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diff --git a/rust/alloc/slice.rs b/rust/alloc/slice.rs new file mode 100644 index 000000000000..e444e97fa145 --- /dev/null +++ b/rust/alloc/slice.rs @@ -0,0 +1,1204 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +//! A dynamically-sized view into a contiguous sequence, `[T]`. +//! +//! *[See also the slice primitive type](slice).* +//! +//! 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!("{n} is a number!"); +//! } +//! ``` +//! +//! 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. +//! +//! [`Hash`]: core::hash::Hash +//! [`.iter`]: slice::iter +//! [`.iter_mut`]: slice::iter_mut +//! [`.split`]: slice::split +//! [`.splitn`]: slice::splitn +//! [`.chunks`]: slice::chunks +//! [`.windows`]: slice::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 core::borrow::{Borrow, BorrowMut}; +#[cfg(not(no_global_oom_handling))] +use core::cmp::Ordering::{self, Less}; +#[cfg(not(no_global_oom_handling))] +use core::mem; +#[cfg(not(no_global_oom_handling))] +use core::mem::size_of; +#[cfg(not(no_global_oom_handling))] +use core::ptr; + +use crate::alloc::Allocator; +#[cfg(not(no_global_oom_handling))] +use crate::alloc::Global; +#[cfg(not(no_global_oom_handling))] +use crate::borrow::ToOwned; +use crate::boxed::Box; +use crate::vec::Vec; + +#[unstable(feature = "slice_range", issue = "76393")] +pub use core::slice::range; +#[unstable(feature = "array_chunks", issue = "74985")] +pub use core::slice::ArrayChunks; +#[unstable(feature = "array_chunks", issue = "74985")] +pub use core::slice::ArrayChunksMut; +#[unstable(feature = "array_windows", issue = "75027")] +pub use core::slice::ArrayWindows; +#[stable(feature = "inherent_ascii_escape", since = "1.60.0")] +pub use core::slice::EscapeAscii; +#[stable(feature = "slice_get_slice", since = "1.28.0")] +pub use core::slice::SliceIndex; +#[stable(feature = "from_ref", since = "1.28.0")] +pub use core::slice::{from_mut, from_ref}; +#[stable(feature = "rust1", since = "1.0.0")] +pub use core::slice::{from_raw_parts, from_raw_parts_mut}; +#[stable(feature = "rust1", since = "1.0.0")] +pub use core::slice::{Chunks, Windows}; +#[stable(feature = "chunks_exact", since = "1.31.0")] +pub use core::slice::{ChunksExact, ChunksExactMut}; +#[stable(feature = "rust1", since = "1.0.0")] +pub use core::slice::{ChunksMut, Split, SplitMut}; +#[unstable(feature = "slice_group_by", issue = "80552")] +pub use core::slice::{GroupBy, GroupByMut}; +#[stable(feature = "rust1", since = "1.0.0")] +pub use core::slice::{Iter, IterMut}; +#[stable(feature = "rchunks", since = "1.31.0")] +pub use core::slice::{RChunks, RChunksExact, RChunksExactMut, RChunksMut}; +#[stable(feature = "slice_rsplit", since = "1.27.0")] +pub use core::slice::{RSplit, RSplitMut}; +#[stable(feature = "rust1", since = "1.0.0")] +pub use core::slice::{RSplitN, RSplitNMut, SplitN, SplitNMut}; +#[stable(feature = "split_inclusive", since = "1.51.0")] +pub use core::slice::{SplitInclusive, SplitInclusiveMut}; + +//////////////////////////////////////////////////////////////////////////////// +// Basic slice extension methods +//////////////////////////////////////////////////////////////////////////////// + +// HACK(japaric) needed for the implementation of `vec!` macro during testing +// N.B., see the `hack` module in this file for more details. +#[cfg(test)] +pub use hack::into_vec; + +// HACK(japaric) needed for the implementation of `Vec::clone` during testing +// N.B., see the `hack` module in this file for more details. +#[cfg(test)] +pub use 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 +pub(crate) mod hack { + use core::alloc::Allocator; + + use crate::boxed::Box; + use crate::vec::Vec; + + // We shouldn't add inline attribute to this since this is used in + // `vec!` macro mostly and causes perf regression. See #71204 for + // discussion and perf results. + pub fn into_vec<T, A: Allocator>(b: Box<[T], A>) -> Vec<T, A> { + unsafe { + let len = b.len(); + let (b, alloc) = Box::into_raw_with_allocator(b); + Vec::from_raw_parts_in(b as *mut T, len, len, alloc) + } + } + + #[cfg(not(no_global_oom_handling))] + #[inline] + pub fn to_vec<T: ConvertVec, A: Allocator>(s: &[T], alloc: A) -> Vec<T, A> { + T::to_vec(s, alloc) + } + + #[cfg(not(no_global_oom_handling))] + pub trait ConvertVec { + fn to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A> + where + Self: Sized; + } + + #[cfg(not(no_global_oom_handling))] + impl<T: Clone> ConvertVec for T { + #[inline] + default fn to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A> { + struct DropGuard<'a, T, A: Allocator> { + vec: &'a mut Vec<T, A>, + num_init: usize, + } + impl<'a, T, A: Allocator> Drop for DropGuard<'a, T, A> { + #[inline] + fn drop(&mut self) { + // SAFETY: + // items were marked initialized in the loop below + unsafe { + self.vec.set_len(self.num_init); + } + } + } + let mut vec = Vec::with_capacity_in(s.len(), alloc); + let mut guard = DropGuard { vec: &mut vec, num_init: 0 }; + let slots = guard.vec.spare_capacity_mut(); + // .take(slots.len()) is necessary for LLVM to remove bounds checks + // and has better codegen than zip. + for (i, b) in s.iter().enumerate().take(slots.len()) { + guard.num_init = i; + slots[i].write(b.clone()); + } + core::mem::forget(guard); + // SAFETY: + // the vec was allocated and initialized above to at least this length. + unsafe { + vec.set_len(s.len()); + } + vec + } + } + + #[cfg(not(no_global_oom_handling))] + impl<T: Copy> ConvertVec for T { + #[inline] + fn to_vec<A: Allocator>(s: &[Self], alloc: A) -> Vec<Self, A> { + let mut v = Vec::with_capacity_in(s.len(), alloc); + // SAFETY: + // allocated above with the capacity of `s`, and initialize to `s.len()` in + // ptr::copy_to_non_overlapping below. + unsafe { + s.as_ptr().copy_to_nonoverlapping(v.as_mut_ptr(), s.len()); + v.set_len(s.len()); + } + v + } + } +} + +#[cfg(not(test))] +impl<T> [T] { + /// Sorts the slice. + /// + /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) worst-case. + /// + /// When applicable, unstable sorting is preferred because it is generally faster than stable + /// sorting and it doesn't allocate auxiliary memory. + /// See [`sort_unstable`](slice::sort_unstable). + /// + /// # 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]); + /// ``` + #[cfg(not(no_global_oom_handling))] + #[rustc_allow_incoherent_impl] + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn sort(&mut self) + where + T: Ord, + { + merge_sort(self, |a, b| a.lt(b)); + } + + /// Sorts the slice with a comparator function. + /// + /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*)) worst-case. + /// + /// The comparator function must define a total ordering for the elements in the slice. If + /// the ordering is not total, the order of the elements is unspecified. An order is a + /// total order if it is (for all `a`, `b` and `c`): + /// + /// * total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true, and + /// * transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`. + /// + /// For example, while [`f64`] doesn't implement [`Ord`] because `NaN != NaN`, we can use + /// `partial_cmp` as our sort function when we know the slice doesn't contain a `NaN`. + /// + /// ``` + /// let mut floats = [5f64, 4.0, 1.0, 3.0, 2.0]; + /// floats.sort_by(|a, b| a.partial_cmp(b).unwrap()); + /// assert_eq!(floats, [1.0, 2.0, 3.0, 4.0, 5.0]); + /// ``` + /// + /// When applicable, unstable sorting is preferred because it is generally faster than stable + /// sorting and it doesn't allocate auxiliary memory. + /// See [`sort_unstable_by`](slice::sort_unstable_by). + /// + /// # 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]); + /// ``` + #[cfg(not(no_global_oom_handling))] + #[rustc_allow_incoherent_impl] + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn sort_by<F>(&mut self, mut compare: F) + where + F: FnMut(&T, &T) -> Ordering, + { + merge_sort(self, |a, b| compare(a, b) == Less); + } + + /// Sorts the slice with a key extraction function. + /// + /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* \* log(*n*)) + /// worst-case, where the key function is *O*(*m*). + /// + /// For expensive key functions (e.g. functions that are not simple property accesses or + /// basic operations), [`sort_by_cached_key`](slice::sort_by_cached_key) is likely to be + /// significantly faster, as it does not recompute element keys. + /// + /// When applicable, unstable sorting is preferred because it is generally faster than stable + /// sorting and it doesn't allocate auxiliary memory. + /// See [`sort_unstable_by_key`](slice::sort_unstable_by_key). + /// + /// # 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]); + /// ``` + #[cfg(not(no_global_oom_handling))] + #[rustc_allow_incoherent_impl] + #[stable(feature = "slice_sort_by_key", since = "1.7.0")] + #[inline] + pub fn sort_by_key<K, F>(&mut self, mut f: F) + where + F: FnMut(&T) -> K, + K: Ord, + { + merge_sort(self, |a, b| f(a).lt(&f(b))); + } + + /// Sorts the slice with a key extraction function. + /// + /// During sorting, the key function is called at most once per element, by using + /// temporary storage to remember the results of key evaluation. + /// The order of calls to the key function is unspecified and may change in future versions + /// of the standard library. + /// + /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* + *n* \* log(*n*)) + /// worst-case, where the key function is *O*(*m*). + /// + /// For simple key functions (e.g., functions that are property accesses or + /// basic operations), [`sort_by_key`](slice::sort_by_key) is likely to be + /// faster. + /// + /// # Current implementation + /// + /// The current algorithm is based on [pattern-defeating quicksort][pdqsort] by Orson Peters, + /// which combines the fast average case of randomized quicksort with the fast worst case of + /// heapsort, while achieving linear time on slices with certain patterns. It uses some + /// randomization to avoid degenerate cases, but with a fixed seed to always provide + /// deterministic behavior. + /// + /// In the worst case, the algorithm allocates temporary storage in a `Vec<(K, usize)>` the + /// length of the slice. + /// + /// # Examples + /// + /// ``` + /// let mut v = [-5i32, 4, 32, -3, 2]; + /// + /// v.sort_by_cached_key(|k| k.to_string()); + /// assert!(v == [-3, -5, 2, 32, 4]); + /// ``` + /// + /// [pdqsort]: https://github.com/orlp/pdqsort + #[cfg(not(no_global_oom_handling))] + #[rustc_allow_incoherent_impl] + #[stable(feature = "slice_sort_by_cached_key", since = "1.34.0")] + #[inline] + pub fn sort_by_cached_key<K, F>(&mut self, f: F) + where + F: FnMut(&T) -> K, + K: Ord, + { + // Helper macro for indexing our vector by the smallest possible type, to reduce allocation. + macro_rules! sort_by_key { + ($t:ty, $slice:ident, $f:ident) => {{ + let mut indices: Vec<_> = + $slice.iter().map($f).enumerate().map(|(i, k)| (k, i as $t)).collect(); + // The elements of `indices` are unique, as they are indexed, so any sort will be + // stable with respect to the original slice. We use `sort_unstable` here because + // it requires less memory allocation. + indices.sort_unstable(); + for i in 0..$slice.len() { + let mut index = indices[i].1; + while (index as usize) < i { + index = indices[index as usize].1; + } + indices[i].1 = index; + $slice.swap(i, index as usize); + } + }}; + } + + let sz_u8 = mem::size_of::<(K, u8)>(); + let sz_u16 = mem::size_of::<(K, u16)>(); + let sz_u32 = mem::size_of::<(K, u32)>(); + let sz_usize = mem::size_of::<(K, usize)>(); + + let len = self.len(); + if len < 2 { + return; + } + if sz_u8 < sz_u16 && len <= (u8::MAX as usize) { + return sort_by_key!(u8, self, f); + } + if sz_u16 < sz_u32 && len <= (u16::MAX as usize) { + return sort_by_key!(u16, self, f); + } + if sz_u32 < sz_usize && len <= (u32::MAX as usize) { + return sort_by_key!(u32, self, f); + } + sort_by_key!(usize, self, f) + } + + /// 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. + /// ``` + #[cfg(not(no_global_oom_handling))] + #[rustc_allow_incoherent_impl] + #[rustc_conversion_suggestion] + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn to_vec(&self) -> Vec<T> + where + T: Clone, + { + self.to_vec_in(Global) + } + + /// Copies `self` into a new `Vec` with an allocator. + /// + /// # Examples + /// + /// ``` + /// #![feature(allocator_api)] + /// + /// use std::alloc::System; + /// + /// let s = [10, 40, 30]; + /// let x = s.to_vec_in(System); + /// // Here, `s` and `x` can be modified independently. + /// ``` + #[cfg(not(no_global_oom_handling))] + #[rustc_allow_incoherent_impl] + #[inline] + #[unstable(feature = "allocator_api", issue = "32838")] + pub fn to_vec_in<A: Allocator>(&self, alloc: A) -> Vec<T, A> + where + T: Clone, + { + // N.B., see the `hack` module in this file for more details. + hack::to_vec(self, alloc) + } + + /// Converts `self` into a vector without clones or allocation. + /// + /// The resulting vector can be converted back into a box via + /// `Vec<T>`'s `into_boxed_slice` method. + /// + /// # 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]); + /// ``` + #[rustc_allow_incoherent_impl] + #[stable(feature = "rust1", since = "1.0.0")] + #[inline] + pub fn into_vec<A: Allocator>(self: Box<Self, A>) -> Vec<T, A> { + // N.B., see the `hack` module in this file for more details. + hack::into_vec(self) + } + + /// Creates a vector by repeating a slice `n` times. + /// + /// # Panics + /// + /// This function will panic if the capacity would overflow. + /// + /// # Examples + /// + /// Basic usage: + /// + /// ``` + /// assert_eq!([1, 2].repeat(3), vec![1, 2, 1, 2, 1, 2]); + /// ``` + /// + /// A panic upon overflow: + /// + /// ```should_panic + /// // this will panic at runtime + /// b"0123456789abcdef".repeat(usize::MAX); + /// ``` + #[rustc_allow_incoherent_impl] + #[cfg(not(no_global_oom_handling))] + #[stable(feature = "repeat_generic_slice", since = "1.40.0")] + pub fn repeat(&self, n: usize) -> Vec<T> + where + T: Copy, + { + if n == 0 { + return Vec::new(); + } + + // If `n` is larger than zero, it can be split as + // `n = 2^expn + rem (2^expn > rem, expn >= 0, rem >= 0)`. + // `2^expn` is the number represented by the leftmost '1' bit of `n`, + // and `rem` is the remaining part of `n`. + + // Using `Vec` to access `set_len()`. + let capacity = self.len().checked_mul(n).expect("capacity overflow"); + let mut buf = Vec::with_capacity(capacity); + + // `2^expn` repetition is done by doubling `buf` `expn`-times. + buf.extend(self); + { + let mut m = n >> 1; + // If `m > 0`, there are remaining bits up to the leftmost '1'. + while m > 0 { + // `buf.extend(buf)`: + unsafe { + ptr::copy_nonoverlapping( + buf.as_ptr(), + (buf.as_mut_ptr() as *mut T).add(buf.len()), + buf.len(), + ); + // `buf` has capacity of `self.len() * n`. + let buf_len = buf.len(); + buf.set_len(buf_len * 2); + } + + m >>= 1; + } + } + + // `rem` (`= n - 2^expn`) repetition is done by copying + // first `rem` repetitions from `buf` itself. + let rem_len = capacity - buf.len(); // `self.len() * rem` + if rem_len > 0 { + // `buf.extend(buf[0 .. rem_len])`: + unsafe { + // This is non-overlapping since `2^expn > rem`. + ptr::copy_nonoverlapping( + buf.as_ptr(), + (buf.as_mut_ptr() as *mut T).add(buf.len()), + rem_len, + ); + // `buf.len() + rem_len` equals to `buf.capacity()` (`= self.len() * n`). + buf.set_len(capacity); + } + } + buf + } + + /// Flattens a slice of `T` into a single value `Self::Output`. + /// + /// # Examples + /// + /// ``` + /// assert_eq!(["hello", "world"].concat(), "helloworld"); + /// assert_eq!([[1, 2], [3, 4]].concat(), [1, 2, 3, 4]); + /// ``` + #[rustc_allow_incoherent_impl] + #[stable(feature = "rust1", since = "1.0.0")] + pub fn concat<Item: ?Sized>(&self) -> <Self as Concat<Item>>::Output + where + Self: Concat<Item>, + { + Concat::concat(self) + } + + /// 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"); + /// assert_eq!([[1, 2], [3, 4]].join(&0), [1, 2, 0, 3, 4]); + /// assert_eq!([[1, 2], [3, 4]].join(&[0, 0][..]), [1, 2, 0, 0, 3, 4]); + /// ``` + #[rustc_allow_incoherent_impl] + #[stable(feature = "rename_connect_to_join", since = "1.3.0")] + pub fn join<Separator>(&self, sep: Separator) -> <Self as Join<Separator>>::Output + where + Self: Join<Separator>, + { + Join::join(self, sep) + } + + /// Flattens a slice of `T` into a single value `Self::Output`, placing a + /// given separator between each. + /// + /// # Examples + /// + /// ``` + /// # #![allow(deprecated)] + /// assert_eq!(["hello", "world"].connect(" "), "hello world"); + /// assert_eq!([[1, 2], [3, 4]].connect(&0), [1, 2, 0, 3, 4]); + /// ``` + #[rustc_allow_incoherent_impl] + #[stable(feature = "rust1", since = "1.0.0")] + #[deprecated(since = "1.3.0", note = "renamed to join")] + pub fn connect<Separator>(&self, sep: Separator) -> <Self as Join<Separator>>::Output + where + Self: Join<Separator>, + { + Join::join(self, sep) + } +} + +#[cfg(not(test))] +impl [u8] { + /// Returns a vector containing a copy of this slice where each byte + /// is mapped to its ASCII upper case equivalent. + /// + /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z', + /// but non-ASCII letters are unchanged. + /// + /// To uppercase the value in-place, use [`make_ascii_uppercase`]. + /// + /// [`make_ascii_uppercase`]: slice::make_ascii_uppercase + #[cfg(not(no_global_oom_handling))] + #[rustc_allow_incoherent_impl] + #[must_use = "this returns the uppercase bytes as a new Vec, \ + without modifying the original"] + #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")] + #[inline] + pub fn to_ascii_uppercase(&self) -> Vec<u8> { + let mut me = self.to_vec(); + me.make_ascii_uppercase(); + me + } + + /// Returns a vector containing a copy of this slice where each byte + /// is mapped to its ASCII lower case equivalent. + /// + /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z', + /// but non-ASCII letters are unchanged. + /// + /// To lowercase the value in-place, use [`make_ascii_lowercase`]. + /// + /// [`make_ascii_lowercase`]: slice::make_ascii_lowercase + #[cfg(not(no_global_oom_handling))] + #[rustc_allow_incoherent_impl] + #[must_use = "this returns the lowercase bytes as a new Vec, \ + without modifying the original"] + #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")] + #[inline] + pub fn to_ascii_lowercase(&self) -> Vec<u8> { + let mut me = self.to_vec(); + me.make_ascii_lowercase(); + me + } +} + +//////////////////////////////////////////////////////////////////////////////// +// Extension traits for slices over specific kinds of data +//////////////////////////////////////////////////////////////////////////////// + +/// Helper trait for [`[T]::concat`](slice::concat). +/// +/// Note: the `Item` type parameter is not used in this trait, +/// but it allows impls to be more generic. +/// Without it, we get this error: +/// +/// ```error +/// error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predica +/// --> src/liballoc/slice.rs:608:6 +/// | +/// 608 | impl<T: Clone, V: Borrow<[T]>> Concat for [V] { +/// | ^ unconstrained type parameter +/// ``` +/// +/// This is because there could exist `V` types with multiple `Borrow<[_]>` impls, +/// such that multiple `T` types would apply: +/// +/// ``` +/// # #[allow(dead_code)] +/// pub struct Foo(Vec<u32>, Vec<String>); +/// +/// impl std::borrow::Borrow<[u32]> for Foo { +/// fn borrow(&self) -> &[u32] { &self.0 } +/// } +/// +/// impl std::borrow::Borrow<[String]> for Foo { +/// fn borrow(&self) -> &[String] { &self.1 } +/// } +/// ``` +#[unstable(feature = "slice_concat_trait", issue = "27747")] +pub trait Concat<Item: ?Sized> { + #[unstable(feature = "slice_concat_trait", issue = "27747")] + /// The resulting type after concatenation + type Output; + + /// Implementation of [`[T]::concat`](slice::concat) + #[unstable(feature = "slice_concat_trait", issue = "27747")] + fn concat(slice: &Self) -> Self::Output; +} + +/// Helper trait for [`[T]::join`](slice::join) +#[unstable(feature = "slice_concat_trait", issue = "27747")] +pub trait Join<Separator> { + #[unstable(feature = "slice_concat_trait", issue = "27747")] + /// The resulting type after concatenation + type Output; + + /// Implementation of [`[T]::join`](slice::join) + #[unstable(feature = "slice_concat_trait", issue = "27747")] + fn join(slice: &Self, sep: Separator) -> Self::Output; +} + +#[cfg(not(no_global_oom_handling))] +#[unstable(feature = "slice_concat_ext", issue = "27747")] +impl<T: Clone, V: Borrow<[T]>> Concat<T> for [V] { + type Output = Vec<T>; + + fn concat(slice: &Self) -> Vec<T> { + let size = slice.iter().map(|slice| slice.borrow().len()).sum(); + let mut result = Vec::with_capacity(size); + for v in slice { + result.extend_from_slice(v.borrow()) + } + result + } +} + +#[cfg(not(no_global_oom_handling))] +#[unstable(feature = "slice_concat_ext", issue = "27747")] +impl<T: Clone, V: Borrow<[T]>> Join<&T> for [V] { + type Output = Vec<T>; + + fn join(slice: &Self, sep: &T) -> Vec<T> { + let mut iter = slice.iter(); + let first = match iter.next() { + Some(first) => first, + None => return vec![], + }; + let size = slice.iter().map(|v| v.borrow().len()).sum::<usize>() + slice.len() - 1; + let mut result = Vec::with_capacity(size); + result.extend_from_slice(first.borrow()); + + for v in iter { + result.push(sep.clone()); + result.extend_from_slice(v.borrow()) + } + result + } +} + +#[cfg(not(no_global_oom_handling))] +#[unstable(feature = "slice_concat_ext", issue = "27747")] +impl<T: Clone, V: Borrow<[T]>> Join<&[T]> for [V] { + type Output = Vec<T>; + + fn join(slice: &Self, sep: &[T]) -> Vec<T> { + let mut iter = slice.iter(); + let first = match iter.next() { + Some(first) => first, + None => return vec![], + }; + let size = + slice.iter().map(|v| v.borrow().len()).sum::<usize>() + sep.len() * (slice.len() - 1); + let mut result = Vec::with_capacity(size); + result.extend_from_slice(first.borrow()); + + for v in iter { + result.extend_from_slice(sep); + result.extend_from_slice(v.borrow()) + } + result + } +} + +//////////////////////////////////////////////////////////////////////////////// +// 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[..] + } +} + +#[cfg(not(no_global_oom_handling))] +#[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() + } + + #[cfg(test)] + fn to_owned(&self) -> Vec<T> { + hack::to_vec(self, Global) + } + + fn clone_into(&self, target: &mut Vec<T>) { + // drop anything in target that will not be overwritten + target.truncate(self.len()); + + // target.len <= self.len due to the truncate above, so the + // slices here are always in-bounds. + let (init, tail) = self.split_at(target.len()); + + // reuse the contained values' allocations/resources. + target.clone_from_slice(init); + target.extend_from_slice(tail); + } +} + +//////////////////////////////////////////////////////////////////////////////// +// Sorting +//////////////////////////////////////////////////////////////////////////////// + +/// Inserts `v[0]` into pre-sorted sequence `v[1..]` so that whole `v[..]` becomes sorted. +/// +/// This is the integral subroutine of insertion sort. +#[cfg(not(no_global_oom_handling))] +fn insert_head<T, F>(v: &mut [T], is_less: &mut F) +where + F: FnMut(&T, &T) -> bool, +{ + if v.len() >= 2 && is_less(&v[1], &v[0]) { + 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 tmp = mem::ManuallyDrop::new(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 `is_less`. + // 2. Fills the remaining hole in `v` in the end. + // + // Panic safety: + // + // If `is_less` 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: &*tmp, dest: &mut v[1] }; + ptr::copy_nonoverlapping(&v[1], &mut v[0], 1); + + for i in 2..v.len() { + if !is_less(&v[i], &*tmp) { + 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`. + } + } + + // When dropped, copies from `src` into `dest`. + struct InsertionHole<T> { + src: *const 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. +#[cfg(not(no_global_oom_handling))] +unsafe fn merge<T, F>(v: &mut [T], mid: usize, buf: *mut T, is_less: &mut F) +where + F: FnMut(&T, &T) -> bool, +{ + let len = v.len(); + let v = v.as_mut_ptr(); + let (v_mid, v_end) = unsafe { (v.add(mid), v.add(len)) }; + + // 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 `is_less`. + // 2. Fills the remaining hole in `v` if the longer run gets consumed first. + // + // Panic safety: + // + // If `is_less` 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. + unsafe { + ptr::copy_nonoverlapping(v, buf, mid); + hole = MergeHole { start: buf, end: buf.add(mid), 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. + unsafe { + let to_copy = if is_less(&*right, &**left) { + 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. + unsafe { + ptr::copy_nonoverlapping(v_mid, buf, len - mid); + hole = MergeHole { start: buf, end: buf.add(len - mid), 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. + unsafe { + let to_copy = if is_less(&*right.offset(-1), &*left.offset(-1)) { + 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 = unsafe { ptr.offset(1) }; + old + } + + unsafe fn decrement_and_get<T>(ptr: &mut *mut T) -> *mut T { + *ptr = unsafe { 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, and these are pointers into a slice's elements. + unsafe { + let len = self.end.sub_ptr(self.start); + 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](https://github.com/python/cpython/blob/main/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. +#[cfg(not(no_global_oom_handling))] +fn merge_sort<T, F>(v: &mut [T], mut is_less: F) +where + F: FnMut(&T, &T) -> bool, +{ + // Slices of up to this length get sorted using insertion sort. + const MAX_INSERTION: usize = 20; + // Very short runs are extended using insertion sort to span at least this many elements. + const MIN_RUN: usize = 10; + + // Sorting has no meaningful behavior on zero-sized types. + if size_of::<T>() == 0 { + return; + } + + 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 is_less); + } + } + 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 + // `is_less` 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; + unsafe { + if is_less(v.get_unchecked(start + 1), v.get_unchecked(start)) { + while start > 0 && is_less(v.get_unchecked(start), v.get_unchecked(start - 1)) { + start -= 1; + } + v[start..end].reverse(); + } else { + while start > 0 && !is_less(v.get_unchecked(start), v.get_unchecked(start - 1)) + { + 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 is_less); + } + + // Push this run onto the stack. + runs.push(Run { 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 is_less, + ); + } + 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 its 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, + } +} |