Source code
Revision control
Copy as Markdown
Other Tools
// 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 super::VarZeroVecFormatError;
use crate::ule::*;
use core::cmp::Ordering;
use core::convert::TryFrom;
use core::marker::PhantomData;
use core::mem;
use core::ops::Range;
/// This trait allows switching between different possible internal
/// representations of VarZeroVec.
///
/// Currently this crate supports three formats: [`Index8`], [`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.
pub trait VarZeroVecFormat: 'static + Sized {
/// The type to use for the indexing array
///
/// Safety: must be a ULE for which all byte sequences are allowed
#[doc(hidden)]
type Index: IntegerULE;
/// The type to use for the length segment
///
/// Safety: must be a ULE for which all byte sequences are allowed
#[doc(hidden)]
type Len: IntegerULE;
}
/// This trait represents various ULE types that can be used to represent an integer
///
/// Do not implement this trait, its internals may be changed in the future,
/// and all of its associated items are hidden from the docs.
#[doc(hidden)]
pub unsafe trait IntegerULE: ULE {
/// The error to show when unable to construct a vec
#[doc(hidden)]
const TOO_LARGE_ERROR: &'static str;
/// Safety: must be sizeof(self)
#[doc(hidden)]
const SIZE: usize;
/// Safety: must be maximum integral value represented here
#[doc(hidden)]
const MAX_VALUE: u32;
/// Safety: Must roundtrip with from_usize and represent the correct
/// integral value
#[doc(hidden)]
fn iule_to_usize(self) -> usize;
#[doc(hidden)]
fn iule_from_usize(x: usize) -> Option<Self>;
/// Safety: Should always convert a buffer into an array of Self with the correct length
#[doc(hidden)]
#[cfg(feature = "alloc")]
fn iule_from_bytes_unchecked_mut(bytes: &mut [u8]) -> &mut [Self];
}
/// This is a [`VarZeroVecFormat`] that stores u8s in the index array, and a u8 for a length.
///
/// Will have a smaller data size, but it's *extremely* likely for larger arrays
/// to be unrepresentable (and error on construction). Should probably be used
/// for known-small arrays, where all but the last field are known-small.
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
#[allow(clippy::exhaustive_structs)] // marker
pub struct Index8;
/// This is a [`VarZeroVecFormat`] that stores u16s in the index array, and a u16 for a length.
///
/// 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, and a u32 for a length.
/// 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;
impl VarZeroVecFormat for Index8 {
type Index = u8;
type Len = u8;
}
impl VarZeroVecFormat for Index16 {
type Index = RawBytesULE<2>;
type Len = RawBytesULE<2>;
}
impl VarZeroVecFormat for Index32 {
type Index = RawBytesULE<4>;
type Len = RawBytesULE<4>;
}
unsafe impl IntegerULE for u8 {
const TOO_LARGE_ERROR: &'static str = "Attempted to build VarZeroVec out of elements that \
cumulatively are larger than a u8 in size";
const SIZE: usize = mem::size_of::<Self>();
const MAX_VALUE: u32 = u8::MAX as u32;
#[inline]
fn iule_to_usize(self) -> usize {
self as usize
}
#[inline]
fn iule_from_usize(u: usize) -> Option<Self> {
u8::try_from(u).ok()
}
#[inline]
#[cfg(feature = "alloc")]
fn iule_from_bytes_unchecked_mut(bytes: &mut [u8]) -> &mut [Self] {
bytes
}
}
unsafe impl IntegerULE for RawBytesULE<2> {
const TOO_LARGE_ERROR: &'static str = "Attempted to build VarZeroVec out of elements that \
cumulatively are larger than a u16 in size";
const SIZE: usize = mem::size_of::<Self>();
const MAX_VALUE: u32 = u16::MAX as u32;
#[inline]
fn iule_to_usize(self) -> usize {
self.as_unsigned_int() as usize
}
#[inline]
fn iule_from_usize(u: usize) -> Option<Self> {
u16::try_from(u).ok().map(u16::to_unaligned)
}
#[inline]
#[cfg(feature = "alloc")]
fn iule_from_bytes_unchecked_mut(bytes: &mut [u8]) -> &mut [Self] {
Self::from_bytes_unchecked_mut(bytes)
}
}
unsafe impl IntegerULE for RawBytesULE<4> {
const TOO_LARGE_ERROR: &'static str = "Attempted to build VarZeroVec out of elements that \
cumulatively are larger than a u32 in size";
const SIZE: usize = mem::size_of::<Self>();
const MAX_VALUE: u32 = u32::MAX;
#[inline]
fn iule_to_usize(self) -> usize {
self.as_unsigned_int() as usize
}
#[inline]
fn iule_from_usize(u: usize) -> Option<Self> {
u32::try_from(u).ok().map(u32::to_unaligned)
}
#[inline]
#[cfg(feature = "alloc")]
fn iule_from_bytes_unchecked_mut(bytes: &mut [u8]) -> &mut [Self] {
Self::from_bytes_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_bytes()`] 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
/// Since the first element is always at things[0], the first element of the indices array is for the *second* element
indices: &'a [u8],
/// The contiguous list of `T::VarULE`s
things: &'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: &[],
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 - 1) + 4` bytes total, to form the array `indices` of indices
/// - `0..indices[0]` must index into a valid section of
/// `things` (the data after `indices`), such that it parses to a `T::VarULE`
/// - `indices[i - 1]..indices[i]` must index into a valid section of
/// `things` (the data after `indices`), such that it parses to a `T::VarULE`
/// - `indices[len - 2]..things.len()` must index into a valid section of
/// `things`, such that it parses to a `T::VarULE`
#[inline]
pub fn parse_bytes(slice: &'a [u8]) -> Result<Self, VarZeroVecFormatError> {
// The empty VZV is special-cased to the empty slice
if slice.is_empty() {
return Ok(VarZeroVecComponents {
len: 0,
indices: &[],
things: &[],
marker: PhantomData,
});
}
let len_bytes = slice
.get(0..F::Len::SIZE)
.ok_or(VarZeroVecFormatError::Metadata)?;
let len_ule =
F::Len::parse_bytes_to_slice(len_bytes).map_err(|_| VarZeroVecFormatError::Metadata)?;
let len = len_ule
.first()
.ok_or(VarZeroVecFormatError::Metadata)?
.iule_to_usize();
let rest = slice
.get(F::Len::SIZE..)
.ok_or(VarZeroVecFormatError::Metadata)?;
let len_u32 = u32::try_from(len).map_err(|_| VarZeroVecFormatError::Metadata);
// We pass down the rest of the invariants
Self::parse_bytes_with_length(len_u32?, rest)
}
/// Construct a new VarZeroVecComponents, checking invariants about the overall buffer size:
///
/// - There must be at least `4*len` bytes total, to form the array `indices` of indices.
/// - `indices[i]..indices[i+1]` must index into a valid section of
/// `things` (the data after `indices`), 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_bytes_with_length(
len: u32,
slice: &'a [u8],
) -> Result<Self, VarZeroVecFormatError> {
let len_minus_one = len.checked_sub(1);
// The empty VZV is special-cased to the empty slice
let Some(len_minus_one) = len_minus_one else {
return Ok(VarZeroVecComponents {
len: 0,
indices: &[],
things: &[],
marker: PhantomData,
});
};
// The indices array is one element shorter since the first index is always 0,
// so we use len_minus_one
let indices_bytes = slice
.get(..F::Index::SIZE * (len_minus_one as usize))
.ok_or(VarZeroVecFormatError::Metadata)?;
let things = slice
.get(F::Index::SIZE * (len_minus_one as usize)..)
.ok_or(VarZeroVecFormatError::Metadata)?;
let borrowed = VarZeroVecComponents {
len,
indices: indices_bytes,
things,
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_bytes()`]. Will return the same
/// object as one would get from calling [`VarZeroVecComponents::parse_bytes()`].
///
/// # Safety
/// The bytes must have previously successfully run through
/// [`VarZeroVecComponents::parse_bytes()`]
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: &[],
marker: PhantomData,
};
}
let (len_bytes, data_bytes) = unsafe { slice.split_at_unchecked(F::Len::SIZE) };
// Safety: F::Len allows all byte sequences
let len_ule = F::Len::slice_from_bytes_unchecked(len_bytes);
let len = len_ule.get_unchecked(0).iule_to_usize();
let len_u32 = len as u32;
// Safety: This method requires the bytes to have passed through `parse_bytes()`
// whereas we're calling something that asks for `parse_bytes_with_length()`.
// The two methods perform similar validation, with parse_bytes() validating an additional
// 4-byte `length` header.
Self::from_bytes_unchecked_with_length(len_u32, data_bytes)
}
/// Construct a [`VarZeroVecComponents`] from a byte slice that has previously
/// successfully returned a [`VarZeroVecComponents`] when passed to
/// [`VarZeroVecComponents::parse_bytes()`]. Will return the same
/// object as one would get from calling [`VarZeroVecComponents::parse_bytes()`].
///
/// # Safety
/// The len,bytes must have previously successfully run through
/// [`VarZeroVecComponents::parse_bytes_with_length()`]
pub unsafe fn from_bytes_unchecked_with_length(len: u32, slice: &'a [u8]) -> Self {
let len_minus_one = len.checked_sub(1);
// The empty VZV is special-cased to the empty slice
let Some(len_minus_one) = len_minus_one else {
return VarZeroVecComponents {
len: 0,
indices: &[],
things: &[],
marker: PhantomData,
};
};
// The indices array is one element shorter since the first index is always 0,
// so we use len_minus_one
let indices_bytes = slice.get_unchecked(..F::Index::SIZE * (len_minus_one as usize));
let things = slice.get_unchecked(F::Index::SIZE * (len_minus_one as usize)..);
VarZeroVecComponents {
len,
indices: indices_bytes,
things,
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.len == 0
}
/// 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_bytes_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]
pub(crate) unsafe fn get_things_range(self, idx: usize) -> Range<usize> {
let start = if let Some(idx_minus_one) = idx.checked_sub(1) {
self.indices_slice()
.get_unchecked(idx_minus_one)
.iule_to_usize()
} else {
0
};
let end = if idx + 1 == self.len() {
self.things.len()
} else {
self.indices_slice().get_unchecked(idx).iule_to_usize()
};
debug_assert!(start <= end);
start..end
}
/// Get the size, in bytes, of the indices array
pub(crate) unsafe fn get_indices_size(self) -> usize {
self.indices.len()
}
/// 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]
#[expect(clippy::len_zero)] // more explicit to enforce safety invariants
fn check_indices_and_things(self) -> Result<(), VarZeroVecFormatError> {
if self.len() == 0 {
if self.things.len() > 0 {
return Err(VarZeroVecFormatError::Metadata);
} else {
return Ok(());
}
}
let indices_slice = self.indices_slice();
assert_eq!(self.len(), indices_slice.len() + 1);
// Safety: i is in bounds (assertion above)
let mut start = 0;
for i in 0..self.len() {
// The indices array is offset by 1: indices[0] is the end of the first
// element and the start of the next, since the start of the first element
// is always things[0]. So to get the end we get element `i`.
let end = if let Some(end) = indices_slice.get(i) {
end.iule_to_usize()
} else {
// This only happens at i = self.len() - 1 = indices_slice.len() + 1 - 1
// = indices_slice.len(). This is the last `end`, which is always the size of
// `things` and thus never stored in the array
self.things.len()
};
if start > end {
return Err(VarZeroVecFormatError::Metadata);
}
if end > self.things.len() {
return Err(VarZeroVecFormatError::Metadata);
}
// Safety: start..end is a valid range in self.things
let bytes = unsafe { self.things.get_unchecked(start..end) };
T::parse_bytes(bytes).map_err(VarZeroVecFormatError::Values)?;
start = end;
}
Ok(())
}
/// Create an iterator over the Ts contained in VarZeroVecComponents
#[inline]
pub fn iter(self) -> VarZeroSliceIter<'a, T, F> {
VarZeroSliceIter::new(self)
}
#[cfg(feature = "alloc")]
pub fn to_vec(self) -> alloc::vec::Vec<alloc::boxed::Box<T>> {
self.iter().map(T::to_boxed).collect()
}
#[inline]
fn indices_slice(&self) -> &'a [F::Index] {
unsafe { F::Index::slice_from_bytes_unchecked(self.indices) }
}
// Dump a debuggable representation of this type
#[allow(unused)] // useful for debugging
#[cfg(feature = "alloc")]
pub(crate) fn dump(&self) -> alloc::string::String {
let indices = self
.indices_slice()
.iter()
.copied()
.map(IntegerULE::iule_to_usize)
.collect::<alloc::vec::Vec<_>>();
alloc::format!("VarZeroVecComponents {{ indices: {indices:?} }}")
}
}
/// An iterator over VarZeroSlice
#[derive(Debug)]
pub struct VarZeroSliceIter<'a, T: ?Sized, F = Index16> {
components: VarZeroVecComponents<'a, T, F>,
index: usize,
// Safety invariant: must be a valid index into the data segment of `components`, or an index at the end
// i.e. start_index <= components.things.len()
//
// It must be a valid index into the `things` array of components, coming from `components.indices_slice()`
start_index: usize,
}
impl<'a, T: VarULE + ?Sized, F: VarZeroVecFormat> VarZeroSliceIter<'a, T, F> {
fn new(c: VarZeroVecComponents<'a, T, F>) -> Self {
Self {
components: c,
index: 0,
// Invariant upheld, 0 is always a valid index-or-end
start_index: 0,
}
}
}
impl<'a, T: VarULE + ?Sized, F: VarZeroVecFormat> Iterator for VarZeroSliceIter<'a, T, F> {
type Item = &'a T;
fn next(&mut self) -> Option<Self::Item> {
// Note: the indices array doesn't contain 0 or len, we need to specially handle those edges. The 0 is handled
// by start_index, and the len is handled by the code for `end`.
if self.index >= self.components.len() {
return None;
}
// Invariant established: self.index is in bounds for self.components.len(),
// which means it is in bounds for self.components.indices_slice() since that has the same length
let end = if self.index + 1 == self.components.len() {
// We don't store the end index since it is computable, so the last element should use self.components.things.len()
self.components.things.len()
} else {
// Safety: self.index was known to be in bounds from the bounds check above.
unsafe {
self.components
.indices_slice()
.get_unchecked(self.index)
.iule_to_usize()
}
};
// Invariant established: end has the same invariant as self.start_index since it comes from indices_slice, which is guaranteed
// to only contain valid indexes
let item = unsafe {
// Safety: self.start_index and end both have in-range invariants, plus they are valid indices from indices_slice
// which means we can treat this data as a T
T::from_bytes_unchecked(self.components.things.get_unchecked(self.start_index..end))
};
self.index += 1;
// Invariant upheld: end has the same invariant as self.start_index
self.start_index = end;
Some(item)
}
fn size_hint(&self) -> (usize, Option<usize>) {
let remainder = self.components.len() - self.index;
(remainder, Some(remainder))
}
}
impl<'a, T: VarULE + ?Sized, F: VarZeroVecFormat> ExactSizeIterator for VarZeroSliceIter<'a, T, F> {
fn len(&self) -> usize {
self.components.len() - self.index
}
}
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_by(|probe| probe.cmp(needle))
}
pub fn binary_search_in_range(
&self,
needle: &T,
range: Range<usize>,
) -> Option<Result<usize, usize>> {
self.binary_search_in_range_by(|probe| probe.cmp(needle), range)
}
}
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> {
// Safety: 0 and len are in range
unsafe { self.binary_search_in_range_unchecked(predicate, 0..self.len()) }
}
// Binary search within a range.
// Values returned are relative to the range start!
pub fn binary_search_in_range_by(
&self,
predicate: impl FnMut(&T) -> Ordering,
range: Range<usize>,
) -> Option<Result<usize, usize>> {
if range.end > self.len() {
return None;
}
if range.end < range.start {
return None;
}
// Safety: We bounds checked above: end is in-bounds or len, and start is <= end
let range_absolute =
unsafe { self.binary_search_in_range_unchecked(predicate, range.clone()) };
// The values returned are relative to the range start
Some(
range_absolute
.map(|o| o - range.start)
.map_err(|e| e - range.start),
)
}
/// Safety: range must be in range for the slice (start <= len, end <= len, start <= end)
unsafe fn binary_search_in_range_unchecked(
&self,
mut predicate: impl FnMut(&T) -> Ordering,
range: Range<usize>,
) -> Result<usize, usize> {
// Function invariant: size is always end - start
let mut start = range.start;
let mut end = range.end;
let mut size;
// Loop invariant: 0 <= start < end <= len
// This invariant is initialized by the function safety invariants and the loop condition
while start < end {
size = end - start;
// This establishes mid < end (which implies mid < len)
// size is end - start. start + size is end (which is <= len).
// mid = start + size/2 will be less than end
let mid = start + size / 2;
// Safety: mid is < end <= len, so in-range
let cmp = predicate(self.get_unchecked(mid));
match cmp {
Ordering::Less => {
// This retains the loop invariant since it
// increments start, and we already have 0 <= start
// start < end is enforced by the loop condition
start = mid + 1;
}
Ordering::Greater => {
// mid < end, so this decreases end.
// This means end <= len is still true, and
// end > start is enforced by the loop condition
end = mid;
}
Ordering::Equal => return Ok(mid),
}
}
Err(start)
}
}
/// Collects the bytes for a VarZeroSlice into a Vec.
#[cfg(feature = "alloc")]
pub fn get_serializable_bytes_non_empty<T, A, F>(elements: &[A]) -> Option<alloc::vec::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 >= F::Len::SIZE as u32,
"Must have at least F::Len::SIZE bytes to hold the length of the vector"
);
let mut output = alloc::vec![0u8; len as usize];
write_serializable_bytes::<T, A, F>(elements, &mut output);
Some(output)
}
/// Writes the bytes for a VarZeroLengthlessSlice into an output buffer.
/// Usable for a VarZeroSlice if you first write the length bytes.
///
/// 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_without_length<T, A, F>(elements: &[A], output: &mut [u8])
where
T: VarULE + ?Sized,
A: EncodeAsVarULE<T>,
F: VarZeroVecFormat,
{
assert!(elements.len() <= F::Len::MAX_VALUE as usize);
if elements.is_empty() {
return;
}
// idx_offset = offset from the start of the buffer for the next index
let mut idx_offset: usize = 0;
// first_dat_offset = offset from the start of the buffer of the first data block
let first_dat_offset: usize = idx_offset + (elements.len() - 1) * F::Index::SIZE;
// dat_offset = offset from the start of the buffer of the next data block
let mut dat_offset: usize = first_dat_offset;
for (i, element) in elements.iter().enumerate() {
let element_len = element.encode_var_ule_len();
// The first index is always 0. We don't write it, or update the idx offset.
if i != 0 {
let idx_limit = idx_offset + F::Index::SIZE;
#[expect(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 <= F::Index::MAX_VALUE as usize);
#[expect(clippy::expect_used)] // this function is explicitly panicky
let bytes_to_write = F::Index::iule_from_usize(idx).expect(F::Index::TOO_LARGE_ERROR);
idx_slice.copy_from_slice(ULE::slice_as_bytes(&[bytes_to_write]));
idx_offset = idx_limit;
}
let dat_limit = dat_offset + element_len;
#[expect(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_bytes(dat_slice), Ok(()));
dat_offset = dat_limit;
}
debug_assert_eq!(idx_offset, F::Index::SIZE * (elements.len() - 1));
assert_eq!(dat_offset, output.len());
}
/// 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,
{
if elements.is_empty() {
return;
}
assert!(elements.len() <= F::Len::MAX_VALUE as usize);
#[expect(clippy::expect_used)] // This function is explicitly panicky
let num_elements_ule = F::Len::iule_from_usize(elements.len()).expect(F::Len::TOO_LARGE_ERROR);
#[expect(clippy::indexing_slicing)] // Function contract allows panicky behavior
output[0..F::Len::SIZE].copy_from_slice(ULE::slice_as_bytes(&[num_elements_ule]));
#[expect(clippy::indexing_slicing)] // Function contract allows panicky behavior
write_serializable_bytes_without_length::<T, A, F>(elements, &mut output[F::Len::SIZE..]);
}
pub fn compute_serializable_len_without_length<T, A, F>(elements: &[A]) -> Option<u32>
where
T: VarULE + ?Sized,
A: EncodeAsVarULE<T>,
F: VarZeroVecFormat,
{
let elements_len = elements.len();
let Some(elements_len_minus_one) = elements_len.checked_sub(1) else {
// Empty vec is optimized to an empty byte representation
return Some(0);
};
let idx_len: u32 = u32::try_from(elements_len_minus_one)
.ok()?
.checked_mul(F::Index::SIZE 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::Index::MAX_VALUE {
return None;
}
}
ret
}
pub fn compute_serializable_len<T, A, F>(elements: &[A]) -> Option<u32>
where
T: VarULE + ?Sized,
A: EncodeAsVarULE<T>,
F: VarZeroVecFormat,
{
compute_serializable_len_without_length::<T, A, F>(elements).map(|x| x + F::Len::SIZE as u32)
}