Struct memchr::arch::all::rabinkarp::Finder

pub struct Finder {
    hash: Hash,
    hash_2pow: u32,
}

A forward substring searcher using the Rabin-Karp algorithm.

Note that, as a lower level API, a Finder does not have access to the needle it was constructed with. For this reason, executing a search with a Finder requires passing both the needle and the haystack, where the needle is exactly equivalent to the one given to the Finder at construction time. This design was chosen so that callers can have more precise control over where and how many times a needle is stored. For example, in cases where Rabin-Karp is just one of several possible substring search algorithms.

Fields

hash: Hash

The actual hash.

hash_2pow: u32

The factor needed to multiply a byte by in order to subtract it from the hash. It is defined to be 2^(n-1) (using wrapping exponentiation), where n is the length of the needle. This is how we “remove” a byte from the hash once the hash window rolls past it.

Implementations

impl Finder

pub fn new(needle: &[u8]) -> Finder

Create a new Rabin-Karp forward searcher for the given needle.

The needle may be empty. The empty needle matches at every byte offset.

Note that callers must pass the same needle to all search calls using this Finder.

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

Return the first occurrence of the needle in the haystack given. If no such occurrence exists, then None is returned.

The needle provided must match the needle given to this finder at construction time.

The maximum value this can return is haystack.len(), which can only occur when the needle and haystack both have length zero. Otherwise, for non-empty haystacks, the maximum value is haystack.len() - 1.

pub unsafe fn find_raw( &self, hstart: *const u8, hend: *const u8, nstart: *const u8, nend: *const u8, ) -> Option<*const u8>

Like find, but accepts and returns raw pointers.

When a match is found, the pointer returned is guaranteed to be >= start and <= end. The pointer returned is only ever equivalent to end when both the needle and haystack are empty. (That is, the empty string matches the empty string.)

This routine is useful if you’re already using raw pointers and would like to avoid converting back to a slice before executing a search.

Safety

Note that start and end below refer to both pairs of pointers given to this routine. That is, the conditions apply to both hstart/hend and nstart/nend.

• Both start and end must be valid for reads.
• Both start and end must point to an initialized value.
• Both start and end must point to the same allocated object and must either be in bounds or at most one byte past the end of the allocated object.
• Both start and end must be derived from a pointer to the same object.
• The distance between start and end must not overflow isize.
• The distance being in bounds must not rely on “wrapping around” the address space.
• It must be the case that start <= end.

Trait Implementations

impl Clone for Finder

fn clone(&self) -> Finder

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Finder

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

Formats the value using the given formatter.