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use core::{cmp, fmt, mem, u16, usize};
use alloc::{string::String, vec, vec::Vec};
use crate::packed::api::MatchKind;
/// The type used for representing a pattern identifier.
///
/// We don't use `usize` here because our packed searchers don't scale to
/// huge numbers of patterns, so we keep things a bit smaller.
pub type PatternID = u16;
/// A non-empty collection of non-empty patterns to search for.
///
/// This collection of patterns is what is passed around to both execute
/// searches and to construct the searchers themselves. Namely, this permits
/// searches to avoid copying all of the patterns, and allows us to keep only
/// one copy throughout all packed searchers.
///
/// Note that this collection is not a set. The same pattern can appear more
/// than once.
#[derive(Clone, Debug)]
pub struct Patterns {
/// The match semantics supported by this collection of patterns.
///
/// The match semantics determines the order of the iterator over patterns.
/// For leftmost-first, patterns are provided in the same order as were
/// provided by the caller. For leftmost-longest, patterns are provided in
/// descending order of length, with ties broken by the order in which they
/// were provided by the caller.
kind: MatchKind,
/// The collection of patterns, indexed by their identifier.
by_id: Vec<Vec<u8>>,
/// The order of patterns defined for iteration, given by pattern
/// identifiers. The order of `by_id` and `order` is always the same for
/// leftmost-first semantics, but may be different for leftmost-longest
/// semantics.
order: Vec<PatternID>,
/// The length of the smallest pattern, in bytes.
minimum_len: usize,
/// The largest pattern identifier. This should always be equivalent to
/// the number of patterns minus one in this collection.
max_pattern_id: PatternID,
/// The total number of pattern bytes across the entire collection. This
/// is used for reporting total heap usage in constant time.
total_pattern_bytes: usize,
}
impl Patterns {
/// Create a new collection of patterns for the given match semantics. The
/// ID of each pattern is the index of the pattern at which it occurs in
/// the `by_id` slice.
///
/// If any of the patterns in the slice given are empty, then this panics.
/// Similarly, if the number of patterns given is zero, then this also
/// panics.
pub fn new() -> Patterns {
Patterns {
kind: MatchKind::default(),
by_id: vec![],
order: vec![],
minimum_len: usize::MAX,
max_pattern_id: 0,
total_pattern_bytes: 0,
}
}
/// Add a pattern to this collection.
///
/// This panics if the pattern given is empty.
pub fn add(&mut self, bytes: &[u8]) {
assert!(!bytes.is_empty());
assert!(self.by_id.len() <= u16::MAX as usize);
let id = self.by_id.len() as u16;
self.max_pattern_id = id;
self.order.push(id);
self.by_id.push(bytes.to_vec());
self.minimum_len = cmp::min(self.minimum_len, bytes.len());
self.total_pattern_bytes += bytes.len();
}
/// Set the match kind semantics for this collection of patterns.
///
/// If the kind is not set, then the default is leftmost-first.
pub fn set_match_kind(&mut self, kind: MatchKind) {
self.kind = kind;
match self.kind {
MatchKind::LeftmostFirst => {
self.order.sort();
}
MatchKind::LeftmostLongest => {
let (order, by_id) = (&mut self.order, &mut self.by_id);
order.sort_by(|&id1, &id2| {
by_id[id1 as usize]
.len()
.cmp(&by_id[id2 as usize].len())
.reverse()
});
}
}
}
/// Return the number of patterns in this collection.
///
/// This is guaranteed to be greater than zero.
pub fn len(&self) -> usize {
self.by_id.len()
}
/// Returns true if and only if this collection of patterns is empty.
pub fn is_empty(&self) -> bool {
self.len() == 0
}
/// Returns the approximate total amount of heap used by these patterns, in
/// units of bytes.
pub fn memory_usage(&self) -> usize {
self.order.len() * mem::size_of::<PatternID>()
+ self.by_id.len() * mem::size_of::<Vec<u8>>()
+ self.total_pattern_bytes
}
/// Clears all heap memory associated with this collection of patterns and
/// resets all state such that it is a valid empty collection.
pub fn reset(&mut self) {
self.kind = MatchKind::default();
self.by_id.clear();
self.order.clear();
self.minimum_len = usize::MAX;
self.max_pattern_id = 0;
}
/// Return the maximum pattern identifier in this collection. This can be
/// useful in searchers for ensuring that the collection of patterns they
/// are provided at search time and at build time have the same size.
pub fn max_pattern_id(&self) -> PatternID {
assert_eq!((self.max_pattern_id + 1) as usize, self.len());
self.max_pattern_id
}
/// Returns the length, in bytes, of the smallest pattern.
///
/// This is guaranteed to be at least one.
pub fn minimum_len(&self) -> usize {
self.minimum_len
}
/// Returns the match semantics used by these patterns.
pub fn match_kind(&self) -> &MatchKind {
&self.kind
}
/// Return the pattern with the given identifier. If such a pattern does
/// not exist, then this panics.
pub fn get(&self, id: PatternID) -> Pattern<'_> {
Pattern(&self.by_id[id as usize])
}
/// Return the pattern with the given identifier without performing bounds
/// checks.
///
/// # Safety
///
/// Callers must ensure that a pattern with the given identifier exists
/// before using this method.
#[cfg(all(feature = "std", target_arch = "x86_64"))]
pub unsafe fn get_unchecked(&self, id: PatternID) -> Pattern<'_> {
Pattern(self.by_id.get_unchecked(id as usize))
}
/// Return an iterator over all the patterns in this collection, in the
/// order in which they should be matched.
///
/// Specifically, in a naive multi-pattern matcher, the following is
/// guaranteed to satisfy the match semantics of this collection of
/// patterns:
///
/// ```ignore
/// for i in 0..haystack.len():
/// for p in patterns.iter():
/// if haystack[i..].starts_with(p.bytes()):
/// return Match(p.id(), i, i + p.bytes().len())
/// ```
///
/// Namely, among the patterns in a collection, if they are matched in
/// the order provided by this iterator, then the result is guaranteed
/// to satisfy the correct match semantics. (Either leftmost-first or
/// leftmost-longest.)
pub fn iter(&self) -> PatternIter<'_> {
PatternIter { patterns: self, i: 0 }
}
}
/// An iterator over the patterns in the `Patterns` collection.
///
/// The order of the patterns provided by this iterator is consistent with the
/// match semantics of the originating collection of patterns.
///
/// The lifetime `'p` corresponds to the lifetime of the collection of patterns
/// this is iterating over.
#[derive(Debug)]
pub struct PatternIter<'p> {
patterns: &'p Patterns,
i: usize,
}
impl<'p> Iterator for PatternIter<'p> {
type Item = (PatternID, Pattern<'p>);
fn next(&mut self) -> Option<(PatternID, Pattern<'p>)> {
if self.i >= self.patterns.len() {
return None;
}
let id = self.patterns.order[self.i];
let p = self.patterns.get(id);
self.i += 1;
Some((id, p))
}
}
/// A pattern that is used in packed searching.
#[derive(Clone)]
pub struct Pattern<'a>(&'a [u8]);
impl<'a> fmt::Debug for Pattern<'a> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Pattern")
.field("lit", &String::from_utf8_lossy(&self.0))
.finish()
}
}
impl<'p> Pattern<'p> {
/// Returns the length of this pattern, in bytes.
pub fn len(&self) -> usize {
self.0.len()
}
/// Returns the bytes of this pattern.
pub fn bytes(&self) -> &[u8] {
&self.0
}
/// Returns the first `len` low nybbles from this pattern. If this pattern
/// is shorter than `len`, then this panics.
#[cfg(all(feature = "std", target_arch = "x86_64"))]
pub fn low_nybbles(&self, len: usize) -> Vec<u8> {
let mut nybs = vec![];
for &b in self.bytes().iter().take(len) {
nybs.push(b & 0xF);
}
nybs
}
/// Returns true if this pattern is a prefix of the given bytes.
#[inline(always)]
pub fn is_prefix(&self, bytes: &[u8]) -> bool {
self.len() <= bytes.len() && self.equals(&bytes[..self.len()])
}
/// Returns true if and only if this pattern equals the given bytes.
#[inline(always)]
pub fn equals(&self, bytes: &[u8]) -> bool {
// Why not just use memcmp for this? Well, memcmp requires calling out
// to libc, and this routine is called in fairly hot code paths. Other
// than just calling out to libc, it also seems to result in worse
// codegen. By rolling our own memcpy in pure Rust, it seems to appear
// more friendly to the optimizer.
//
// This results in an improvement in just about every benchmark. Some
// smaller than others, but in some cases, up to 30% faster.
let (x, y) = (self.bytes(), bytes);
if x.len() != y.len() {
return false;
}
// If we don't have enough bytes to do 4-byte at a time loads, then
// fall back to the naive slow version.
if x.len() < 4 {
for (&b1, &b2) in x.iter().zip(y) {
if b1 != b2 {
return false;
}
}
return true;
}
// When we have 4 or more bytes to compare, then proceed in chunks of 4
// at a time using unaligned loads.
//
// Also, why do 4 byte loads instead of, say, 8 byte loads? The reason
// is that this particular version of memcmp is likely to be called
// with tiny needles. That means that if we do 8 byte loads, then a
// higher proportion of memcmp calls will use the slower variant above.
// With that said, this is a hypothesis and is only loosely supported
// by benchmarks. There's likely some improvement that could be made
// here. The main thing here though is to optimize for latency, not
// throughput.
// SAFETY: Via the conditional above, we know that both `px` and `py`
// have the same length, so `px < pxend` implies that `py < pyend`.
// Thus, derefencing both `px` and `py` in the loop below is safe.
//
// Moreover, we set `pxend` and `pyend` to be 4 bytes before the actual
// end of of `px` and `py`. Thus, the final dereference outside of the
// loop is guaranteed to be valid. (The final comparison will overlap
// with the last comparison done in the loop for lengths that aren't
// multiples of four.)
//
// Finally, we needn't worry about alignment here, since we do
// unaligned loads.
unsafe {
let (mut px, mut py) = (x.as_ptr(), y.as_ptr());
let (pxend, pyend) = (px.add(x.len() - 4), py.add(y.len() - 4));
while px < pxend {
let vx = (px as *const u32).read_unaligned();
let vy = (py as *const u32).read_unaligned();
if vx != vy {
return false;
}
px = px.add(4);
py = py.add(4);
}
let vx = (pxend as *const u32).read_unaligned();
let vy = (pyend as *const u32).read_unaligned();
vx == vy
}
}
}