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Add OptionULE and OptionVarULE (#1736)
* Add OptionULE * tests * git add * add OptionVarULE * review comments * add KV impl for OptionVarULE * add test * clarify * fix * clip
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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 | ||
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ). | ||
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use super::*; | ||
use core::cmp::Ordering; | ||
use core::marker::PhantomData; | ||
use core::mem::{self, MaybeUninit}; | ||
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/// This type is the [`ULE`] type for `Option<U>` where `U` is a [`ULE`] type | ||
/// | ||
/// # Example | ||
/// | ||
/// ```rust | ||
/// use zerovec::ZeroVec; | ||
/// | ||
/// let z = ZeroVec::alloc_from_slice(&[Some('a'), Some('á'), Some('ø'), None, Some('ł')]); | ||
/// | ||
/// assert_eq!(z.get(2), Some(Some(('ø')))); | ||
/// assert_eq!(z.get(3), Some(None)); | ||
/// ``` | ||
// Invariants: | ||
// The MaybeUninit is zeroed when None (bool = false), | ||
// and is valid when Some (bool = true) | ||
#[repr(packed)] | ||
pub struct OptionULE<U>(bool, MaybeUninit<U>); | ||
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impl<U: Copy> OptionULE<U> { | ||
/// Obtain this as an Option<T> | ||
pub fn get(self) -> Option<U> { | ||
if self.0 { | ||
unsafe { | ||
// safety: self.0 is true so the MaybeUninit is valid | ||
Some(self.1.assume_init()) | ||
} | ||
} else { | ||
None | ||
} | ||
} | ||
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/// Construct an OptionULE<U> from an equivalent Option<T> | ||
pub fn new(opt: Option<U>) -> Self { | ||
if let Some(inner) = opt { | ||
Self(true, MaybeUninit::new(inner)) | ||
} else { | ||
Self(false, MaybeUninit::zeroed()) | ||
} | ||
} | ||
} | ||
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// Safety (based on the safety checklist on the ULE trait): | ||
// 1. OptionULE does not include any uninitialized or padding bytes. | ||
// (achieved by `#[repr(packed)]` on a struct containing only ULE fields, | ||
// in the context of this impl. The MaybeUninit is valid for all byte sequences, and we only generate | ||
/// zeroed or valid-T byte sequences to fill it) | ||
// 2. OptionULE is aligned to 1 byte. | ||
// (achieved by `#[repr(packed)]` on a struct containing only ULE fields, in the context of this impl) | ||
// 3. The impl of validate_byte_slice() returns an error if any byte is not valid. | ||
// 4. The impl of validate_byte_slice() returns an error if there are extra bytes. | ||
// 5. The other ULE methods use the default impl. | ||
// 6. OptionULE byte equality is semantic equality by relying on the ULE equality | ||
// invariant on the subfields | ||
unsafe impl<U: ULE> ULE for OptionULE<U> { | ||
fn validate_byte_slice(bytes: &[u8]) -> Result<(), ZeroVecError> { | ||
let size = mem::size_of::<Self>(); | ||
if bytes.len() % size != 0 { | ||
return Err(ZeroVecError::length::<Self>(bytes.len())); | ||
} | ||
for chunk in bytes.chunks(size) { | ||
#[allow(clippy::indexing_slicing)] // `chunk` will have enough bytes to fit Self | ||
match chunk[0] { | ||
// https://doc.rust-lang.org/reference/types/boolean.html | ||
// Rust booleans are always size 1, align 1 values with valid bit patterns 0x0 or 0x1 | ||
0 => { | ||
if !chunk[1..].iter().all(|x| *x == 0) { | ||
return Err(ZeroVecError::parse::<Self>()); | ||
} | ||
} | ||
1 => U::validate_byte_slice(&chunk[1..])?, | ||
_ => return Err(ZeroVecError::parse::<Self>()), | ||
} | ||
} | ||
Ok(()) | ||
} | ||
} | ||
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impl<T: AsULE> AsULE for Option<T> { | ||
type ULE = OptionULE<T::ULE>; | ||
fn to_unaligned(self) -> OptionULE<T::ULE> { | ||
OptionULE::new(self.map(T::to_unaligned)) | ||
} | ||
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fn from_unaligned(other: OptionULE<T::ULE>) -> Self { | ||
other.get().map(T::from_unaligned) | ||
} | ||
} | ||
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impl<U: Copy> Copy for OptionULE<U> {} | ||
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impl<U: Copy> Clone for OptionULE<U> { | ||
fn clone(&self) -> Self { | ||
*self | ||
} | ||
} | ||
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impl<U: Copy + PartialEq> PartialEq for OptionULE<U> { | ||
fn eq(&self, other: &Self) -> bool { | ||
self.get().eq(&other.get()) | ||
} | ||
} | ||
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impl<U: Copy + Eq> Eq for OptionULE<U> {} | ||
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/// A type allowing one to represent `Option<U>` for [`VarULE`] `U` types. | ||
/// | ||
/// ```rust | ||
/// use zerovec::VarZeroVec; | ||
/// use zerovec::ule::OptionVarULE; | ||
/// | ||
/// let mut zv: VarZeroVec<OptionVarULE<str>> = VarZeroVec::new(); | ||
/// | ||
/// zv.make_mut().push(&None::<&str>); | ||
/// zv.make_mut().push(&Some("hello")); | ||
/// zv.make_mut().push(&Some("world")); | ||
/// zv.make_mut().push(&None::<&str>); | ||
/// | ||
/// assert_eq!(zv.get(0).unwrap().as_ref(), None); | ||
/// assert_eq!(zv.get(1).unwrap().as_ref(), Some("hello")); | ||
/// ``` | ||
// The slice field is empty when None (bool = false), | ||
// and is a valid T when Some (bool = true) | ||
#[repr(packed)] | ||
pub struct OptionVarULE<U: VarULE + ?Sized>(PhantomData<U>, bool, [u8]); | ||
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impl<U: VarULE + ?Sized> OptionVarULE<U> { | ||
/// Obtain this as an `Option<&U>` | ||
pub fn as_ref(&self) -> Option<&U> { | ||
if self.1 { | ||
unsafe { | ||
// Safety: byte field is a valid T if boolean field is true | ||
Some(U::from_byte_slice_unchecked(&self.2)) | ||
} | ||
} else { | ||
None | ||
} | ||
} | ||
} | ||
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// Safety (based on the safety checklist on the VarULE trait): | ||
// 1. OptionVarULE<T> does not include any uninitialized or padding bytes | ||
// (achieved by being repr(packed) on ULE types) | ||
// 2. OptionVarULE<T> is aligned to 1 byte (achieved by being repr(packed) on ULE types) | ||
// 3. The impl of `validate_byte_slice()` returns an error if any byte is not valid. | ||
// 4. The impl of `validate_byte_slice()` returns an error if the slice cannot be used in its entirety | ||
// 5. The impl of `from_byte_slice_unchecked()` returns a reference to the same data. | ||
// 6. All other methods are defaulted | ||
// 7. OptionVarULE<T> byte equality is semantic equality (achieved by being an aggregate) | ||
unsafe impl<U: VarULE + ?Sized> VarULE for OptionVarULE<U> { | ||
#[inline] | ||
fn validate_byte_slice(slice: &[u8]) -> Result<(), ZeroVecError> { | ||
if slice.is_empty() { | ||
return Err(ZeroVecError::length::<Self>(slice.len())); | ||
} | ||
#[allow(clippy::indexing_slicing)] // slice already verified to be nonempty | ||
match slice[0] { | ||
// https://doc.rust-lang.org/reference/types/boolean.html | ||
// Rust booleans are always size 1, align 1 values with valid bit patterns 0x0 or 0x1 | ||
0 => { | ||
if slice.len() != 1 { | ||
Err(ZeroVecError::length::<Self>(slice.len())) | ||
} else { | ||
Ok(()) | ||
} | ||
} | ||
1 => U::validate_byte_slice(&slice[1..]), | ||
_ => Err(ZeroVecError::parse::<Self>()), | ||
} | ||
} | ||
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#[inline] | ||
unsafe fn from_byte_slice_unchecked(bytes: &[u8]) -> &Self { | ||
let metadata = bytes.len() - 1; | ||
let entire_struct_as_slice: *const [u8] = | ||
::core::slice::from_raw_parts(bytes.as_ptr(), metadata); | ||
&*(entire_struct_as_slice as *const Self) | ||
} | ||
} | ||
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unsafe impl<T, U> EncodeAsVarULE<OptionVarULE<U>> for Option<T> | ||
where | ||
T: EncodeAsVarULE<U>, | ||
U: VarULE + ?Sized, | ||
{ | ||
fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R { | ||
// unnecessary if the other two are implemented | ||
unreachable!() | ||
} | ||
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#[inline] | ||
fn encode_var_ule_len(&self) -> usize { | ||
if let Some(ref inner) = *self { | ||
// slice + boolean | ||
1 + inner.encode_var_ule_len() | ||
} else { | ||
// boolean + empty slice | ||
1 | ||
} | ||
} | ||
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#[allow(clippy::indexing_slicing)] // This method is allowed to panic when lengths are invalid | ||
fn encode_var_ule_write(&self, dst: &mut [u8]) { | ||
if let Some(ref inner) = *self { | ||
debug_assert!( | ||
!dst.is_empty(), | ||
"OptionVarULE must have at least one byte when Some" | ||
); | ||
dst[0] = 1; | ||
inner.encode_var_ule_write(&mut dst[1..]); | ||
} else { | ||
debug_assert!( | ||
dst.len() == 1, | ||
"OptionVarULE must have exactly one byte when None" | ||
); | ||
dst[0] = 0; | ||
} | ||
} | ||
} | ||
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impl<U: VarULE + ?Sized + PartialEq> PartialEq for OptionVarULE<U> { | ||
fn eq(&self, other: &Self) -> bool { | ||
self.as_ref().eq(&other.as_ref()) | ||
} | ||
} | ||
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impl<U: VarULE + ?Sized + Eq> Eq for OptionVarULE<U> {} | ||
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impl<U: VarULE + ?Sized + PartialOrd> PartialOrd for OptionVarULE<U> { | ||
fn partial_cmp(&self, other: &Self) -> Option<Ordering> { | ||
self.as_ref().partial_cmp(&other.as_ref()) | ||
} | ||
} | ||
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impl<U: VarULE + ?Sized + Ord> Ord for OptionVarULE<U> { | ||
fn cmp(&self, other: &Self) -> Ordering { | ||
self.as_ref().cmp(&other.as_ref()) | ||
} | ||
} |