Module memchr::arch::all::twoway

An implementation of the Two-Way substring search algorithm.

Finder can be built for forward searches, while FinderRev can be built for reverse searches.

Two-Way makes for a nice general purpose substring search algorithm because of its time and space complexity properties. It also performs well in practice. Namely, with m = len(needle) and n = len(haystack), Two-Way takes O(m) time to create a finder, O(1) space and O(n) search time. In other words, the preprocessing step is quick, doesn’t require any heap memory and the worst case search time is guaranteed to be linear in the haystack regardless of the size of the needle.

While vector algorithms will usually beat Two-Way handedly, vector algorithms also usually have pathological or edge cases that are better handled by Two-Way. Moreover, not all targets support vector algorithms or implementations for them simply may not exist yet.

Two-Way can be found in the memmem implementations in at least GNU libc and musl.

Structs

• ApproximateByteSet 🔒
  A bitset used to track whether a particular byte exists in a needle or not.
• Finder
  A forward substring searcher that uses the Two-Way algorithm.
• FinderRev
  A reverse substring searcher that uses the Two-Way algorithm.
• Suffix 🔒
  A suffix extracted from a needle along with its period.
• TwoWay 🔒
  An implementation of the TwoWay substring search algorithm.

Enums

• Shift 🔒
  A representation of the amount we’re allowed to shift by during Two-Way search.
• SuffixKind 🔒
  The kind of suffix to extract.
• SuffixOrdering 🔒
  The result of comparing corresponding bytes between two suffixes.