/*!
Lower level primitive types that are useful in a variety of circumstances.
# Overview
This list represents the principle types in this module and briefly describes
when you might want to use them.
* [`PatternID`] - A type that represents the identifier of a regex pattern.
This is probably the most widely used type in this module (which is why it's
also re-exported in the crate root).
* [`StateID`] - A type the represents the identifier of a finite automaton
state. This is used for both NFAs and DFAs, with the notable exception of
the hybrid NFA/DFA. (The hybrid NFA/DFA uses a special purpose "lazy" state
identifier.)
* [`SmallIndex`] - The internal representation of both a `PatternID` and a
`StateID`. Its purpose is to serve as a type that can index memory without
being as big as a `usize` on 64-bit targets. The main idea behind this type
is that there are many things in regex engines that will, in practice, never
overflow a 32-bit integer. (For example, like the number of patterns in a regex
or the number of states in an NFA.) Thus, a `SmallIndex` can be used to index
memory without peppering `as` casts everywhere. Moreover, it forces callers
to handle errors in the case where, somehow, the value would otherwise overflow
either a 32-bit integer or a `usize` (e.g., on 16-bit targets).
* [`NonMaxUsize`] - Represents a `usize` that cannot be `usize::MAX`. As a
result, `Option<NonMaxUsize>` has the same size in memory as a `usize`. This
useful, for example, when representing the offsets of submatches since it
reduces memory usage by a factor of 2. It is a legal optimization since Rust
guarantees that slices never have a length that exceeds `isize::MAX`.
*/
use core::num::NonZeroUsize;
#[cfg(feature = "alloc")]
use alloc::vec::Vec;
use crate::util::int::{Usize, U16, U32, U64};
/// A `usize` that can never be `usize::MAX`.
///
/// This is similar to `core::num::NonZeroUsize`, but instead of not permitting
/// a zero value, this does not permit a max value.
///
/// This is useful in certain contexts where one wants to optimize the memory
/// usage of things that contain match offsets. Namely, since Rust slices
/// are guaranteed to never have a length exceeding `isize::MAX`, we can use
/// `usize::MAX` as a sentinel to indicate that no match was found. Indeed,
/// types like `Option<NonMaxUsize>` have exactly the same size in memory as a
/// `usize`.
///
/// This type is defined to be `repr(transparent)` for
/// `core::num::NonZeroUsize`, which is in turn defined to be
/// `repr(transparent)` for `usize`.
#[derive(Clone, Copy, Eq, Hash, PartialEq, PartialOrd, Ord)]
#[repr(transparent)]
pub struct NonMaxUsize(NonZeroUsize);
impl NonMaxUsize {
/// Create a new `NonMaxUsize` from the given value.
///
/// This returns `None` only when the given value is equal to `usize::MAX`.
#[inline]
pub fn new(value: usize) -> Option<NonMaxUsize> {
NonZeroUsize::new(value.wrapping_add(1)).map(NonMaxUsize)
}
/// Return the underlying `usize` value. The returned value is guaranteed
/// to not equal `usize::MAX`.
#[inline]
pub fn get(self) -> usize {
self.0.get().wrapping_sub(1)
}
}
// We provide our own Debug impl because seeing the internal repr can be quite
// surprising if you aren't expecting it. e.g., 'NonMaxUsize(5)' vs just '5'.
impl core::fmt::Debug for NonMaxUsize {
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
write!(f, "{:?}", self.get())
}
}
/// A type that represents a "small" index.
///
/// The main idea of this type is to provide something that can index memory,
/// but uses less memory than `usize` on 64-bit systems. Specifically, its
/// representation is always a `u32` and has `repr(transparent)` enabled. (So
/// it is safe to transmute between a `u32` and a `SmallIndex`.)
///
/// A small index is typically useful in cases where there is no practical way
/// that the index will overflow a 32-bit integer. A good example of this is
/// an NFA state. If you could somehow build an NFA with `2^30` states, its
/// memory usage would be exorbitant and its runtime execution would be so
/// slow as to be completely worthless. Therefore, this crate generally deems
/// it acceptable to return an error if it would otherwise build an NFA that
/// requires a slice longer than what a 32-bit integer can index. In exchange,
/// we can use 32-bit indices instead of 64-bit indices in various places.
///
/// This type ensures this by providing a constructor that will return an error
/// if its argument cannot fit into the type. This makes it much easier to
/// handle these sorts of boundary cases that are otherwise extremely subtle.
///
/// On all targets, this type guarantees that its value will fit in a `u32`,
/// `i32`, `usize` and an `isize`. This means that on 16-bit targets, for
/// example, this type's maximum value will never overflow an `isize`,
/// which means it will never overflow a `i16` even though its internal
/// representation is still a `u32`.
///
/// The purpose for making the type fit into even signed integer types like
/// `isize` is to guarantee that the difference between any two small indices
/// is itself also a small index. This is useful in certain contexts, e.g.,
/// for delta encoding.
///
/// # Other types
///
/// The following types wrap `SmallIndex` to provide a more focused use case:
///
/// * [`PatternID`] is for representing the identifiers of patterns.
/// * [`StateID`] is for representing the identifiers of states in finite
/// automata. It is used for both NFAs and DFAs.
///
/// # Representation
///
/// This type is always represented internally by a `u32` and is marked as
/// `repr(transparent)`. Thus, this type always has the same representation as
/// a `u32`. It is thus safe to transmute between a `u32` and a `SmallIndex`.
///
/// # Indexing
///
/// For convenience, callers may use a `SmallIndex` to index slices.
///
/// # Safety
///
/// While a `SmallIndex` is meant to guarantee that its value fits into `usize`
/// without using as much space as a `usize` on all targets, callers must
/// not rely on this property for safety. Callers may choose to rely on this
/// property for correctness however. For example, creating a `SmallIndex` with
/// an invalid value can be done in entirely safe code. This may in turn result
/// in panics or silent logical errors.
#[derive(
Clone, Copy, Debug, Default, Eq, Hash, PartialEq, PartialOrd, Ord,
)]
#[repr(transparent)]
pub struct SmallIndex(u32);
impl SmallIndex {
/// The maximum index value.
#[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
pub const MAX: SmallIndex =
// FIXME: Use as_usize() once const functions in traits are stable.
SmallIndex::new_unchecked(core::i32::MAX as usize - 1);
/// The maximum index value.
#[cfg(target_pointer_width = "16")]
pub const MAX: SmallIndex =
SmallIndex::new_unchecked(core::isize::MAX - 1);
/// The total number of values that can be represented as a small index.
pub const LIMIT: usize = SmallIndex::MAX.as_usize() + 1;
/// The zero index value.
pub const ZERO: SmallIndex = SmallIndex::new_unchecked(0);
/// The number of bytes that a single small index uses in memory.
pub const SIZE: usize = core::mem::size_of::<SmallIndex>();
/// Create a new small index.
///
/// If the given index exceeds [`SmallIndex::MAX`], then this returns
/// an error.
#[inline]
pub fn new(index: usize) -> Result<SmallIndex, SmallIndexError> {
SmallIndex::try_from(index)
}
/// Create a new small index without checking whether the given value
/// exceeds [`SmallIndex::MAX`].
///
/// Using this routine with an invalid index value will result in
/// unspecified behavior, but *not* undefined behavior. In particular, an
/// invalid index value is likely to cause panics or possibly even silent
/// logical errors.
///
/// Callers must never rely on a `SmallIndex` to be within a certain range
/// for memory safety.
#[inline]
pub const fn new_unchecked(index: usize) -> SmallIndex {
// FIXME: Use as_u32() once const functions in traits are stable.
SmallIndex(index as u32)
}
/// Like [`SmallIndex::new`], but panics if the given index is not valid.
#[inline]
pub fn must(index: usize) -> SmallIndex {
SmallIndex::new(index).expect("invalid small index")
}
/// Return this small index as a `usize`. This is guaranteed to never
/// overflow `usize`.
#[inline]
pub const fn as_usize(&self) -> usize {
// FIXME: Use as_usize() once const functions in traits are stable.
self.0 as usize
}
/// Return this small index as a `u64`. This is guaranteed to never
/// overflow.
#[inline]
pub const fn as_u64(&self) -> u64 {
// FIXME: Use u64::from() once const functions in traits are stable.
self.0 as u64
}
/// Return the internal `u32` of this small index. This is guaranteed to
/// never overflow `u32`.
#[inline]
pub const fn as_u32(&self) -> u32 {
self.0
}
/// Return the internal `u32` of this small index represented as an `i32`.
/// This is guaranteed to never overflow an `i32`.
#[inline]
pub const fn as_i32(&self) -> i32 {
// This is OK because we guarantee that our max value is <= i32::MAX.
self.0 as i32
}
/// Returns one more than this small index as a usize.
///
/// Since a small index has constraints on its maximum value, adding `1` to
/// it will always fit in a `usize`, `u32` and a `i32`.
#[inline]
pub fn one_more(&self) -> usize {
self.as_usize() + 1
}
/// Decode this small index from the bytes given using the native endian
/// byte order for the current target.
///
/// If the decoded integer is not representable as a small index for the
/// current target, then this returns an error.
#[inline]
pub fn from_ne_bytes(
bytes: [u8; 4],
) -> Result<SmallIndex, SmallIndexError> {
let id = u32::from_ne_bytes(bytes);
if id > SmallIndex::MAX.as_u32() {
return Err(SmallIndexError { attempted: u64::from(id) });
}
Ok(SmallIndex::new_unchecked(id.as_usize()))
}
/// Decode this small index from the bytes given using the native endian
/// byte order for the current target.
///
/// This is analogous to [`SmallIndex::new_unchecked`] in that is does not
/// check whether the decoded integer is representable as a small index.
#[inline]
pub fn from_ne_bytes_unchecked(bytes: [u8; 4]) -> SmallIndex {
SmallIndex::new_unchecked(u32::from_ne_bytes(bytes).as_usize())
}
/// Return the underlying small index integer as raw bytes in native endian
/// format.
#[inline]
pub fn to_ne_bytes(&self) -> [u8; 4] {
self.0.to_ne_bytes()
}
}
impl<T> core::ops::Index<SmallIndex> for [T] {
type Output = T;
#[inline]
fn index(&self, index: SmallIndex) -> &T {
&self[index.as_usize()]
}
}
impl<T> core::ops::IndexMut<SmallIndex> for [T] {
#[inline]
fn index_mut(&mut self, index: SmallIndex) -> &mut T {
&mut self[index.as_usize()]
}
}
#[cfg(feature = "alloc")]
impl<T> core::ops::Index<SmallIndex> for Vec<T> {
type Output = T;
#[inline]
fn index(&self, index: SmallIndex) -> &T {
&self[index.as_usize()]
}
}
#[cfg(feature = "alloc")]
impl<T> core::ops::IndexMut<SmallIndex> for Vec<T> {
#[inline]
fn index_mut(&mut self, index: SmallIndex) -> &mut T {
&mut self[index.as_usize()]
}
}
impl From<u8> for SmallIndex {
fn from(index: u8) -> SmallIndex {
SmallIndex::new_unchecked(usize::from(index))
}
}
impl TryFrom<u16> for SmallIndex {
type Error = SmallIndexError;
fn try_from(index: u16) -> Result<SmallIndex, SmallIndexError> {
if u32::from(index) > SmallIndex::MAX.as_u32() {
return Err(SmallIndexError { attempted: u64::from(index) });
}
Ok(SmallIndex::new_unchecked(index.as_usize()))
}
}
impl TryFrom<u32> for SmallIndex {
type Error = SmallIndexError;
fn try_from(index: u32) -> Result<SmallIndex, SmallIndexError> {
if index > SmallIndex::MAX.as_u32() {
return Err(SmallIndexError { attempted: u64::from(index) });
}
Ok(SmallIndex::new_unchecked(index.as_usize()))
}
}
impl TryFrom<u64> for SmallIndex {
type Error = SmallIndexError;
fn try_from(index: u64) -> Result<SmallIndex, SmallIndexError> {
if index > SmallIndex::MAX.as_u64() {
return Err(SmallIndexError { attempted: index });
}
Ok(SmallIndex::new_unchecked(index.as_usize()))
}
}
impl TryFrom<usize> for SmallIndex {
type Error = SmallIndexError;
fn try_from(index: usize) -> Result<SmallIndex, SmallIndexError> {
if index > SmallIndex::MAX.as_usize() {
return Err(SmallIndexError { attempted: index.as_u64() });
}
Ok(SmallIndex::new_unchecked(index))
}
}
#[cfg(test)]
impl quickcheck::Arbitrary for SmallIndex {
fn arbitrary(gen: &mut quickcheck::Gen) -> SmallIndex {
use core::cmp::max;
let id = max(i32::MIN + 1, i32::arbitrary(gen)).abs();
if id > SmallIndex::MAX.as_i32() {
SmallIndex::MAX
} else {
SmallIndex::new(usize::try_from(id).unwrap()).unwrap()
}
}
}
/// This error occurs when a small index could not be constructed.
///
/// This occurs when given an integer exceeding the maximum small index value.
///
/// When the `std` feature is enabled, this implements the `Error` trait.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct SmallIndexError {
attempted: u64,
}
impl SmallIndexError {
/// Returns the value that could not be converted to a small index.
pub fn attempted(&self) -> u64 {
self.attempted
}
}
#[cfg(feature = "std")]
impl std::error::Error for SmallIndexError {}
impl core::fmt::Display for SmallIndexError {
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
write!(
f,
"failed to create small index from {:?}, which exceeds {:?}",
self.attempted(),
SmallIndex::MAX,
)
}
}
#[derive(Clone, Debug)]
pub(crate) struct SmallIndexIter {
rng: core::ops::Range<usize>,
}
impl Iterator for SmallIndexIter {
type Item = SmallIndex;
fn next(&mut self) -> Option<SmallIndex> {
if self.rng.start >= self.rng.end {
return None;
}
let next_id = self.rng.start + 1;
let id = core::mem::replace(&mut self.rng.start, next_id);
// new_unchecked is OK since we asserted that the number of
// elements in this iterator will fit in an ID at construction.
Some(SmallIndex::new_unchecked(id))
}
}
macro_rules! index_type_impls {
($name:ident, $err:ident, $iter:ident, $withiter:ident) => {
impl $name {
/// The maximum value.
pub const MAX: $name = $name(SmallIndex::MAX);
/// The total number of values that can be represented.
pub const LIMIT: usize = SmallIndex::LIMIT;
/// The zero value.
pub const ZERO: $name = $name(SmallIndex::ZERO);
/// The number of bytes that a single value uses in memory.
pub const SIZE: usize = SmallIndex::SIZE;
/// Create a new value that is represented by a "small index."
///
/// If the given index exceeds the maximum allowed value, then this
/// returns an error.
#[inline]
pub fn new(value: usize) -> Result<$name, $err> {
SmallIndex::new(value).map($name).map_err($err)
}
/// Create a new value without checking whether the given argument
/// exceeds the maximum.
///
/// Using this routine with an invalid value will result in
/// unspecified behavior, but *not* undefined behavior. In
/// particular, an invalid ID value is likely to cause panics or
/// possibly even silent logical errors.
///
/// Callers must never rely on this type to be within a certain
/// range for memory safety.
#[inline]
pub const fn new_unchecked(value: usize) -> $name {
$name(SmallIndex::new_unchecked(value))
}
/// Like `new`, but panics if the given value is not valid.
#[inline]
pub fn must(value: usize) -> $name {
$name::new(value).expect(concat!(
"invalid ",
stringify!($name),
" value"
))
}
/// Return the internal value as a `usize`. This is guaranteed to
/// never overflow `usize`.
#[inline]
pub const fn as_usize(&self) -> usize {
self.0.as_usize()
}
/// Return the internal value as a `u64`. This is guaranteed to
/// never overflow.
#[inline]
pub const fn as_u64(&self) -> u64 {
self.0.as_u64()
}
/// Return the internal value as a `u32`. This is guaranteed to
/// never overflow `u32`.
#[inline]
pub const fn as_u32(&self) -> u32 {
self.0.as_u32()
}
/// Return the internal value as a i32`. This is guaranteed to
/// never overflow an `i32`.
#[inline]
pub const fn as_i32(&self) -> i32 {
self.0.as_i32()
}
/// Returns one more than this value as a usize.
///
/// Since values represented by a "small index" have constraints
/// on their maximum value, adding `1` to it will always fit in a
/// `usize`, `u32` and a `i32`.
#[inline]
pub fn one_more(&self) -> usize {
self.0.one_more()
}
/// Decode this value from the bytes given using the native endian
/// byte order for the current target.
///
/// If the decoded integer is not representable as a small index
/// for the current target, then this returns an error.
#[inline]
pub fn from_ne_bytes(bytes: [u8; 4]) -> Result<$name, $err> {
SmallIndex::from_ne_bytes(bytes).map($name).map_err($err)
}
/// Decode this value from the bytes given using the native endian
/// byte order for the current target.
///
/// This is analogous to `new_unchecked` in that is does not check
/// whether the decoded integer is representable as a small index.
#[inline]
pub fn from_ne_bytes_unchecked(bytes: [u8; 4]) -> $name {
$name(SmallIndex::from_ne_bytes_unchecked(bytes))
}
/// Return the underlying integer as raw bytes in native endian
/// format.
#[inline]
pub fn to_ne_bytes(&self) -> [u8; 4] {
self.0.to_ne_bytes()
}
/// Returns an iterator over all values from 0 up to and not
/// including the given length.
///
/// If the given length exceeds this type's limit, then this
/// panics.
pub(crate) fn iter(len: usize) -> $iter {
$iter::new(len)
}
}
// We write our own Debug impl so that we get things like PatternID(5)
// instead of PatternID(SmallIndex(5)).
impl core::fmt::Debug for $name {
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
f.debug_tuple(stringify!($name)).field(&self.as_u32()).finish()
}
}
impl<T> core::ops::Index<$name> for [T] {
type Output = T;
#[inline]
fn index(&self, index: $name) -> &T {
&self[index.as_usize()]
}
}
impl<T> core::ops::IndexMut<$name> for [T] {
#[inline]
fn index_mut(&mut self, index: $name) -> &mut T {
&mut self[index.as_usize()]
}
}
#[cfg(feature = "alloc")]
impl<T> core::ops::Index<$name> for Vec<T> {
type Output = T;
#[inline]
fn index(&self, index: $name) -> &T {
&self[index.as_usize()]
}
}
#[cfg(feature = "alloc")]
impl<T> core::ops::IndexMut<$name> for Vec<T> {
#[inline]
fn index_mut(&mut self, index: $name) -> &mut T {
&mut self[index.as_usize()]
}
}
impl From<u8> for $name {
fn from(value: u8) -> $name {
$name(SmallIndex::from(value))
}
}
impl TryFrom<u16> for $name {
type Error = $err;
fn try_from(value: u16) -> Result<$name, $err> {
SmallIndex::try_from(value).map($name).map_err($err)
}
}
impl TryFrom<u32> for $name {
type Error = $err;
fn try_from(value: u32) -> Result<$name, $err> {
SmallIndex::try_from(value).map($name).map_err($err)
}
}
impl TryFrom<u64> for $name {
type Error = $err;
fn try_from(value: u64) -> Result<$name, $err> {
SmallIndex::try_from(value).map($name).map_err($err)
}
}
impl TryFrom<usize> for $name {
type Error = $err;
fn try_from(value: usize) -> Result<$name, $err> {
SmallIndex::try_from(value).map($name).map_err($err)
}
}
#[cfg(test)]
impl quickcheck::Arbitrary for $name {
fn arbitrary(gen: &mut quickcheck::Gen) -> $name {
$name(SmallIndex::arbitrary(gen))
}
}
/// This error occurs when a value could not be constructed.
///
/// This occurs when given an integer exceeding the maximum allowed
/// value.
///
/// When the `std` feature is enabled, this implements the `Error`
/// trait.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct $err(SmallIndexError);
impl $err {
/// Returns the value that could not be converted to an ID.
pub fn attempted(&self) -> u64 {
self.0.attempted()
}
}
#[cfg(feature = "std")]
impl std::error::Error for $err {}
impl core::fmt::Display for $err {
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
write!(
f,
"failed to create {} from {:?}, which exceeds {:?}",
stringify!($name),
self.attempted(),
$name::MAX,
)
}
}
#[derive(Clone, Debug)]
pub(crate) struct $iter(SmallIndexIter);
impl $iter {
fn new(len: usize) -> $iter {
assert!(
len <= $name::LIMIT,
"cannot create iterator for {} when number of \
elements exceed {:?}",
stringify!($name),
$name::LIMIT,
);
$iter(SmallIndexIter { rng: 0..len })
}
}
impl Iterator for $iter {
type Item = $name;
fn next(&mut self) -> Option<$name> {
self.0.next().map($name)
}
}
/// An iterator adapter that is like std::iter::Enumerate, but attaches
/// small index values instead. It requires `ExactSizeIterator`. At
/// construction, it ensures that the index of each element in the
/// iterator is representable in the corresponding small index type.
#[derive(Clone, Debug)]
pub(crate) struct $withiter<I> {
it: I,
ids: $iter,
}
impl<I: Iterator + ExactSizeIterator> $withiter<I> {
fn new(it: I) -> $withiter<I> {
let ids = $name::iter(it.len());
$withiter { it, ids }
}
}
impl<I: Iterator + ExactSizeIterator> Iterator for $withiter<I> {
type Item = ($name, I::Item);
fn next(&mut self) -> Option<($name, I::Item)> {
let item = self.it.next()?;
// Number of elements in this iterator must match, according
// to contract of ExactSizeIterator.
let id = self.ids.next().unwrap();
Some((id, item))
}
}
};
}
/// The identifier of a regex pattern, represented by a [`SmallIndex`].
///
/// The identifier for a pattern corresponds to its relative position among
/// other patterns in a single finite state machine. Namely, when building
/// a multi-pattern regex engine, one must supply a sequence of patterns to
/// match. The position (starting at 0) of each pattern in that sequence
/// represents its identifier. This identifier is in turn used to identify and
/// report matches of that pattern in various APIs.
///
/// See the [`SmallIndex`] type for more information about what it means for
/// a pattern ID to be a "small index."
///
/// Note that this type is defined in the
/// [`util::primitives`](crate::util::primitives) module, but it is also
/// re-exported at the crate root due to how common it is.
#[derive(Clone, Copy, Default, Eq, Hash, PartialEq, PartialOrd, Ord)]
#[repr(transparent)]
pub struct PatternID(SmallIndex);
/// The identifier of a finite automaton state, represented by a
/// [`SmallIndex`].
///
/// Most regex engines in this crate are built on top of finite automata. Each
/// state in a finite automaton defines transitions from its state to another.
/// Those transitions point to other states via their identifiers, i.e., a
/// `StateID`. Since finite automata tend to contain many transitions, it is
/// much more memory efficient to define state IDs as small indices.
///
/// See the [`SmallIndex`] type for more information about what it means for
/// a state ID to be a "small index."
#[derive(Clone, Copy, Default, Eq, Hash, PartialEq, PartialOrd, Ord)]
#[repr(transparent)]
pub struct StateID(SmallIndex);
index_type_impls!(PatternID, PatternIDError, PatternIDIter, WithPatternIDIter);
index_type_impls!(StateID, StateIDError, StateIDIter, WithStateIDIter);
/// A utility trait that defines a couple of adapters for making it convenient
/// to access indices as "small index" types. We require ExactSizeIterator so
/// that iterator construction can do a single check to make sure the index of
/// each element is representable by its small index type.
pub(crate) trait IteratorIndexExt: Iterator {
fn with_pattern_ids(self) -> WithPatternIDIter<Self>
where
Self: Sized + ExactSizeIterator,
{
WithPatternIDIter::new(self)
}
fn with_state_ids(self) -> WithStateIDIter<Self>
where
Self: Sized + ExactSizeIterator,
{
WithStateIDIter::new(self)
}
}
impl<I: Iterator> IteratorIndexExt for I {}
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