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// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! A dynamically-sized view into a contiguous sequence, `[T]`.
//!
//! Slices are a view into a block of memory represented as a pointer and a
//! length.
//!
//! ```
//! // slicing a Vec
//! let vec = vec![1, 2, 3];
//! let int_slice = &vec[..];
//! // coercing an array to a slice
//! let str_slice: &[&str] = &["one", "two", "three"];
//! ```
//!
//! Slices are either mutable or shared. The shared slice type is `&[T]`,
//! while the mutable slice type is `&mut [T]`, where `T` represents the element
//! type. For example, you can mutate the block of memory that a mutable slice
//! points to:
//!
//! ```
//! let x = &mut [1, 2, 3];
//! x[1] = 7;
//! assert_eq!(x, &[1, 7, 3]);
//! ```
//!
//! Here are some of the things this module contains:
//!
//! ## Structs
//!
//! There are several structs that are useful for slices, such as [`Iter`], which
//! represents iteration over a slice.
//!
//! ## Trait Implementations
//!
//! There are several implementations of common traits for slices. Some examples
//! include:
//!
//! * [`Clone`]
//! * [`Eq`], [`Ord`] - for slices whose element type are [`Eq`] or [`Ord`].
//! * [`Hash`] - for slices whose element type is [`Hash`].
//!
//! ## Iteration
//!
//! The slices implement `IntoIterator`. The iterator yields references to the
//! slice elements.
//!
//! ```
//! let numbers = &[0, 1, 2];
//! for n in numbers {
//! println!("{} is a number!", n);
//! }
//! ```
//!
//! The mutable slice yields mutable references to the elements:
//!
//! ```
//! let mut scores = [7, 8, 9];
//! for score in &mut scores[..] {
//! *score += 1;
//! }
//! ```
//!
//! This iterator yields mutable references to the slice's elements, so while
//! the element type of the slice is `i32`, the element type of the iterator is
//! `&mut i32`.
//!
//! * [`.iter()`] and [`.iter_mut()`] are the explicit methods to return the default
//! iterators.
//! * Further methods that return iterators are [`.split()`], [`.splitn()`],
//! [`.chunks()`], [`.windows()`] and more.
//!
//! *[See also the slice primitive type](../../std/primitive.slice.html).*
//!
//! [`Clone`]: ../../std/clone/trait.Clone.html
//! [`Eq`]: ../../std/cmp/trait.Eq.html
//! [`Ord`]: ../../std/cmp/trait.Ord.html
//! [`Iter`]: struct.Iter.html
//! [`Hash`]: ../../std/hash/trait.Hash.html
//! [`.iter()`]: ../../std/primitive.slice.html#method.iter
//! [`.iter_mut()`]: ../../std/primitive.slice.html#method.iter_mut
//! [`.split()`]: ../../std/primitive.slice.html#method.split
//! [`.splitn()`]: ../../std/primitive.slice.html#method.splitn
//! [`.chunks()`]: ../../std/primitive.slice.html#method.chunks
//! [`.windows()`]: ../../std/primitive.slice.html#method.windows
#![stable(feature = "rust1", since = "1.0.0")]
// Many of the usings in this module are only used in the test configuration.
// It's cleaner to just turn off the unused_imports warning than to fix them.
#![cfg_attr(test, allow(unused_imports, dead_code))]
use alloc::boxed::Box;
use core::cmp::Ordering::{self, Greater};
use core::mem::size_of;
use core::mem;
use core::ptr;
use core::slice as core_slice;
use borrow::{Borrow, BorrowMut, ToOwned};
use vec::Vec;
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::slice::{Chunks, Windows};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::slice::{Iter, IterMut};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::slice::{SplitMut, ChunksMut, Split};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::slice::{SplitN, RSplitN, SplitNMut, RSplitNMut};
#[stable(feature = "rust1", since = "1.0.0")]
pub use core::slice::{from_raw_parts, from_raw_parts_mut};
#[unstable(feature = "slice_get_slice", issue = "35729")]
pub use core::slice::SliceIndex;
////////////////////////////////////////////////////////////////////////////////
// Basic slice extension methods
////////////////////////////////////////////////////////////////////////////////
// HACK(japaric) needed for the implementation of `vec!` macro during testing
// NB see the hack module in this file for more details
#[cfg(test)]
pub use self::hack::into_vec;
// HACK(japaric) needed for the implementation of `Vec::clone` during testing
// NB see the hack module in this file for more details
#[cfg(test)]
pub use self::hack::to_vec;
// HACK(japaric): With cfg(test) `impl [T]` is not available, these three
// functions are actually methods that are in `impl [T]` but not in
// `core::slice::SliceExt` - we need to supply these functions for the
// `test_permutations` test
mod hack {
use alloc::boxed::Box;
use core::mem;
#[cfg(test)]
use string::ToString;
use vec::Vec;
pub fn into_vec<T>(mut b: Box<[T]>) -> Vec<T> {
unsafe {
let xs = Vec::from_raw_parts(b.as_mut_ptr(), b.len(), b.len());
mem::forget(b);
xs
}
}
#[inline]
pub fn to_vec<T>(s: &[T]) -> Vec<T>
where T: Clone
{
let mut vector = Vec::with_capacity(s.len());
vector.extend_from_slice(s);
vector
}
}
#[lang = "slice"]
#[cfg(not(test))]
impl<T> [T] {
/// Returns the number of elements in the slice.
///
/// # Example
///
/// ```
/// let a = [1, 2, 3];
/// assert_eq!(a.len(), 3);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn len(&self) -> usize {
core_slice::SliceExt::len(self)
}
/// Returns `true` if the slice has a length of 0.
///
/// # Example
///
/// ```
/// let a = [1, 2, 3];
/// assert!(!a.is_empty());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn is_empty(&self) -> bool {
core_slice::SliceExt::is_empty(self)
}
/// Returns the first element of a slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert_eq!(Some(&10), v.first());
///
/// let w: &[i32] = &[];
/// assert_eq!(None, w.first());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn first(&self) -> Option<&T> {
core_slice::SliceExt::first(self)
}
/// Returns a mutable pointer to the first element of a slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(first) = x.first_mut() {
/// *first = 5;
/// }
/// assert_eq!(x, &[5, 1, 2]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn first_mut(&mut self) -> Option<&mut T> {
core_slice::SliceExt::first_mut(self)
}
/// Returns the first and all the rest of the elements of a slice.
///
/// # Examples
///
/// ```
/// let x = &[0, 1, 2];
///
/// if let Some((first, elements)) = x.split_first() {
/// assert_eq!(first, &0);
/// assert_eq!(elements, &[1, 2]);
/// }
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[inline]
pub fn split_first(&self) -> Option<(&T, &[T])> {
core_slice::SliceExt::split_first(self)
}
/// Returns the first and all the rest of the elements of a slice.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some((first, elements)) = x.split_first_mut() {
/// *first = 3;
/// elements[0] = 4;
/// elements[1] = 5;
/// }
/// assert_eq!(x, &[3, 4, 5]);
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[inline]
pub fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
core_slice::SliceExt::split_first_mut(self)
}
/// Returns the last and all the rest of the elements of a slice.
///
/// # Examples
///
/// ```
/// let x = &[0, 1, 2];
///
/// if let Some((last, elements)) = x.split_last() {
/// assert_eq!(last, &2);
/// assert_eq!(elements, &[0, 1]);
/// }
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[inline]
pub fn split_last(&self) -> Option<(&T, &[T])> {
core_slice::SliceExt::split_last(self)
}
/// Returns the last and all the rest of the elements of a slice.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some((last, elements)) = x.split_last_mut() {
/// *last = 3;
/// elements[0] = 4;
/// elements[1] = 5;
/// }
/// assert_eq!(x, &[4, 5, 3]);
/// ```
#[stable(feature = "slice_splits", since = "1.5.0")]
#[inline]
pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
core_slice::SliceExt::split_last_mut(self)
}
/// Returns the last element of a slice, or `None` if it is empty.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert_eq!(Some(&30), v.last());
///
/// let w: &[i32] = &[];
/// assert_eq!(None, w.last());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn last(&self) -> Option<&T> {
core_slice::SliceExt::last(self)
}
/// Returns a mutable pointer to the last item in the slice.
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(last) = x.last_mut() {
/// *last = 10;
/// }
/// assert_eq!(x, &[0, 1, 10]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn last_mut(&mut self) -> Option<&mut T> {
core_slice::SliceExt::last_mut(self)
}
/// Returns a reference to an element or subslice depending on the type of
/// index.
///
/// - If given a position, returns a reference to the element at that
/// position or `None` if out of bounds.
/// - If given a range, returns the subslice corresponding to that range,
/// or `None` if out of bounds.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert_eq!(Some(&40), v.get(1));
/// assert_eq!(Some(&[10, 40][..]), v.get(0..2));
/// assert_eq!(None, v.get(3));
/// assert_eq!(None, v.get(0..4));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn get<I>(&self, index: I) -> Option<&I::Output>
where I: SliceIndex<T>
{
core_slice::SliceExt::get(self, index)
}
/// Returns a mutable reference to an element or subslice depending on the
/// type of index (see [`get()`]) or `None` if the index is out of bounds.
///
/// [`get()`]: #method.get
///
/// # Examples
///
/// ```
/// let x = &mut [0, 1, 2];
///
/// if let Some(elem) = x.get_mut(1) {
/// *elem = 42;
/// }
/// assert_eq!(x, &[0, 42, 2]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn get_mut<I>(&mut self, index: I) -> Option<&mut I::Output>
where I: SliceIndex<T>
{
core_slice::SliceExt::get_mut(self, index)
}
/// Returns a reference to an element or subslice, without doing bounds
/// checking. So use it very carefully!
///
/// # Examples
///
/// ```
/// let x = &[1, 2, 4];
///
/// unsafe {
/// assert_eq!(x.get_unchecked(1), &2);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub unsafe fn get_unchecked<I>(&self, index: I) -> &I::Output
where I: SliceIndex<T>
{
core_slice::SliceExt::get_unchecked(self, index)
}
/// Returns a mutable reference to an element or subslice, without doing
/// bounds checking. So use it very carefully!
///
/// # Examples
///
/// ```
/// let x = &mut [1, 2, 4];
///
/// unsafe {
/// let elem = x.get_unchecked_mut(1);
/// *elem = 13;
/// }
/// assert_eq!(x, &[1, 13, 4]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub unsafe fn get_unchecked_mut<I>(&mut self, index: I) -> &mut I::Output
where I: SliceIndex<T>
{
core_slice::SliceExt::get_unchecked_mut(self, index)
}
/// Returns a raw pointer to the slice's buffer.
///
/// The caller must ensure that the slice outlives the pointer this
/// function returns, or else it will end up pointing to garbage.
///
/// Modifying the slice may cause its buffer to be reallocated, which
/// would also make any pointers to it invalid.
///
/// # Examples
///
/// ```
/// let x = &[1, 2, 4];
/// let x_ptr = x.as_ptr();
///
/// unsafe {
/// for i in 0..x.len() {
/// assert_eq!(x.get_unchecked(i), &*x_ptr.offset(i as isize));
/// }
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn as_ptr(&self) -> *const T {
core_slice::SliceExt::as_ptr(self)
}
/// Returns an unsafe mutable pointer to the slice's buffer.
///
/// The caller must ensure that the slice outlives the pointer this
/// function returns, or else it will end up pointing to garbage.
///
/// Modifying the slice may cause its buffer to be reallocated, which
/// would also make any pointers to it invalid.
///
/// # Examples
///
/// ```
/// let x = &mut [1, 2, 4];
/// let x_ptr = x.as_mut_ptr();
///
/// unsafe {
/// for i in 0..x.len() {
/// *x_ptr.offset(i as isize) += 2;
/// }
/// }
/// assert_eq!(x, &[3, 4, 6]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn as_mut_ptr(&mut self) -> *mut T {
core_slice::SliceExt::as_mut_ptr(self)
}
/// Swaps two elements in a slice.
///
/// # Arguments
///
/// * a - The index of the first element
/// * b - The index of the second element
///
/// # Panics
///
/// Panics if `a` or `b` are out of bounds.
///
/// # Examples
///
/// ```
/// let mut v = ["a", "b", "c", "d"];
/// v.swap(1, 3);
/// assert!(v == ["a", "d", "c", "b"]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn swap(&mut self, a: usize, b: usize) {
core_slice::SliceExt::swap(self, a, b)
}
/// Reverse the order of elements in a slice, in place.
///
/// # Example
///
/// ```
/// let mut v = [1, 2, 3];
/// v.reverse();
/// assert!(v == [3, 2, 1]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn reverse(&mut self) {
core_slice::SliceExt::reverse(self)
}
/// Returns an iterator over the slice.
///
/// # Examples
///
/// ```
/// let x = &[1, 2, 4];
/// let mut iterator = x.iter();
///
/// assert_eq!(iterator.next(), Some(&1));
/// assert_eq!(iterator.next(), Some(&2));
/// assert_eq!(iterator.next(), Some(&4));
/// assert_eq!(iterator.next(), None);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn iter(&self) -> Iter<T> {
core_slice::SliceExt::iter(self)
}
/// Returns an iterator that allows modifying each value.
///
/// # Examples
///
/// ```
/// let x = &mut [1, 2, 4];
/// for elem in x.iter_mut() {
/// *elem += 2;
/// }
/// assert_eq!(x, &[3, 4, 6]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn iter_mut(&mut self) -> IterMut<T> {
core_slice::SliceExt::iter_mut(self)
}
/// Returns an iterator over all contiguous windows of length
/// `size`. The windows overlap. If the slice is shorter than
/// `size`, the iterator returns no values.
///
/// # Panics
///
/// Panics if `size` is 0.
///
/// # Example
///
/// ```
/// let slice = ['r', 'u', 's', 't'];
/// let mut iter = slice.windows(2);
/// assert_eq!(iter.next().unwrap(), &['r', 'u']);
/// assert_eq!(iter.next().unwrap(), &['u', 's']);
/// assert_eq!(iter.next().unwrap(), &['s', 't']);
/// assert!(iter.next().is_none());
/// ```
///
/// If the slice is shorter than `size`:
///
/// ```
/// let slice = ['f', 'o', 'o'];
/// let mut iter = slice.windows(4);
/// assert!(iter.next().is_none());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn windows(&self, size: usize) -> Windows<T> {
core_slice::SliceExt::windows(self, size)
}
/// Returns an iterator over `size` elements of the slice at a
/// time. The chunks are slices and do not overlap. If `size` does
/// not divide the length of the slice, then the last chunk will
/// not have length `size`.
///
/// # Panics
///
/// Panics if `size` is 0.
///
/// # Example
///
/// ```
/// let slice = ['l', 'o', 'r', 'e', 'm'];
/// let mut iter = slice.chunks(2);
/// assert_eq!(iter.next().unwrap(), &['l', 'o']);
/// assert_eq!(iter.next().unwrap(), &['r', 'e']);
/// assert_eq!(iter.next().unwrap(), &['m']);
/// assert!(iter.next().is_none());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn chunks(&self, size: usize) -> Chunks<T> {
core_slice::SliceExt::chunks(self, size)
}
/// Returns an iterator over `chunk_size` elements of the slice at a time.
/// The chunks are mutable slices, and do not overlap. If `chunk_size` does
/// not divide the length of the slice, then the last chunk will not
/// have length `chunk_size`.
///
/// # Panics
///
/// Panics if `chunk_size` is 0.
///
/// # Examples
///
/// ```
/// let v = &mut [0, 0, 0, 0, 0];
/// let mut count = 1;
///
/// for chunk in v.chunks_mut(2) {
/// for elem in chunk.iter_mut() {
/// *elem += count;
/// }
/// count += 1;
/// }
/// assert_eq!(v, &[1, 1, 2, 2, 3]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<T> {
core_slice::SliceExt::chunks_mut(self, chunk_size)
}
/// Divides one slice into two at an index.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// # Panics
///
/// Panics if `mid > len`.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30, 20, 50];
/// let (v1, v2) = v.split_at(2);
/// assert_eq!([10, 40], v1);
/// assert_eq!([30, 20, 50], v2);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
core_slice::SliceExt::split_at(self, mid)
}
/// Divides one `&mut` into two at an index.
///
/// The first will contain all indices from `[0, mid)` (excluding
/// the index `mid` itself) and the second will contain all
/// indices from `[mid, len)` (excluding the index `len` itself).
///
/// # Panics
///
/// Panics if `mid > len`.
///
/// # Examples
///
/// ```
/// let mut v = [1, 2, 3, 4, 5, 6];
///
/// // scoped to restrict the lifetime of the borrows
/// {
/// let (left, right) = v.split_at_mut(0);
/// assert!(left == []);
/// assert!(right == [1, 2, 3, 4, 5, 6]);
/// }
///
/// {
/// let (left, right) = v.split_at_mut(2);
/// assert!(left == [1, 2]);
/// assert!(right == [3, 4, 5, 6]);
/// }
///
/// {
/// let (left, right) = v.split_at_mut(6);
/// assert!(left == [1, 2, 3, 4, 5, 6]);
/// assert!(right == []);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
core_slice::SliceExt::split_at_mut(self, mid)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`. The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let slice = [10, 40, 33, 20];
/// let mut iter = slice.split(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10, 40]);
/// assert_eq!(iter.next().unwrap(), &[20]);
/// assert!(iter.next().is_none());
/// ```
///
/// If the first element is matched, an empty slice will be the first item
/// returned by the iterator. Similarly, if the last element in the slice
/// is matched, an empty slice will be the last item returned by the
/// iterator:
///
/// ```
/// let slice = [10, 40, 33];
/// let mut iter = slice.split(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10, 40]);
/// assert_eq!(iter.next().unwrap(), &[]);
/// assert!(iter.next().is_none());
/// ```
///
/// If two matched elements are directly adjacent, an empty slice will be
/// present between them:
///
/// ```
/// let slice = [10, 6, 33, 20];
/// let mut iter = slice.split(|num| num % 3 == 0);
///
/// assert_eq!(iter.next().unwrap(), &[10]);
/// assert_eq!(iter.next().unwrap(), &[]);
/// assert_eq!(iter.next().unwrap(), &[20]);
/// assert!(iter.next().is_none());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split<F>(&self, pred: F) -> Split<T, F>
where F: FnMut(&T) -> bool
{
core_slice::SliceExt::split(self, pred)
}
/// Returns an iterator over mutable subslices separated by elements that
/// match `pred`. The matched element is not contained in the subslices.
///
/// # Examples
///
/// ```
/// let mut v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.split_mut(|num| *num % 3 == 0) {
/// group[0] = 1;
/// }
/// assert_eq!(v, [1, 40, 30, 1, 60, 1]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<T, F>
where F: FnMut(&T) -> bool
{
core_slice::SliceExt::split_mut(self, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`, limited to returning at most `n` items. The matched element is
/// not contained in the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// Print the slice split once by numbers divisible by 3 (i.e. `[10, 40]`,
/// `[20, 60, 50]`):
///
/// ```
/// let v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.splitn(2, |num| *num % 3 == 0) {
/// println!("{:?}", group);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<T, F>
where F: FnMut(&T) -> bool
{
core_slice::SliceExt::splitn(self, n, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred`, limited to returning at most `n` items. The matched element is
/// not contained in the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// ```
/// let mut v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.splitn_mut(2, |num| *num % 3 == 0) {
/// group[0] = 1;
/// }
/// assert_eq!(v, [1, 40, 30, 1, 60, 50]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<T, F>
where F: FnMut(&T) -> bool
{
core_slice::SliceExt::splitn_mut(self, n, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred` limited to returning at most `n` items. This starts at the end of
/// the slice and works backwards. The matched element is not contained in
/// the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// Print the slice split once, starting from the end, by numbers divisible
/// by 3 (i.e. `[50]`, `[10, 40, 30, 20]`):
///
/// ```
/// let v = [10, 40, 30, 20, 60, 50];
///
/// for group in v.rsplitn(2, |num| *num % 3 == 0) {
/// println!("{:?}", group);
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<T, F>
where F: FnMut(&T) -> bool
{
core_slice::SliceExt::rsplitn(self, n, pred)
}
/// Returns an iterator over subslices separated by elements that match
/// `pred` limited to returning at most `n` items. This starts at the end of
/// the slice and works backwards. The matched element is not contained in
/// the subslices.
///
/// The last element returned, if any, will contain the remainder of the
/// slice.
///
/// # Examples
///
/// ```
/// let mut s = [10, 40, 30, 20, 60, 50];
///
/// for group in s.rsplitn_mut(2, |num| *num % 3 == 0) {
/// group[0] = 1;
/// }
/// assert_eq!(s, [1, 40, 30, 20, 60, 1]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<T, F>
where F: FnMut(&T) -> bool
{
core_slice::SliceExt::rsplitn_mut(self, n, pred)
}
/// Returns `true` if the slice contains an element with the given value.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.contains(&30));
/// assert!(!v.contains(&50));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn contains(&self, x: &T) -> bool
where T: PartialEq
{
core_slice::SliceExt::contains(self, x)
}
/// Returns `true` if `needle` is a prefix of the slice.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.starts_with(&[10]));
/// assert!(v.starts_with(&[10, 40]));
/// assert!(!v.starts_with(&[50]));
/// assert!(!v.starts_with(&[10, 50]));
/// ```
///
/// Always returns `true` if `needle` is an empty slice:
///
/// ```
/// let v = &[10, 40, 30];
/// assert!(v.starts_with(&[]));
/// let v: &[u8] = &[];
/// assert!(v.starts_with(&[]));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn starts_with(&self, needle: &[T]) -> bool
where T: PartialEq
{
core_slice::SliceExt::starts_with(self, needle)
}
/// Returns `true` if `needle` is a suffix of the slice.
///
/// # Examples
///
/// ```
/// let v = [10, 40, 30];
/// assert!(v.ends_with(&[30]));
/// assert!(v.ends_with(&[40, 30]));
/// assert!(!v.ends_with(&[50]));
/// assert!(!v.ends_with(&[50, 30]));
/// ```
///
/// Always returns `true` if `needle` is an empty slice:
///
/// ```
/// let v = &[10, 40, 30];
/// assert!(v.ends_with(&[]));
/// let v: &[u8] = &[];
/// assert!(v.ends_with(&[]));
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn ends_with(&self, needle: &[T]) -> bool
where T: PartialEq
{
core_slice::SliceExt::ends_with(self, needle)
}
/// Binary search a sorted slice for a given element.
///
/// If the value is found then `Ok` is returned, containing the
/// index of the matching element; if the value is not found then
/// `Err` is returned, containing the index where a matching
/// element could be inserted while maintaining sorted order.
///
/// # Example
///
/// Looks up a series of four elements. The first is found, with a
/// uniquely determined position; the second and third are not
/// found; the fourth could match any position in `[1, 4]`.
///
/// ```
/// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
///
/// assert_eq!(s.binary_search(&13), Ok(9));
/// assert_eq!(s.binary_search(&4), Err(7));
/// assert_eq!(s.binary_search(&100), Err(13));
/// let r = s.binary_search(&1);
/// assert!(match r { Ok(1...4) => true, _ => false, });
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn binary_search(&self, x: &T) -> Result<usize, usize>
where T: Ord
{
core_slice::SliceExt::binary_search(self, x)
}
/// Binary search a sorted slice with a comparator function.
///
/// The comparator function should implement an order consistent
/// with the sort order of the underlying slice, returning an
/// order code that indicates whether its argument is `Less`,
/// `Equal` or `Greater` the desired target.
///
/// If a matching value is found then returns `Ok`, containing
/// the index for the matched element; if no match is found then
/// `Err` is returned, containing the index where a matching
/// element could be inserted while maintaining sorted order.
///
/// # Example
///
/// Looks up a series of four elements. The first is found, with a
/// uniquely determined position; the second and third are not
/// found; the fourth could match any position in `[1, 4]`.
///
/// ```
/// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
///
/// let seek = 13;
/// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
/// let seek = 4;
/// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
/// let seek = 100;
/// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
/// let seek = 1;
/// let r = s.binary_search_by(|probe| probe.cmp(&seek));
/// assert!(match r { Ok(1...4) => true, _ => false, });
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn binary_search_by<'a, F>(&'a self, f: F) -> Result<usize, usize>
where F: FnMut(&'a T) -> Ordering
{
core_slice::SliceExt::binary_search_by(self, f)
}
/// Binary search a sorted slice with a key extraction function.
///
/// Assumes that the slice is sorted by the key, for instance with
/// [`sort_by_key`] using the same key extraction function.
///
/// If a matching value is found then returns `Ok`, containing the
/// index for the matched element; if no match is found then `Err`
/// is returned, containing the index where a matching element could
/// be inserted while maintaining sorted order.
///
/// [`sort_by_key`]: #method.sort_by_key
///
/// # Examples
///
/// Looks up a series of four elements in a slice of pairs sorted by
/// their second elements. The first is found, with a uniquely
/// determined position; the second and third are not found; the
/// fourth could match any position in `[1, 4]`.
///
/// ```
/// let s = [(0, 0), (2, 1), (4, 1), (5, 1), (3, 1),
/// (1, 2), (2, 3), (4, 5), (5, 8), (3, 13),
/// (1, 21), (2, 34), (4, 55)];
///
/// assert_eq!(s.binary_search_by_key(&13, |&(a,b)| b), Ok(9));
/// assert_eq!(s.binary_search_by_key(&4, |&(a,b)| b), Err(7));
/// assert_eq!(s.binary_search_by_key(&100, |&(a,b)| b), Err(13));
/// let r = s.binary_search_by_key(&1, |&(a,b)| b);
/// assert!(match r { Ok(1...4) => true, _ => false, });
/// ```
#[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
#[inline]
pub fn binary_search_by_key<'a, B, F>(&'a self, b: &B, f: F) -> Result<usize, usize>
where F: FnMut(&'a T) -> B,
B: Ord
{
core_slice::SliceExt::binary_search_by_key(self, b, f)
}
/// This is equivalent to `self.sort_by(|a, b| a.cmp(b))`.
///
/// This sort is stable (i.e. does not reorder equal elements) and `O(n log n)` worst-case.
///
/// # Current implementation
///
/// The current algorithm is an adaptive, iterative merge sort inspired by
/// [timsort](https://en.wikipedia.org/wiki/Timsort).
/// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
/// two or more sorted sequences concatenated one after another.
///
/// Also, it allocates temporary storage half the size of `self`, but for short slices a
/// non-allocating insertion sort is used instead.
///
/// # Examples
///
/// ```
/// let mut v = [-5, 4, 1, -3, 2];
///
/// v.sort();
/// assert!(v == [-5, -3, 1, 2, 4]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn sort(&mut self)
where T: Ord
{
self.sort_by(|a, b| a.cmp(b))
}
/// Sorts the slice using `f` to extract a key to compare elements by.
///
/// This sort is stable (i.e. does not reorder equal elements) and `O(n log n)` worst-case.
///
/// # Current implementation
///
/// The current algorithm is an adaptive, iterative merge sort inspired by
/// [timsort](https://en.wikipedia.org/wiki/Timsort).
/// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
/// two or more sorted sequences concatenated one after another.
///
/// Also, it allocates temporary storage half the size of `self`, but for short slices a
/// non-allocating insertion sort is used instead.
///
/// # Examples
///
/// ```
/// let mut v = [-5i32, 4, 1, -3, 2];
///
/// v.sort_by_key(|k| k.abs());
/// assert!(v == [1, 2, -3, 4, -5]);
/// ```
#[stable(feature = "slice_sort_by_key", since = "1.7.0")]
#[inline]
pub fn sort_by_key<B, F>(&mut self, mut f: F)
where F: FnMut(&T) -> B, B: Ord
{
self.sort_by(|a, b| f(a).cmp(&f(b)))
}
/// Sorts the slice using `compare` to compare elements.
///
/// This sort is stable (i.e. does not reorder equal elements) and `O(n log n)` worst-case.
///
/// # Current implementation
///
/// The current algorithm is an adaptive, iterative merge sort inspired by
/// [timsort](https://en.wikipedia.org/wiki/Timsort).
/// It is designed to be very fast in cases where the slice is nearly sorted, or consists of
/// two or more sorted sequences concatenated one after another.
///
/// Also, it allocates temporary storage half the size of `self`, but for short slices a
/// non-allocating insertion sort is used instead.
///
/// # Examples
///
/// ```
/// let mut v = [5, 4, 1, 3, 2];
/// v.sort_by(|a, b| a.cmp(b));
/// assert!(v == [1, 2, 3, 4, 5]);
///
/// // reverse sorting
/// v.sort_by(|a, b| b.cmp(a));
/// assert!(v == [5, 4, 3, 2, 1]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn sort_by<F>(&mut self, compare: F)
where F: FnMut(&T, &T) -> Ordering
{
merge_sort(self, compare)
}
/// Copies the elements from `src` into `self`.
///
/// The length of `src` must be the same as `self`.
///
/// # Panics
///
/// This function will panic if the two slices have different lengths.
///
/// # Example
///
/// ```
/// let mut dst = [0, 0, 0];
/// let src = [1, 2, 3];
///
/// dst.clone_from_slice(&src);
/// assert!(dst == [1, 2, 3]);
/// ```
#[stable(feature = "clone_from_slice", since = "1.7.0")]
pub fn clone_from_slice(&mut self, src: &[T]) where T: Clone {
core_slice::SliceExt::clone_from_slice(self, src)
}
/// Copies all elements from `src` into `self`, using a memcpy.
///
/// The length of `src` must be the same as `self`.
///
/// # Panics
///
/// This function will panic if the two slices have different lengths.
///
/// # Example
///
/// ```
/// let mut dst = [0, 0, 0];
/// let src = [1, 2, 3];
///
/// dst.copy_from_slice(&src);
/// assert_eq!(src, dst);
/// ```
#[stable(feature = "copy_from_slice", since = "1.9.0")]
pub fn copy_from_slice(&mut self, src: &[T]) where T: Copy {
core_slice::SliceExt::copy_from_slice(self, src)
}
/// Copies `self` into a new `Vec`.
///
/// # Examples
///
/// ```
/// let s = [10, 40, 30];
/// let x = s.to_vec();
/// // Here, `s` and `x` can be modified independently.
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn to_vec(&self) -> Vec<T>
where T: Clone
{
// NB see hack module in this file
hack::to_vec(self)
}
/// Converts `self` into a vector without clones or allocation.
///
/// # Examples
///
/// ```
/// let s: Box<[i32]> = Box::new([10, 40, 30]);
/// let x = s.into_vec();
/// // `s` cannot be used anymore because it has been converted into `x`.
///
/// assert_eq!(x, vec![10, 40, 30]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn into_vec(self: Box<Self>) -> Vec<T> {
// NB see hack module in this file
hack::into_vec(self)
}
}
////////////////////////////////////////////////////////////////////////////////
// Extension traits for slices over specific kinds of data
////////////////////////////////////////////////////////////////////////////////
#[unstable(feature = "slice_concat_ext",
reason = "trait should not have to exist",
issue = "27747")]
/// An extension trait for concatenating slices
pub trait SliceConcatExt<T: ?Sized> {
#[unstable(feature = "slice_concat_ext",
reason = "trait should not have to exist",
issue = "27747")]
/// The resulting type after concatenation
type Output;
/// Flattens a slice of `T` into a single value `Self::Output`.
///
/// # Examples
///
/// ```
/// assert_eq!(["hello", "world"].concat(), "helloworld");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn concat(&self) -> Self::Output;
/// Flattens a slice of `T` into a single value `Self::Output`, placing a
/// given separator between each.
///
/// # Examples
///
/// ```
/// assert_eq!(["hello", "world"].join(" "), "hello world");
/// ```
#[stable(feature = "rename_connect_to_join", since = "1.3.0")]
fn join(&self, sep: &T) -> Self::Output;
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_deprecated(since = "1.3.0", reason = "renamed to join")]
fn connect(&self, sep: &T) -> Self::Output;
}
#[unstable(feature = "slice_concat_ext",
reason = "trait should not have to exist",
issue = "27747")]
impl<T: Clone, V: Borrow<[T]>> SliceConcatExt<T> for [V] {
type Output = Vec<T>;
fn concat(&self) -> Vec<T> {
let size = self.iter().fold(0, |acc, v| acc + v.borrow().len());
let mut result = Vec::with_capacity(size);
for v in self {
result.extend_from_slice(v.borrow())
}
result
}
fn join(&self, sep: &T) -> Vec<T> {
let size = self.iter().fold(0, |acc, v| acc + v.borrow().len());
let mut result = Vec::with_capacity(size + self.len());
let mut first = true;
for v in self {
if first {
first = false
} else {
result.push(sep.clone())
}
result.extend_from_slice(v.borrow())
}
result
}
fn connect(&self, sep: &T) -> Vec<T> {
self.join(sep)
}
}
////////////////////////////////////////////////////////////////////////////////
// Standard trait implementations for slices
////////////////////////////////////////////////////////////////////////////////
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Borrow<[T]> for Vec<T> {
fn borrow(&self) -> &[T] {
&self[..]
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> BorrowMut<[T]> for Vec<T> {
fn borrow_mut(&mut self) -> &mut [T] {
&mut self[..]
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Clone> ToOwned for [T] {
type Owned = Vec<T>;
#[cfg(not(test))]
fn to_owned(&self) -> Vec<T> {
self.to_vec()
}
// HACK(japaric): with cfg(test) the inherent `[T]::to_vec`, which is required for this method
// definition, is not available. Since we don't require this method for testing purposes, I'll
// just stub it
// NB see the slice::hack module in slice.rs for more information
#[cfg(test)]
fn to_owned(&self) -> Vec<T> {
panic!("not available with cfg(test)")
}
}
////////////////////////////////////////////////////////////////////////////////
// Sorting
////////////////////////////////////////////////////////////////////////////////
/// Inserts `v[0]` into pre-sorted sequence `v[1..]` so that whole `v[..]` becomes sorted.
///
/// This is the integral subroutine of insertion sort.
fn insert_head<T, F>(v: &mut [T], compare: &mut F)
where F: FnMut(&T, &T) -> Ordering
{
if v.len() >= 2 && compare(&v[0], &v[1]) == Greater {
unsafe {
// There are three ways to implement insertion here:
//
// 1. Swap adjacent elements until the first one gets to its final destination.
// However, this way we copy data around more than is necessary. If elements are big
// structures (costly to copy), this method will be slow.
//
// 2. Iterate until the right place for the first element is found. Then shift the
// elements succeeding it to make room for it and finally place it into the
// remaining hole. This is a good method.
//
// 3. Copy the first element into a temporary variable. Iterate until the right place
// for it is found. As we go along, copy every traversed element into the slot
// preceding it. Finally, copy data from the temporary variable into the remaining
// hole. This method is very good. Benchmarks demonstrated slightly better
// performance than with the 2nd method.
//
// All methods were benchmarked, and the 3rd showed best results. So we chose that one.
let mut tmp = NoDrop { value: ptr::read(&v[0]) };
// Intermediate state of the insertion process is always tracked by `hole`, which
// serves two purposes:
// 1. Protects integrity of `v` from panics in `compare`.
// 2. Fills the remaining hole in `v` in the end.
//
// Panic safety:
//
// If `compare` panics at any point during the process, `hole` will get dropped and
// fill the hole in `v` with `tmp`, thus ensuring that `v` still holds every object it
// initially held exactly once.
let mut hole = InsertionHole {
src: &mut tmp.value,
dest: &mut v[1],
};
ptr::copy_nonoverlapping(&v[1], &mut v[0], 1);
for i in 2..v.len() {
if compare(&tmp.value, &v[i]) != Greater {
break;
}
ptr::copy_nonoverlapping(&v[i], &mut v[i - 1], 1);
hole.dest = &mut v[i];
}
// `hole` gets dropped and thus copies `tmp` into the remaining hole in `v`.
}
}
// Holds a value, but never drops it.
#[allow(unions_with_drop_fields)]
union NoDrop<T> {
value: T
}
// When dropped, copies from `src` into `dest`.
struct InsertionHole<T> {
src: *mut T,
dest: *mut T,
}
impl<T> Drop for InsertionHole<T> {
fn drop(&mut self) {
unsafe { ptr::copy_nonoverlapping(self.src, self.dest, 1); }
}
}
}
/// Merges non-decreasing runs `v[..mid]` and `v[mid..]` using `buf` as temporary storage, and
/// stores the result into `v[..]`.
///
/// # Safety
///
/// The two slices must be non-empty and `mid` must be in bounds. Buffer `buf` must be long enough
/// to hold a copy of the shorter slice. Also, `T` must not be a zero-sized type.
unsafe fn merge<T, F>(v: &mut [T], mid: usize, buf: *mut T, compare: &mut F)
where F: FnMut(&T, &T) -> Ordering
{
let len = v.len();
let v = v.as_mut_ptr();
let v_mid = v.offset(mid as isize);
let v_end = v.offset(len as isize);
// The merge process first copies the shorter run into `buf`. Then it traces the newly copied
// run and the longer run forwards (or backwards), comparing their next unconsumed elements and
// copying the lesser (or greater) one into `v`.
//
// As soon as the shorter run is fully consumed, the process is done. If the longer run gets
// consumed first, then we must copy whatever is left of the shorter run into the remaining
// hole in `v`.
//
// Intermediate state of the process is always tracked by `hole`, which serves two purposes:
// 1. Protects integrity of `v` from panics in `compare`.
// 2. Fills the remaining hole in `v` if the longer run gets consumed first.
//
// Panic safety:
//
// If `compare` panics at any point during the process, `hole` will get dropped and fill the
// hole in `v` with the unconsumed range in `buf`, thus ensuring that `v` still holds every
// object it initially held exactly once.
let mut hole;
if mid <= len - mid {
// The left run is shorter.
ptr::copy_nonoverlapping(v, buf, mid);
hole = MergeHole {
start: buf,
end: buf.offset(mid as isize),
dest: v,
};
// Initially, these pointers point to the beginnings of their arrays.
let left = &mut hole.start;
let mut right = v_mid;
let out = &mut hole.dest;
while *left < hole.end && right < v_end {
// Consume the lesser side.
// If equal, prefer the left run to maintain stability.
let to_copy = if compare(&**left, &*right) == Greater {
get_and_increment(&mut right)
} else {
get_and_increment(left)
};
ptr::copy_nonoverlapping(to_copy, get_and_increment(out), 1);
}
} else {
// The right run is shorter.
ptr::copy_nonoverlapping(v_mid, buf, len - mid);
hole = MergeHole {
start: buf,
end: buf.offset((len - mid) as isize),
dest: v_mid,
};
// Initially, these pointers point past the ends of their arrays.
let left = &mut hole.dest;
let right = &mut hole.end;
let mut out = v_end;
while v < *left && buf < *right {
// Consume the greater side.
// If equal, prefer the right run to maintain stability.
let to_copy = if compare(&*left.offset(-1), &*right.offset(-1)) == Greater {
decrement_and_get(left)
} else {
decrement_and_get(right)
};
ptr::copy_nonoverlapping(to_copy, decrement_and_get(&mut out), 1);
}
}
// Finally, `hole` gets dropped. If the shorter run was not fully consumed, whatever remains of
// it will now be copied into the hole in `v`.
unsafe fn get_and_increment<T>(ptr: &mut *mut T) -> *mut T {
let old = *ptr;
*ptr = ptr.offset(1);
old
}
unsafe fn decrement_and_get<T>(ptr: &mut *mut T) -> *mut T {
*ptr = ptr.offset(-1);
*ptr
}
// When dropped, copies the range `start..end` into `dest..`.
struct MergeHole<T> {
start: *mut T,
end: *mut T,
dest: *mut T,
}
impl<T> Drop for MergeHole<T> {
fn drop(&mut self) {
// `T` is not a zero-sized type, so it's okay to divide by it's size.
let len = (self.end as usize - self.start as usize) / mem::size_of::<T>();
unsafe { ptr::copy_nonoverlapping(self.start, self.dest, len); }
}
}
}
/// This merge sort borrows some (but not all) ideas from TimSort, which is described in detail
/// [here](http://svn.python.org/projects/python/trunk/Objects/listsort.txt).
///
/// The algorithm identifies strictly descending and non-descending subsequences, which are called
/// natural runs. There is a stack of pending runs yet to be merged. Each newly found run is pushed
/// onto the stack, and then some pairs of adjacent runs are merged until these two invariants are
/// satisfied:
///
/// 1. for every `i` in `1..runs.len()`: `runs[i - 1].len > runs[i].len`
/// 2. for every `i` in `2..runs.len()`: `runs[i - 2].len > runs[i - 1].len + runs[i].len`
///
/// The invariants ensure that the total running time is `O(n log n)` worst-case.
fn merge_sort<T, F>(v: &mut [T], mut compare: F)
where F: FnMut(&T, &T) -> Ordering
{
// Sorting has no meaningful behavior on zero-sized types.
if size_of::<T>() == 0 {
return;
}
// FIXME #12092: These numbers are platform-specific and need more extensive testing/tuning.
//
// If `v` has length up to `max_insertion`, simply switch to insertion sort because it is going
// to perform better than merge sort. For bigger types `T`, the threshold is smaller.
//
// Short runs are extended using insertion sort to span at least `min_run` elements, in order
// to improve performance.
let (max_insertion, min_run) = if size_of::<T>() <= 16 {
(64, 32)
} else {
(32, 16)
};
let len = v.len();
// Short arrays get sorted in-place via insertion sort to avoid allocations.
if len <= max_insertion {
if len >= 2 {
for i in (0..len-1).rev() {
insert_head(&mut v[i..], &mut compare);
}
}
return;
}
// Allocate a buffer to use as scratch memory. We keep the length 0 so we can keep in it
// shallow copies of the contents of `v` without risking the dtors running on copies if
// `compare` panics. When merging two sorted runs, this buffer holds a copy of the shorter run,
// which will always have length at most `len / 2`.
let mut buf = Vec::with_capacity(len / 2);
// In order to identify natural runs in `v`, we traverse it backwards. That might seem like a
// strange decision, but consider the fact that merges more often go in the opposite direction
// (forwards). According to benchmarks, merging forwards is slightly faster than merging
// backwards. To conclude, identifying runs by traversing backwards improves performance.
let mut runs = vec![];
let mut end = len;
while end > 0 {
// Find the next natural run, and reverse it if it's strictly descending.
let mut start = end - 1;
if start > 0 {
start -= 1;
if compare(&v[start], &v[start + 1]) == Greater {
while start > 0 && compare(&v[start - 1], &v[start]) == Greater {
start -= 1;
}
v[start..end].reverse();
} else {
while start > 0 && compare(&v[start - 1], &v[start]) != Greater {
start -= 1;
}
}
}
// Insert some more elements into the run if it's too short. Insertion sort is faster than
// merge sort on short sequences, so this significantly improves performance.
while start > 0 && end - start < min_run {
start -= 1;
insert_head(&mut v[start..end], &mut compare);
}
// Push this run onto the stack.
runs.push(Run {
start: start,
len: end - start,
});
end = start;
// Merge some pairs of adjacent runs to satisfy the invariants.
while let Some(r) = collapse(&runs) {
let left = runs[r + 1];
let right = runs[r];
unsafe {
merge(&mut v[left.start .. right.start + right.len], left.len, buf.as_mut_ptr(),
&mut compare);
}
runs[r] = Run {
start: left.start,
len: left.len + right.len,
};
runs.remove(r + 1);
}
}
// Finally, exactly one run must remain in the stack.
debug_assert!(runs.len() == 1 && runs[0].start == 0 && runs[0].len == len);
// Examines the stack of runs and identifies the next pair of runs to merge. More specifically,
// if `Some(r)` is returned, that means `runs[r]` and `runs[r + 1]` must be merged next. If the
// algorithm should continue building a new run instead, `None` is returned.
//
// TimSort is infamous for it's buggy implementations, as described here:
// http://envisage-project.eu/timsort-specification-and-verification/
//
// The gist of the story is: we must enforce the invariants on the top four runs on the stack.
// Enforcing them on just top three is not sufficient to ensure that the invariants will still
// hold for *all* runs in the stack.
//
// This function correctly checks invariants for the top four runs. Additionally, if the top
// run starts at index 0, it will always demand a merge operation until the stack is fully
// collapsed, in order to complete the sort.
#[inline]
fn collapse(runs: &[Run]) -> Option<usize> {
let n = runs.len();
if n >= 2 && (runs[n - 1].start == 0 ||
runs[n - 2].len <= runs[n - 1].len ||
(n >= 3 && runs[n - 3].len <= runs[n - 2].len + runs[n - 1].len) ||
(n >= 4 && runs[n - 4].len <= runs[n - 3].len + runs[n - 2].len)) {
if n >= 3 && runs[n - 3].len < runs[n - 1].len {
Some(n - 3)
} else {
Some(n - 2)
}
} else {
None
}
}
#[derive(Clone, Copy)]
struct Run {
start: usize,
len: usize,
}
}
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