/*!
A 256-bit vector implementation of the "packed pair" SIMD algorithm.
The "packed pair" algorithm is based on the [generic SIMD] algorithm. The main
difference is that it (by default) uses a background distribution of byte
frequencies to heuristically select the pair of bytes to search for.
[generic SIMD]: http://0x80.pl/articles/simd-strfind.html#first-and-last
*/
use core::arch::x86_64::{__m128i, __m256i};
use crate::arch::{all::packedpair::Pair, generic::packedpair};
/// A "packed pair" finder that uses 256-bit vector operations.
///
/// This finder picks two bytes that it believes have high predictive power
/// for indicating an overall match of a needle. Depending on whether
/// `Finder::find` or `Finder::find_prefilter` is used, it reports offsets
/// where the needle matches or could match. In the prefilter case, candidates
/// are reported whenever the [`Pair`] of bytes given matches.
#[derive(Clone, Copy, Debug)]
pub struct Finder {
sse2: packedpair::Finder<__m128i>,
avx2: packedpair::Finder<__m256i>,
}
impl Finder {
/// Create a new pair searcher. The searcher returned can either report
/// exact matches of `needle` or act as a prefilter and report candidate
/// positions of `needle`.
///
/// If AVX2 is unavailable in the current environment or if a [`Pair`]
/// could not be constructed from the needle given, then `None` is
/// returned.
#[inline]
pub fn new(needle: &[u8]) -> Option<Finder> {
Finder::with_pair(needle, Pair::new(needle)?)
}
/// Create a new "packed pair" finder using the pair of bytes given.
///
/// This constructor permits callers to control precisely which pair of
/// bytes is used as a predicate.
///
/// If AVX2 is unavailable in the current environment, then `None` is
/// returned.
#[inline]
pub fn with_pair(needle: &[u8], pair: Pair) -> Option<Finder> {
if Finder::is_available() {
// SAFETY: we check that sse2/avx2 is available above. We are also
// guaranteed to have needle.len() > 1 because we have a valid
// Pair.
unsafe { Some(Finder::with_pair_impl(needle, pair)) }
} else {
None
}
}
/// Create a new `Finder` specific to SSE2 vectors and routines.
///
/// # Safety
///
/// Same as the safety for `packedpair::Finder::new`, and callers must also
/// ensure that both SSE2 and AVX2 are available.
#[target_feature(enable = "sse2", enable = "avx2")]
#[inline]
unsafe fn with_pair_impl(needle: &[u8], pair: Pair) -> Finder {
let sse2 = packedpair::Finder::<__m128i>::new(needle, pair);
let avx2 = packedpair::Finder::<__m256i>::new(needle, pair);
Finder { sse2, avx2 }
}
/// Returns true when this implementation is available in the current
/// environment.
///
/// When this is true, it is guaranteed that [`Finder::with_pair`] will
/// return a `Some` value. Similarly, when it is false, it is guaranteed
/// that `Finder::with_pair` will return a `None` value. Notice that this
/// does not guarantee that [`Finder::new`] will return a `Finder`. Namely,
/// even when `Finder::is_available` is true, it is not guaranteed that a
/// valid [`Pair`] can be found from the needle given.
///
/// Note also that for the lifetime of a single program, if this returns
/// true then it will always return true.
#[inline]
pub fn is_available() -> bool {
#[cfg(not(target_feature = "sse2"))]
{
false
}
#[cfg(target_feature = "sse2")]
{
#[cfg(target_feature = "avx2")]
{
true
}
#[cfg(not(target_feature = "avx2"))]
{
#[cfg(feature = "std")]
{
std::is_x86_feature_detected!("avx2")
}
#[cfg(not(feature = "std"))]
{
false
}
}
}
}
/// Execute a search using AVX2 vectors and routines.
///
/// # Panics
///
/// When `haystack.len()` is less than [`Finder::min_haystack_len`].
#[inline]
pub fn find(&self, haystack: &[u8], needle: &[u8]) -> Option<usize> {
// SAFETY: Building a `Finder` means it's safe to call 'sse2' routines.
unsafe { self.find_impl(haystack, needle) }
}
/// Run this finder on the given haystack as a prefilter.
///
/// If a candidate match is found, then an offset where the needle *could*
/// begin in the haystack is returned.
///
/// # Panics
///
/// When `haystack.len()` is less than [`Finder::min_haystack_len`].
#[inline]
pub fn find_prefilter(&self, haystack: &[u8]) -> Option<usize> {
// SAFETY: Building a `Finder` means it's safe to call 'sse2' routines.
unsafe { self.find_prefilter_impl(haystack) }
}
/// Execute a search using AVX2 vectors and routines.
///
/// # Panics
///
/// When `haystack.len()` is less than [`Finder::min_haystack_len`].
///
/// # Safety
///
/// (The target feature safety obligation is automatically fulfilled by
/// virtue of being a method on `Finder`, which can only be constructed
/// when it is safe to call `sse2` and `avx2` routines.)
#[target_feature(enable = "sse2", enable = "avx2")]
#[inline]
unsafe fn find_impl(
&self,
haystack: &[u8],
needle: &[u8],
) -> Option<usize> {
if haystack.len() < self.avx2.min_haystack_len() {
self.sse2.find(haystack, needle)
} else {
self.avx2.find(haystack, needle)
}
}
/// Execute a prefilter search using AVX2 vectors and routines.
///
/// # Panics
///
/// When `haystack.len()` is less than [`Finder::min_haystack_len`].
///
/// # Safety
///
/// (The target feature safety obligation is automatically fulfilled by
/// virtue of being a method on `Finder`, which can only be constructed
/// when it is safe to call `sse2` and `avx2` routines.)
#[target_feature(enable = "sse2", enable = "avx2")]
#[inline]
unsafe fn find_prefilter_impl(&self, haystack: &[u8]) -> Option<usize> {
if haystack.len() < self.avx2.min_haystack_len() {
self.sse2.find_prefilter(haystack)
} else {
self.avx2.find_prefilter(haystack)
}
}
/// Returns the pair of offsets (into the needle) used to check as a
/// predicate before confirming whether a needle exists at a particular
/// position.
#[inline]
pub fn pair(&self) -> &Pair {
self.avx2.pair()
}
/// Returns the minimum haystack length that this `Finder` can search.
///
/// Using a haystack with length smaller than this in a search will result
/// in a panic. The reason for this restriction is that this finder is
/// meant to be a low-level component that is part of a larger substring
/// strategy. In that sense, it avoids trying to handle all cases and
/// instead only handles the cases that it can handle very well.
#[inline]
pub fn min_haystack_len(&self) -> usize {
// The caller doesn't need to care about AVX2's min_haystack_len
// since this implementation will automatically switch to the SSE2
// implementation if the haystack is too short for AVX2. Therefore, the
// caller only needs to care about SSE2's min_haystack_len.
//
// This does assume that SSE2's min_haystack_len is less than or
// equal to AVX2's min_haystack_len. In practice, this is true and
// there is no way it could be false based on how this Finder is
// implemented. Namely, both SSE2 and AVX2 use the same `Pair`. If
// they used different pairs, then it's possible (although perhaps
// pathological) for SSE2's min_haystack_len to be bigger than AVX2's.
self.sse2.min_haystack_len()
}
}
#[cfg(test)]
mod tests {
use super::*;
fn find(haystack: &[u8], needle: &[u8]) -> Option<Option<usize>> {
let f = Finder::new(needle)?;
if haystack.len() < f.min_haystack_len() {
return None;
}
Some(f.find(haystack, needle))
}
define_substring_forward_quickcheck!(find);
#[test]
fn forward_substring() {
crate::tests::substring::Runner::new().fwd(find).run()
}
#[test]
fn forward_packedpair() {
fn find(
haystack: &[u8],
needle: &[u8],
index1: u8,
index2: u8,
) -> Option<Option<usize>> {
let pair = Pair::with_indices(needle, index1, index2)?;
let f = Finder::with_pair(needle, pair)?;
if haystack.len() < f.min_haystack_len() {
return None;
}
Some(f.find(haystack, needle))
}
crate::tests::packedpair::Runner::new().fwd(find).run()
}
#[test]
fn forward_packedpair_prefilter() {
fn find(
haystack: &[u8],
needle: &[u8],
index1: u8,
index2: u8,
) -> Option<Option<usize>> {
if !cfg!(target_feature = "sse2") {
return None;
}
let pair = Pair::with_indices(needle, index1, index2)?;
let f = Finder::with_pair(needle, pair)?;
if haystack.len() < f.min_haystack_len() {
return None;
}
Some(f.find_prefilter(haystack))
}
crate::tests::packedpair::Runner::new().fwd(find).run()
}
}
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