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//! Comparison traits for `[T]`.
use crate::cmp::{self, BytewiseEq, Ordering};
use crate::intrinsics::compare_bytes;
use crate::mem;
use super::from_raw_parts;
use super::memchr;
#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> PartialEq<[B]> for [A]
where
A: PartialEq<B>,
{
fn eq(&self, other: &[B]) -> bool {
SlicePartialEq::equal(self, other)
}
fn ne(&self, other: &[B]) -> bool {
SlicePartialEq::not_equal(self, other)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Eq> Eq for [T] {}
/// Implements comparison of vectors [lexicographically](Ord#lexicographical-comparison).
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Ord> Ord for [T] {
fn cmp(&self, other: &[T]) -> Ordering {
SliceOrd::compare(self, other)
}
}
/// Implements comparison of vectors [lexicographically](Ord#lexicographical-comparison).
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: PartialOrd> PartialOrd for [T] {
fn partial_cmp(&self, other: &[T]) -> Option<Ordering> {
SlicePartialOrd::partial_compare(self, other)
}
}
#[doc(hidden)]
// intermediate trait for specialization of slice's PartialEq
trait SlicePartialEq<B> {
fn equal(&self, other: &[B]) -> bool;
fn not_equal(&self, other: &[B]) -> bool {
!self.equal(other)
}
}
// Generic slice equality
impl<A, B> SlicePartialEq<B> for [A]
where
A: PartialEq<B>,
{
default fn equal(&self, other: &[B]) -> bool {
if self.len() != other.len() {
return false;
}
// Implemented as explicit indexing rather
// than zipped iterators for performance reasons.
// See PR https://github.com/rust-lang/rust/pull/116846
for idx in 0..self.len() {
// bound checks are optimized away
if self[idx] != other[idx] {
return false;
}
}
true
}
}
// When each element can be compared byte-wise, we can compare all the bytes
// from the whole size in one call to the intrinsics.
impl<A, B> SlicePartialEq<B> for [A]
where
A: BytewiseEq<B>,
{
fn equal(&self, other: &[B]) -> bool {
if self.len() != other.len() {
return false;
}
// SAFETY: `self` and `other` are references and are thus guaranteed to be valid.
// The two slices have been checked to have the same size above.
unsafe {
let size = mem::size_of_val(self);
compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
}
}
}
#[doc(hidden)]
// intermediate trait for specialization of slice's PartialOrd
trait SlicePartialOrd: Sized {
fn partial_compare(left: &[Self], right: &[Self]) -> Option<Ordering>;
}
impl<A: PartialOrd> SlicePartialOrd for A {
default fn partial_compare(left: &[A], right: &[A]) -> Option<Ordering> {
let l = cmp::min(left.len(), right.len());
// Slice to the loop iteration range to enable bound check
// elimination in the compiler
let lhs = &left[..l];
let rhs = &right[..l];
for i in 0..l {
match lhs[i].partial_cmp(&rhs[i]) {
Some(Ordering::Equal) => (),
non_eq => return non_eq,
}
}
left.len().partial_cmp(&right.len())
}
}
// This is the impl that we would like to have. Unfortunately it's not sound.
// See `partial_ord_slice.rs`.
/*
impl<A> SlicePartialOrd for A
where
A: Ord,
{
default fn partial_compare(left: &[A], right: &[A]) -> Option<Ordering> {
Some(SliceOrd::compare(left, right))
}
}
*/
impl<A: AlwaysApplicableOrd> SlicePartialOrd for A {
fn partial_compare(left: &[A], right: &[A]) -> Option<Ordering> {
Some(SliceOrd::compare(left, right))
}
}
#[rustc_specialization_trait]
trait AlwaysApplicableOrd: SliceOrd + Ord {}
macro_rules! always_applicable_ord {
($([$($p:tt)*] $t:ty,)*) => {
$(impl<$($p)*> AlwaysApplicableOrd for $t {})*
}
}
always_applicable_ord! {
[] u8, [] u16, [] u32, [] u64, [] u128, [] usize,
[] i8, [] i16, [] i32, [] i64, [] i128, [] isize,
[] bool, [] char,
[T: ?Sized] *const T, [T: ?Sized] *mut T,
[T: AlwaysApplicableOrd] &T,
[T: AlwaysApplicableOrd] &mut T,
[T: AlwaysApplicableOrd] Option<T>,
}
#[doc(hidden)]
// intermediate trait for specialization of slice's Ord
trait SliceOrd: Sized {
fn compare(left: &[Self], right: &[Self]) -> Ordering;
}
impl<A: Ord> SliceOrd for A {
default fn compare(left: &[Self], right: &[Self]) -> Ordering {
let l = cmp::min(left.len(), right.len());
// Slice to the loop iteration range to enable bound check
// elimination in the compiler
let lhs = &left[..l];
let rhs = &right[..l];
for i in 0..l {
match lhs[i].cmp(&rhs[i]) {
Ordering::Equal => (),
non_eq => return non_eq,
}
}
left.len().cmp(&right.len())
}
}
// `compare_bytes` compares a sequence of unsigned bytes lexicographically.
// this matches the order we want for [u8], but no others (not even [i8]).
impl SliceOrd for u8 {
#[inline]
fn compare(left: &[Self], right: &[Self]) -> Ordering {
// Since the length of a slice is always less than or equal to isize::MAX, this never underflows.
let diff = left.len() as isize - right.len() as isize;
// This comparison gets optimized away (on x86_64 and ARM) because the subtraction updates flags.
let len = if left.len() < right.len() { left.len() } else { right.len() };
// SAFETY: `left` and `right` are references and are thus guaranteed to be valid.
// We use the minimum of both lengths which guarantees that both regions are
// valid for reads in that interval.
let mut order = unsafe { compare_bytes(left.as_ptr(), right.as_ptr(), len) as isize };
if order == 0 {
order = diff;
}
order.cmp(&0)
}
}
pub(super) trait SliceContains: Sized {
fn slice_contains(&self, x: &[Self]) -> bool;
}
impl<T> SliceContains for T
where
T: PartialEq,
{
default fn slice_contains(&self, x: &[Self]) -> bool {
x.iter().any(|y| *y == *self)
}
}
impl SliceContains for u8 {
#[inline]
fn slice_contains(&self, x: &[Self]) -> bool {
memchr::memchr(*self, x).is_some()
}
}
impl SliceContains for i8 {
#[inline]
fn slice_contains(&self, x: &[Self]) -> bool {
let byte = *self as u8;
// SAFETY: `i8` and `u8` have the same memory layout, thus casting `x.as_ptr()`
// as `*const u8` is safe. The `x.as_ptr()` comes from a reference and is thus guaranteed
// to be valid for reads for the length of the slice `x.len()`, which cannot be larger
// than `isize::MAX`. The returned slice is never mutated.
let bytes: &[u8] = unsafe { from_raw_parts(x.as_ptr() as *const u8, x.len()) };
memchr::memchr(byte, bytes).is_some()
}
}