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// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
use crate::ule::*;
use alloc::boxed::Box;
use alloc::format;
use alloc::string::String;
use alloc::vec::Vec;
use core::cmp::Ordering;
use core::convert::TryFrom;
use core::marker::PhantomData;
use core::ops::Range;
// Also used by owned.rs
pub(super) const LENGTH_WIDTH: usize = 4;
pub(super) const METADATA_WIDTH: usize = 0;
pub(super) const MAX_LENGTH: usize = u32::MAX as usize;
pub(super) const MAX_INDEX: usize = u32::MAX as usize;
/// This trait allows switching between different possible internal
/// representations of VarZeroVec.
///
/// Currently this crate supports two formats: [`Index16`] and [`Index32`],
/// with [`Index16`] being the default for all [`VarZeroVec`](super::VarZeroVec)
/// types unless explicitly specified otherwise.
///
/// Do not implement this trait, its internals may be changed in the future,
/// and all of its associated items are hidden from the docs.
#[allow(clippy::missing_safety_doc)] // no safety section for you, don't implement this trait period
pub unsafe trait VarZeroVecFormat: 'static + Sized {
#[doc(hidden)]
const INDEX_WIDTH: usize;
#[doc(hidden)]
const MAX_VALUE: u32;
/// This is always `RawBytesULE<Self::INDEX_WIDTH>` however
/// Rust does not currently support using associated constants in const
/// generics
#[doc(hidden)]
type RawBytes: ULE;
// various conversions because RawBytes is an associated constant now
#[doc(hidden)]
fn rawbytes_to_usize(raw: Self::RawBytes) -> usize;
#[doc(hidden)]
fn usize_to_rawbytes(u: usize) -> Self::RawBytes;
#[doc(hidden)]
fn rawbytes_from_byte_slice_unchecked_mut(bytes: &mut [u8]) -> &mut [Self::RawBytes];
}
/// This is a [`VarZeroVecFormat`] that stores u16s in the index array.
/// Will have a smaller data size, but it's more likely for larger arrays
/// to be unrepresentable (and error on construction)
///
/// This is the default index size used by all [`VarZeroVec`](super::VarZeroVec) types.
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
#[allow(clippy::exhaustive_structs)] // marker
pub struct Index16;
/// This is a [`VarZeroVecFormat`] that stores u32s in the index array.
/// Will have a larger data size, but will support large arrays without
/// problems.
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
#[allow(clippy::exhaustive_structs)] // marker
pub struct Index32;
unsafe impl VarZeroVecFormat for Index16 {
const INDEX_WIDTH: usize = 2;
const MAX_VALUE: u32 = u16::MAX as u32;
type RawBytes = RawBytesULE<2>;
#[inline]
fn rawbytes_to_usize(raw: Self::RawBytes) -> usize {
raw.as_unsigned_int() as usize
}
#[inline]
fn usize_to_rawbytes(u: usize) -> Self::RawBytes {
(u as u16).to_unaligned()
}
#[inline]
fn rawbytes_from_byte_slice_unchecked_mut(bytes: &mut [u8]) -> &mut [Self::RawBytes] {
Self::RawBytes::from_byte_slice_unchecked_mut(bytes)
}
}
unsafe impl VarZeroVecFormat for Index32 {
const INDEX_WIDTH: usize = 4;
const MAX_VALUE: u32 = u32::MAX;
type RawBytes = RawBytesULE<4>;
#[inline]
fn rawbytes_to_usize(raw: Self::RawBytes) -> usize {
raw.as_unsigned_int() as usize
}
#[inline]
fn usize_to_rawbytes(u: usize) -> Self::RawBytes {
(u as u32).to_unaligned()
}
#[inline]
fn rawbytes_from_byte_slice_unchecked_mut(bytes: &mut [u8]) -> &mut [Self::RawBytes] {
Self::RawBytes::from_byte_slice_unchecked_mut(bytes)
}
}
/// A more parsed version of `VarZeroSlice`. This type is where most of the VarZeroVec
/// internal representation code lies.
///
/// This is *basically* an `&'a [u8]` to a zero copy buffer, but split out into
/// the buffer components. Logically this is capable of behaving as
/// a `&'a [T::VarULE]`, but since `T::VarULE` is unsized that type does not actually
/// exist.
///
/// See [`VarZeroVecComponents::parse_byte_slice()`] for information on the internal invariants involved
#[derive(Debug)]
pub struct VarZeroVecComponents<'a, T: ?Sized, F> {
/// The number of elements
len: u32,
/// The list of indices into the `things` slice
indices: &'a [u8],
/// The contiguous list of `T::VarULE`s
things: &'a [u8],
/// The original slice this was constructed from
entire_slice: &'a [u8],
marker: PhantomData<(&'a T, F)>,
}
// #[derive()] won't work here since we do not want it to be
// bound on T: Copy
impl<'a, T: ?Sized, F> Copy for VarZeroVecComponents<'a, T, F> {}
impl<'a, T: ?Sized, F> Clone for VarZeroVecComponents<'a, T, F> {
fn clone(&self) -> Self {
*self
}
}
impl<'a, T: VarULE + ?Sized, F> Default for VarZeroVecComponents<'a, T, F> {
#[inline]
fn default() -> Self {
Self::new()
}
}
impl<'a, T: VarULE + ?Sized, F> VarZeroVecComponents<'a, T, F> {
#[inline]
pub fn new() -> Self {
Self {
len: 0,
indices: &[],
things: &[],
entire_slice: &[],
marker: PhantomData,
}
}
}
impl<'a, T: VarULE + ?Sized, F: VarZeroVecFormat> VarZeroVecComponents<'a, T, F> {
/// Construct a new VarZeroVecComponents, checking invariants about the overall buffer size:
///
/// - There must be either zero or at least four bytes (if four, this is the "length" parsed as a usize)
/// - There must be at least `4*length + 4` bytes total, to form the array `indices` of indices
/// - `indices[i]..indices[i+1]` must index into a valid section of
/// `things`, such that it parses to a `T::VarULE`
/// - `indices[len - 1]..things.len()` must index into a valid section of
/// `things`, such that it parses to a `T::VarULE`
#[inline]
pub fn parse_byte_slice(slice: &'a [u8]) -> Result<Self, ZeroVecError> {
// The empty VZV is special-cased to the empty slice
if slice.is_empty() {
return Ok(VarZeroVecComponents {
len: 0,
indices: &[],
things: &[],
entire_slice: slice,
marker: PhantomData,
});
}
let len_bytes = slice
.get(0..LENGTH_WIDTH)
.ok_or(ZeroVecError::VarZeroVecFormatError)?;
let len_ule = RawBytesULE::<LENGTH_WIDTH>::parse_byte_slice(len_bytes)
.map_err(|_| ZeroVecError::VarZeroVecFormatError)?;
let len = len_ule
.first()
.ok_or(ZeroVecError::VarZeroVecFormatError)?
.as_unsigned_int();
let indices_bytes = slice
.get(
LENGTH_WIDTH + METADATA_WIDTH
..LENGTH_WIDTH + METADATA_WIDTH + F::INDEX_WIDTH * (len as usize),
)
.ok_or(ZeroVecError::VarZeroVecFormatError)?;
let things = slice
.get(F::INDEX_WIDTH * (len as usize) + LENGTH_WIDTH + METADATA_WIDTH..)
.ok_or(ZeroVecError::VarZeroVecFormatError)?;
let borrowed = VarZeroVecComponents {
len,
indices: indices_bytes,
things,
entire_slice: slice,
marker: PhantomData,
};
borrowed.check_indices_and_things()?;
Ok(borrowed)
}
/// Construct a [`VarZeroVecComponents`] from a byte slice that has previously
/// successfully returned a [`VarZeroVecComponents`] when passed to
/// [`VarZeroVecComponents::parse_byte_slice()`]. Will return the same
/// object as one would get from calling [`VarZeroVecComponents::parse_byte_slice()`].
///
/// # Safety
/// The bytes must have previously successfully run through
/// [`VarZeroVecComponents::parse_byte_slice()`]
pub unsafe fn from_bytes_unchecked(slice: &'a [u8]) -> Self {
// The empty VZV is special-cased to the empty slice
if slice.is_empty() {
return VarZeroVecComponents {
len: 0,
indices: &[],
things: &[],
entire_slice: slice,
marker: PhantomData,
};
}
let len_bytes = slice.get_unchecked(0..LENGTH_WIDTH);
let len_ule = RawBytesULE::<LENGTH_WIDTH>::from_byte_slice_unchecked(len_bytes);
let len = len_ule.get_unchecked(0).as_unsigned_int();
let indices_bytes = slice.get_unchecked(
LENGTH_WIDTH + METADATA_WIDTH
..LENGTH_WIDTH + METADATA_WIDTH + F::INDEX_WIDTH * (len as usize),
);
let things =
slice.get_unchecked(LENGTH_WIDTH + METADATA_WIDTH + F::INDEX_WIDTH * (len as usize)..);
VarZeroVecComponents {
len,
indices: indices_bytes,
things,
entire_slice: slice,
marker: PhantomData,
}
}
/// Get the number of elements in this vector
#[inline]
pub fn len(self) -> usize {
self.len as usize
}
/// Returns `true` if the vector contains no elements.
#[inline]
pub fn is_empty(self) -> bool {
self.indices.is_empty()
}
/// Get the idx'th element out of this slice. Returns `None` if out of bounds.
#[inline]
pub fn get(self, idx: usize) -> Option<&'a T> {
if idx >= self.len() {
return None;
}
Some(unsafe { self.get_unchecked(idx) })
}
/// Get the idx'th element out of this slice. Does not bounds check.
///
/// Safety:
/// - `idx` must be in bounds (`idx < self.len()`)
#[inline]
pub(crate) unsafe fn get_unchecked(self, idx: usize) -> &'a T {
let range = self.get_things_range(idx);
let things_slice = self.things.get_unchecked(range);
T::from_byte_slice_unchecked(things_slice)
}
/// Get the range in `things` for the element at `idx`. Does not bounds check.
///
/// Safety:
/// - `idx` must be in bounds (`idx < self.len()`)
#[inline]
unsafe fn get_things_range(self, idx: usize) -> Range<usize> {
let start = F::rawbytes_to_usize(*self.indices_slice().get_unchecked(idx));
let end = if idx + 1 == self.len() {
self.things.len()
} else {
F::rawbytes_to_usize(*self.indices_slice().get_unchecked(idx + 1))
};
debug_assert!(start <= end);
start..end
}
/// Get the range in `entire_slice` for the element at `idx`. Does not bounds check.
///
/// Safety:
/// - `idx` must be in bounds (`idx < self.len()`)
#[inline]
pub(crate) unsafe fn get_range(self, idx: usize) -> Range<usize> {
let range = self.get_things_range(idx);
let offset = (self.things as *const [u8] as *const u8)
.offset_from(self.entire_slice as *const [u8] as *const u8)
as usize;
range.start + offset..range.end + offset
}
/// Check the internal invariants of VarZeroVecComponents:
///
/// - `indices[i]..indices[i+1]` must index into a valid section of
/// `things`, such that it parses to a `T::VarULE`
/// - `indices[len - 1]..things.len()` must index into a valid section of
/// `things`, such that it parses to a `T::VarULE`
/// - `indices` is monotonically increasing
///
/// This method is NOT allowed to call any other methods on VarZeroVecComponents since all other methods
/// assume that the slice has been passed through check_indices_and_things
#[inline]
#[allow(clippy::len_zero)] // more explicit to enforce safety invariants
fn check_indices_and_things(self) -> Result<(), ZeroVecError> {
assert_eq!(self.len(), self.indices_slice().len());
if self.len() == 0 {
if self.things.len() > 0 {
return Err(ZeroVecError::VarZeroVecFormatError);
} else {
return Ok(());
}
}
// Safety: i is in bounds (assertion above)
let mut start = F::rawbytes_to_usize(unsafe { *self.indices_slice().get_unchecked(0) });
if start != 0 {
return Err(ZeroVecError::VarZeroVecFormatError);
}
for i in 0..self.len() {
let end = if i == self.len() - 1 {
self.things.len()
} else {
// Safety: i+1 is in bounds (assertion above)
F::rawbytes_to_usize(unsafe { *self.indices_slice().get_unchecked(i + 1) })
};
if start > end {
return Err(ZeroVecError::VarZeroVecFormatError);
}
if end > self.things.len() {
return Err(ZeroVecError::VarZeroVecFormatError);
}
// Safety: start..end is a valid range in self.things
let bytes = unsafe { self.things.get_unchecked(start..end) };
T::parse_byte_slice(bytes)?;
start = end;
}
Ok(())
}
/// Create an iterator over the Ts contained in VarZeroVecComponents
#[inline]
pub fn iter(self) -> impl Iterator<Item = &'a T> {
self.indices_slice()
.iter()
.copied()
.map(F::rawbytes_to_usize)
.zip(
self.indices_slice()
.iter()
.copied()
.map(F::rawbytes_to_usize)
.skip(1)
.chain([self.things.len()]),
)
.map(move |(start, end)| unsafe { self.things.get_unchecked(start..end) })
.map(|bytes| unsafe { T::from_byte_slice_unchecked(bytes) })
}
pub fn to_vec(self) -> Vec<Box<T>> {
self.iter().map(T::to_boxed).collect()
}
#[inline]
fn indices_slice(&self) -> &'a [F::RawBytes] {
unsafe { F::RawBytes::from_byte_slice_unchecked(self.indices) }
}
// Dump a debuggable representation of this type
#[allow(unused)] // useful for debugging
pub(crate) fn dump(&self) -> String {
let indices = self
.indices_slice()
.iter()
.copied()
.map(F::rawbytes_to_usize)
.collect::<Vec<_>>();
format!("VarZeroVecComponents {{ indices: {indices:?} }}")
}
}
impl<'a, T, F> VarZeroVecComponents<'a, T, F>
where
T: VarULE,
T: ?Sized,
T: Ord,
F: VarZeroVecFormat,
{
/// Binary searches a sorted `VarZeroVecComponents<T>` for the given element. For more information, see
/// the primitive function [`binary_search`](slice::binary_search).
pub fn binary_search(&self, needle: &T) -> Result<usize, usize> {
self.binary_search_impl(|probe| probe.cmp(needle), self.indices_slice())
}
pub fn binary_search_in_range(
&self,
needle: &T,
range: Range<usize>,
) -> Option<Result<usize, usize>> {
let indices_slice = self.indices_slice().get(range)?;
Some(self.binary_search_impl(|probe| probe.cmp(needle), indices_slice))
}
}
impl<'a, T, F> VarZeroVecComponents<'a, T, F>
where
T: VarULE,
T: ?Sized,
F: VarZeroVecFormat,
{
/// Binary searches a sorted `VarZeroVecComponents<T>` for the given predicate. For more information, see
/// the primitive function [`binary_search_by`](slice::binary_search_by).
pub fn binary_search_by(&self, predicate: impl FnMut(&T) -> Ordering) -> Result<usize, usize> {
self.binary_search_impl(predicate, self.indices_slice())
}
pub fn binary_search_in_range_by(
&self,
predicate: impl FnMut(&T) -> Ordering,
range: Range<usize>,
) -> Option<Result<usize, usize>> {
let indices_slice = self.indices_slice().get(range)?;
Some(self.binary_search_impl(predicate, indices_slice))
}
/// Binary searches a sorted `VarZeroVecComponents<T>` with the given predicate. For more information, see
/// the primitive function [`binary_search`](slice::binary_search).
fn binary_search_impl(
&self,
mut predicate: impl FnMut(&T) -> Ordering,
indices_slice: &[F::RawBytes],
) -> Result<usize, usize> {
// This code is an absolute atrocity. This code is not a place of honor. This
// code is known to the State of California to cause cancer.
//
// Unfortunately, the stdlib's `binary_search*` functions can only operate on slices.
// We do not have a slice. We have something we can .get() and index on, but that is not
// a slice.
//
// The `binary_search*` functions also do not have a variant where they give you the element's
// index, which we could otherwise use to directly index `self`.
// We do have `self.indices`, but these are indices into a byte buffer, which cannot in
// isolation be used to recoup the logical index of the element they refer to.
//
// However, `binary_search_by()` provides references to the elements of the slice being iterated.
// Since the layout of Rust slices is well-defined, we can do pointer arithmetic on these references
// to obtain the index being used by the search.
//
// It's worth noting that the slice we choose to search is irrelevant, as long as it has the appropriate
// length. `self.indices` is defined to have length `self.len()`, so it is convenient to use
// here and does not require additional allocations.
//
// The alternative to doing this is to implement our own binary search. This is significantly less fun.
// Note: We always use zero_index relative to the whole indices array, even if we are
// only searching a subslice of it.
let zero_index = self.indices.as_ptr() as *const _ as usize;
indices_slice.binary_search_by(|probe: &_| {
// `self.indices` is a vec of unaligned F::INDEX_WIDTH values, so we divide by F::INDEX_WIDTH
// to get the actual index
let index = (probe as *const _ as usize - zero_index) / F::INDEX_WIDTH;
// safety: we know this is in bounds
let actual_probe = unsafe { self.get_unchecked(index) };
predicate(actual_probe)
})
}
}
/// Collects the bytes for a VarZeroSlice into a Vec.
pub fn get_serializable_bytes_non_empty<T, A, F>(elements: &[A]) -> Option<Vec<u8>>
where
T: VarULE + ?Sized,
A: EncodeAsVarULE<T>,
F: VarZeroVecFormat,
{
debug_assert!(!elements.is_empty());
let len = compute_serializable_len::<T, A, F>(elements)?;
debug_assert!(len >= LENGTH_WIDTH as u32);
let mut output: Vec<u8> = alloc::vec![0; len as usize];
write_serializable_bytes::<T, A, F>(elements, &mut output);
Some(output)
}
/// Writes the bytes for a VarZeroSlice into an output buffer.
///
/// Every byte in the buffer will be initialized after calling this function.
///
/// # Panics
///
/// Panics if the buffer is not exactly the correct length.
pub fn write_serializable_bytes<T, A, F>(elements: &[A], output: &mut [u8])
where
T: VarULE + ?Sized,
A: EncodeAsVarULE<T>,
F: VarZeroVecFormat,
{
assert!(elements.len() <= MAX_LENGTH);
let num_elements_bytes = elements.len().to_le_bytes();
#[allow(clippy::indexing_slicing)] // Function contract allows panicky behavior
output[0..LENGTH_WIDTH].copy_from_slice(&num_elements_bytes[0..LENGTH_WIDTH]);
// idx_offset = offset from the start of the buffer for the next index
let mut idx_offset: usize = LENGTH_WIDTH + METADATA_WIDTH;
// first_dat_offset = offset from the start of the buffer of the first data block
let first_dat_offset: usize = idx_offset + elements.len() * F::INDEX_WIDTH;
// dat_offset = offset from the start of the buffer of the next data block
let mut dat_offset: usize = first_dat_offset;
for element in elements.iter() {
let element_len = element.encode_var_ule_len();
let idx_limit = idx_offset + F::INDEX_WIDTH;
#[allow(clippy::indexing_slicing)] // Function contract allows panicky behavior
let idx_slice = &mut output[idx_offset..idx_limit];
// VZV expects data offsets to be stored relative to the first data block
let idx = dat_offset - first_dat_offset;
assert!(idx <= MAX_INDEX);
#[allow(clippy::indexing_slicing)] // this function is explicitly panicky
idx_slice.copy_from_slice(&idx.to_le_bytes()[..F::INDEX_WIDTH]);
let dat_limit = dat_offset + element_len;
#[allow(clippy::indexing_slicing)] // Function contract allows panicky behavior
let dat_slice = &mut output[dat_offset..dat_limit];
element.encode_var_ule_write(dat_slice);
debug_assert_eq!(T::validate_byte_slice(dat_slice), Ok(()));
idx_offset = idx_limit;
dat_offset = dat_limit;
}
debug_assert_eq!(
idx_offset,
LENGTH_WIDTH + METADATA_WIDTH + F::INDEX_WIDTH * elements.len()
);
assert_eq!(dat_offset, output.len());
}
pub fn compute_serializable_len<T, A, F>(elements: &[A]) -> Option<u32>
where
T: VarULE + ?Sized,
A: EncodeAsVarULE<T>,
F: VarZeroVecFormat,
{
let idx_len: u32 = u32::try_from(elements.len())
.ok()?
.checked_mul(F::INDEX_WIDTH as u32)?
.checked_add(LENGTH_WIDTH as u32)?
.checked_add(METADATA_WIDTH as u32)?;
let data_len: u32 = elements
.iter()
.map(|v| u32::try_from(v.encode_var_ule_len()).ok())
.try_fold(0u32, |s, v| s.checked_add(v?))?;
let ret = idx_len.checked_add(data_len);
if let Some(r) = ret {
if r >= F::MAX_VALUE {
return None;
}
}
ret
}