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use std::borrow::{Borrow, BorrowMut};
use crate::fastfield::AliveBitSet;
use crate::DocId;
/// Sentinel value returned when a [`DocSet`] has been entirely consumed.
///
/// This is not `u32::MAX` as one would have expected, due to the lack of SSE2 instructions
/// to compare `[u32; 4]`.
pub const TERMINATED: DocId = i32::MAX as u32;
/// The collect_block method on `SegmentCollector` uses a buffer of this size.
/// Passed results to `collect_block` will not exceed this size and will be
/// exactly this size as long as we can fill the buffer.
pub const COLLECT_BLOCK_BUFFER_LEN: usize = 64;
/// Represents an iterable set of sorted doc ids.
pub trait DocSet: Send {
/// Goes to the next element.
///
/// The DocId of the next element is returned.
/// In other words we should always have :
/// ```compile_fail
/// let doc = docset.advance();
/// assert_eq!(doc, docset.doc());
/// ```
///
/// If we reached the end of the `DocSet`, [`TERMINATED`] should be returned.
///
/// Calling `.advance()` on a terminated `DocSet` should be supported, and [`TERMINATED`] should
/// be returned.
fn advance(&mut self) -> DocId;
/// Advances the `DocSet` forward until reaching the target, or going to the
/// lowest [`DocId`] greater than the target.
///
/// If the end of the `DocSet` is reached, [`TERMINATED`] is returned.
///
/// Calling `.seek(target)` on a terminated `DocSet` is legal. Implementation
/// of `DocSet` should support it.
///
/// Calling `seek(TERMINATED)` is also legal and is the normal way to consume a `DocSet`.
///
/// `target` has to be larger or equal to `.doc()` when calling `seek`.
fn seek(&mut self, target: DocId) -> DocId {
let mut doc = self.doc();
debug_assert!(doc <= target);
while doc < target {
doc = self.advance();
}
doc
}
/// Seeks to the target if possible and returns true if the target is in the DocSet.
///
/// DocSets that already have an efficient `seek` method don't need to implement
/// `seek_into_the_danger_zone`. All wrapper DocSets should forward
/// `seek_into_the_danger_zone` to the underlying DocSet.
///
/// ## API Behaviour
/// If `seek_into_the_danger_zone` is returning true, a call to `doc()` has to return target.
/// If `seek_into_the_danger_zone` is returning false, a call to `doc()` may return any doc
/// between the last doc that matched and target or a doc that is a valid next hit after
/// target. The DocSet is considered to be in an invalid state until
/// `seek_into_the_danger_zone` returns true again.
///
/// `target` needs to be equal or larger than `doc` when in a valid state.
///
/// Consecutive calls are not allowed to have decreasing `target` values.
///
/// # Warning
/// This is an advanced API used by intersection. The API contract is tricky, avoid using it.
fn seek_into_the_danger_zone(&mut self, target: DocId) -> bool {
let current_doc = self.doc();
if current_doc < target {
self.seek(target);
}
self.doc() == target
}
/// Fills a given mutable buffer with the next doc ids from the
/// `DocSet`
///
/// If that many `DocId`s are available, the method should
/// fill the entire buffer and return the length of the buffer.
///
/// If we reach the end of the `DocSet` before filling
/// it entirely, then the buffer is filled up to this point, and
/// return value is the number of elements that were filled.
///
/// # Warning
///
/// This method is only here for specific high-performance
/// use case where batching. The normal way to
/// go through the `DocId`'s is to call `.advance()`.
fn fill_buffer(&mut self, buffer: &mut [DocId; COLLECT_BLOCK_BUFFER_LEN]) -> usize {
if self.doc() == TERMINATED {
return 0;
}
for (i, buffer_val) in buffer.iter_mut().enumerate() {
*buffer_val = self.doc();
if self.advance() == TERMINATED {
return i + 1;
}
}
buffer.len()
}
/// Returns the current document
/// Right after creating a new `DocSet`, the docset points to the first document.
///
/// If the `DocSet` is empty, `.doc()` should return [`TERMINATED`].
fn doc(&self) -> DocId;
/// Returns a best-effort hint of the
/// length of the docset.
fn size_hint(&self) -> u32;
/// Returns a best-effort hint of the cost to consume the entire docset.
///
/// Consuming means calling advance until [`TERMINATED`] is returned.
/// The cost should be relative to the cost of driving a Term query,
/// which would be the number of documents in the DocSet.
///
/// By default this returns `size_hint()`.
///
/// DocSets may have vastly different cost depending on their type,
/// e.g. an intersection with 10 hits is much cheaper than
/// a phrase search with 10 hits, since it needs to load positions.
///
/// ### Future Work
/// We may want to differentiate `DocSet` costs more more granular, e.g.
/// creation_cost, advance_cost, seek_cost on to get a good estimation
/// what query types to choose.
fn cost(&self) -> u64 {
self.size_hint() as u64
}
/// Returns the number documents matching.
/// Calling this method consumes the `DocSet`.
fn count(&mut self, alive_bitset: &AliveBitSet) -> u32 {
let mut count = 0u32;
let mut doc = self.doc();
while doc != TERMINATED {
if alive_bitset.is_alive(doc) {
count += 1u32;
}
doc = self.advance();
}
count
}
/// Returns the count of documents, deleted or not.
/// Calling this method consumes the `DocSet`.
///
/// Of course, the result is an upper bound of the result
/// given by `count()`.
fn count_including_deleted(&mut self) -> u32 {
let mut count = 0u32;
let mut doc = self.doc();
while doc != TERMINATED {
count += 1u32;
doc = self.advance();
}
count
}
}
impl DocSet for &mut dyn DocSet {
fn advance(&mut self) -> u32 {
(**self).advance()
}
fn seek(&mut self, target: DocId) -> DocId {
(**self).seek(target)
}
fn seek_into_the_danger_zone(&mut self, target: DocId) -> bool {
(**self).seek_into_the_danger_zone(target)
}
fn doc(&self) -> u32 {
(**self).doc()
}
fn size_hint(&self) -> u32 {
(**self).size_hint()
}
fn cost(&self) -> u64 {
(**self).cost()
}
fn count(&mut self, alive_bitset: &AliveBitSet) -> u32 {
(**self).count(alive_bitset)
}
fn count_including_deleted(&mut self) -> u32 {
(**self).count_including_deleted()
}
}
impl<TDocSet: DocSet + ?Sized> DocSet for Box<TDocSet> {
fn advance(&mut self) -> DocId {
let unboxed: &mut TDocSet = self.borrow_mut();
unboxed.advance()
}
fn seek(&mut self, target: DocId) -> DocId {
let unboxed: &mut TDocSet = self.borrow_mut();
unboxed.seek(target)
}
fn seek_into_the_danger_zone(&mut self, target: DocId) -> bool {
let unboxed: &mut TDocSet = self.borrow_mut();
unboxed.seek_into_the_danger_zone(target)
}
fn fill_buffer(&mut self, buffer: &mut [DocId; COLLECT_BLOCK_BUFFER_LEN]) -> usize {
let unboxed: &mut TDocSet = self.borrow_mut();
unboxed.fill_buffer(buffer)
}
fn doc(&self) -> DocId {
let unboxed: &TDocSet = self.borrow();
unboxed.doc()
}
fn size_hint(&self) -> u32 {
let unboxed: &TDocSet = self.borrow();
unboxed.size_hint()
}
fn cost(&self) -> u64 {
let unboxed: &TDocSet = self.borrow();
unboxed.cost()
}
fn count(&mut self, alive_bitset: &AliveBitSet) -> u32 {
let unboxed: &mut TDocSet = self.borrow_mut();
unboxed.count(alive_bitset)
}
fn count_including_deleted(&mut self) -> u32 {
let unboxed: &mut TDocSet = self.borrow_mut();
unboxed.count_including_deleted()
}
}