Struct memchr::memmem::searcher::Searcher

pub(crate) struct Searcher {
    call: unsafe fn(searcher: &Searcher, prestate: &mut PrefilterState, haystack: &[u8], needle: &[u8]) -> Option<usize>,
    kind: SearcherKind,
    rabinkarp: Finder,
}

A “meta” substring searcher.

To a first approximation, this chooses what it believes to be the “best” substring search implemnetation based on the needle at construction time. Then, every call to find will execute that particular implementation. To a second approximation, multiple substring search algorithms may be used, depending on the haystack. For example, for supremely short haystacks, Rabin-Karp is typically used.

See the documentation on Prefilter for an explanation of the dispatching mechanism. The quick summary is that an enum has too much overhead and we can’t use dynamic dispatch via traits because we need to work in a core-only environment. (Dynamic dispatch works in core-only, but you need &dyn Trait and we really need a Box<dyn Trait> here. The latter requires alloc.) So instead, we use a union and an appropriately paired free function to read from the correct field on the union and execute the chosen substring search implementation.

Fields

call: unsafe fn(searcher: &Searcher, prestate: &mut PrefilterState, haystack: &[u8], needle: &[u8]) -> Option<usize>

kind: SearcherKind

rabinkarp: Finder

Implementations

impl Searcher

pub(crate) fn new<R: HeuristicFrequencyRank>( prefilter: PrefilterConfig, ranker: R, needle: &[u8], ) -> Searcher

Creates a new “meta” substring searcher that attempts to choose the best algorithm based on the needle, heuristics and what the current target supports.

fn twoway( needle: &[u8], rabinkarp: Finder, prestrat: Option<Prefilter>, ) -> Searcher

Creates a new searcher that always uses the Two-Way algorithm. This is typically used when vector algorithms are unavailable or inappropriate. (For example, when the needle is “too long.”)

If a prefilter is given, then the searcher returned will be accelerated by the prefilter.

pub(crate) fn find( &self, prestate: &mut PrefilterState, haystack: &[u8], needle: &[u8], ) -> Option<usize>

Searches the given haystack for the given needle. The needle given should be the same as the needle that this finder was initialized with.

Inlining this can lead to big wins for latency, and #[inline] doesn’t seem to be enough in some cases.

Trait Implementations

impl Clone for Searcher

fn clone(&self) -> Searcher

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Searcher

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.