl<T: ?Sized> IsZero for *const T {
#[inline]
fn is_zero(&self) -> bool {
(*self).is_null()
}
}

unsafe impl<T: ?Sized> IsZero for *mut T {
#[inline]
fn is_zero(&self) -> bool {
(*self).is_null()
}
}

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
Expand Down