Struct Signature 

pub struct Signature(/* private fields */);

A tag built by setting one bit per attribute value, so that a conjunction of required values is a subset test.

Superimposed coding, which is old and still the right answer when the test has to be one instruction on a value that is already in a register. Each attribute and value pair hashes to one of 64 bits. A member’s tag is the bits for the values it has. A query’s tag is the bits for the values it requires. The member is worth ranking when it has all of the query’s bits.

Two different values can land on the same bit, so a member can pass a filter it does not really match. It can never fail one it does match, which is the direction that matters: the answers are a superset of the truth and the caller’s own predicate cuts them down, where the other way round would lose answers silently.

use yo_vector::Signature;

// What a document is tagged with, and what a query asks for.
let doc = Signature::of(&[("lang", "en".as_bytes()), ("topic", "finance".as_bytes())]);
let english = Signature::of(&[("lang", "en".as_bytes())]);

assert!(doc.covers(english));
// The other way round only holds if the two bits happened to collide.
assert!(!english.covers(doc) || english.bits() == doc.bits());

Implementations

impl Signature

pub fn of(values: &[(&str, &[u8])]) -> Signature

The signature of a set of attribute and value pairs.

pub fn bits(self) -> u64

The signature as the tag to hand to Partitions::insert_tagged.

pub fn from_bits(bits: u64) -> Signature

The signature of a tag that came back out of the index.

pub fn covers(self, want: Signature) -> bool

Whether this has every bit want has, which is the test the scan runs.

Trait Implementations

impl Clone for Signature

fn clone(&self) -> Signature

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Signature

impl Debug for Signature

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

Formats the value using the given formatter.

impl Default for Signature

fn default() -> Signature

Returns the “default value” for a type.

impl Eq for Signature

impl Filter for Signature

fn allows(&self, tag: u64) -> bool

Whether a member with this tag is worth ranking.

impl PartialEq for Signature

fn eq(&self, other: &Signature) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Signature