mirror of
https://github.com/superseriousbusiness/gotosocial.git
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98263a7de6
* start fixing up tests * fix up tests + automate with drone * fiddle with linting * messing about with drone.yml * some more fiddling * hmmm * add cache * add vendor directory * verbose * ci updates * update some little things * update sig
499 lines
16 KiB
Go
499 lines
16 KiB
Go
// Copyright 2020 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package s2
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import (
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"sort"
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)
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const (
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// A special label indicating that the ContentsIterator done is true.
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cellIndexDoneContents = -1
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)
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// cellIndexNode represents a node in the CellIndex. Cells are organized in a
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// tree such that the ancestors of a given node contain that node.
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type cellIndexNode struct {
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cellID CellID
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label int32
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parent int32
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}
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// newCellIndexNode returns a node with the appropriate default values.
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func newCellIndexNode() cellIndexNode {
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return cellIndexNode{
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cellID: 0,
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label: cellIndexDoneContents,
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parent: -1,
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}
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}
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// A rangeNode represents a range of leaf CellIDs. The range starts at
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// startID (a leaf cell) and ends at the startID field of the next
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// rangeNode. contents points to the node of the CellIndex cellTree
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// representing the cells that overlap this range.
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type rangeNode struct {
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startID CellID // First leaf cell contained by this range.
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contents int32 // Contents of this node (an index within the cell tree).
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}
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// CellIndexIterator is an iterator that visits the entire set of indexed
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// (CellID, label) pairs in an unspecified order.
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type CellIndexIterator struct {
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// TODO(roberts): Implement
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}
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// NewCellIndexIterator creates an iterator for the given CellIndex.
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func NewCellIndexIterator(index *CellIndex) *CellIndexIterator {
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return &CellIndexIterator{}
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}
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// CellIndexRangeIterator is an iterator that seeks and iterates over a set of
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// non-overlapping leaf cell ranges that cover the entire sphere. The indexed
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// (CellID, label) pairs that intersect the current leaf cell range can be
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// visited using CellIndexContentsIterator (see below).
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type CellIndexRangeIterator struct {
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rangeNodes []rangeNode
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pos int
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nonEmpty bool
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}
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// NewCellIndexRangeIterator creates an iterator for the given CellIndex.
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// The iterator is initially *unpositioned*; you must call a positioning method
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// such as Begin() or Seek() before accessing its contents.
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func NewCellIndexRangeIterator(index *CellIndex) *CellIndexRangeIterator {
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return &CellIndexRangeIterator{
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rangeNodes: index.rangeNodes,
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}
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}
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// NewCellIndexNonEmptyRangeIterator creates an iterator for the given CellIndex.
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// The iterator is initially *unpositioned*; you must call a positioning method such as
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// Begin() or Seek() before accessing its contents.
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func NewCellIndexNonEmptyRangeIterator(index *CellIndex) *CellIndexRangeIterator {
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return &CellIndexRangeIterator{
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rangeNodes: index.rangeNodes,
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nonEmpty: true,
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}
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}
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// StartID reports the CellID of the start of the current range of leaf CellIDs.
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//
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// If done is true, this returns the last possible CellID. This property means
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// that most loops do not need to test done explicitly.
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func (c *CellIndexRangeIterator) StartID() CellID {
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return c.rangeNodes[c.pos].startID
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}
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// LimitID reports the non-inclusive end of the current range of leaf CellIDs.
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//
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// This assumes the iterator is not done.
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func (c *CellIndexRangeIterator) LimitID() CellID {
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return c.rangeNodes[c.pos+1].startID
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}
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// IsEmpty reports if no (CellID, label) pairs intersect this range.
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// Also returns true if done() is true.
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func (c *CellIndexRangeIterator) IsEmpty() bool {
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return c.rangeNodes[c.pos].contents == cellIndexDoneContents
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}
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// Begin positions the iterator at the first range of leaf cells (if any).
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func (c *CellIndexRangeIterator) Begin() {
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c.pos = 0
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for c.nonEmpty && c.IsEmpty() && !c.Done() {
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c.pos++
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}
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}
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// Prev positions the iterator at the previous entry and reports whether it was not
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// already positioned at the beginning.
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func (c *CellIndexRangeIterator) Prev() bool {
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if c.nonEmpty {
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return c.nonEmptyPrev()
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}
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return c.prev()
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}
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// prev is used to position the iterator at the previous entry without checking
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// if nonEmpty is true to prevent unwanted recursion.
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func (c *CellIndexRangeIterator) prev() bool {
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if c.pos == 0 {
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return false
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}
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c.pos--
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return true
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}
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// Prev positions the iterator at the previous entry, and reports whether it was
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// already positioned at the beginning.
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func (c *CellIndexRangeIterator) nonEmptyPrev() bool {
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for c.prev() {
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if !c.IsEmpty() {
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return true
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}
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}
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// Return the iterator to its original position.
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if c.IsEmpty() && !c.Done() {
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c.Next()
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}
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return false
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}
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// Next advances the iterator to the next range of leaf cells.
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//
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// This assumes the iterator is not done.
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func (c *CellIndexRangeIterator) Next() {
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c.pos++
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for c.nonEmpty && c.IsEmpty() && !c.Done() {
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c.pos++
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}
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}
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// Advance reports if advancing would leave it positioned on a valid range. If
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// the value would not be valid, the positioning is not changed.
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func (c *CellIndexRangeIterator) Advance(n int) bool {
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// Note that the last element of rangeNodes is a sentinel value.
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if n >= len(c.rangeNodes)-1-c.pos {
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return false
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}
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c.pos += n
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return true
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}
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// Finish positions the iterator so that done is true.
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func (c *CellIndexRangeIterator) Finish() {
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// Note that the last element of rangeNodes is a sentinel value.
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c.pos = len(c.rangeNodes) - 1
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}
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// Done reports if the iterator is positioned beyond the last valid range.
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func (c *CellIndexRangeIterator) Done() bool {
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return c.pos >= len(c.rangeNodes)-1
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}
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// Seek positions the iterator at the first range with startID >= target.
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// Such an entry always exists as long as "target" is a valid leaf cell.
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//
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// Note that it is valid to access startID even when done is true.
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func (c *CellIndexRangeIterator) Seek(target CellID) {
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c.pos = sort.Search(len(c.rangeNodes), func(i int) bool {
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return c.rangeNodes[i].startID > target
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}) - 1
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// Ensure we don't go beyond the beginning.
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if c.pos < 0 {
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c.pos = 0
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}
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// Nonempty needs to find the next non-empty entry.
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for c.nonEmpty && c.IsEmpty() && !c.Done() {
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// c.Next()
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c.pos++
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}
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}
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// CellIndexContentsIterator is an iterator that visits the (CellID, label) pairs
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// that cover a set of leaf cell ranges (see CellIndexRangeIterator). Note that
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// when multiple leaf cell ranges are visited, this iterator only guarantees that
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// each result will be reported at least once, i.e. duplicate values may be
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// suppressed. If you want duplicate values to be reported again, be sure to call
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// Clear first.
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//
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// In particular, the implementation guarantees that when multiple leaf
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// cell ranges are visited in monotonically increasing order, then each
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// (CellID, label) pair is reported exactly once.
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type CellIndexContentsIterator struct {
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// The maximum index within the cellTree slice visited during the
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// previous call to StartUnion. This is used to eliminate duplicate
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// values when StartUnion is called multiple times.
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nodeCutoff int32
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// The maximum index within the cellTree visited during the
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// current call to StartUnion. This is used to update nodeCutoff.
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nextNodeCutoff int32
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// The value of startID from the previous call to StartUnion.
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// This is used to check whether these values are monotonically
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// increasing.
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prevStartID CellID
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// The cell tree from CellIndex
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cellTree []cellIndexNode
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// A copy of the current node in the cell tree.
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node cellIndexNode
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}
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// NewCellIndexContentsIterator returns a new contents iterator.
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//
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// Note that the iterator needs to be positioned using StartUnion before
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// it can be safely used.
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func NewCellIndexContentsIterator(index *CellIndex) *CellIndexContentsIterator {
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it := &CellIndexContentsIterator{
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cellTree: index.cellTree,
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prevStartID: 0,
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nodeCutoff: -1,
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nextNodeCutoff: -1,
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node: cellIndexNode{label: cellIndexDoneContents},
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}
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return it
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}
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// Clear clears all state with respect to which range(s) have been visited.
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func (c *CellIndexContentsIterator) Clear() {
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c.prevStartID = 0
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c.nodeCutoff = -1
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c.nextNodeCutoff = -1
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c.node.label = cellIndexDoneContents
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}
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// CellID returns the current CellID.
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func (c *CellIndexContentsIterator) CellID() CellID {
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return c.node.cellID
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}
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// Label returns the current Label.
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func (c *CellIndexContentsIterator) Label() int32 {
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return c.node.label
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}
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// Next advances the iterator to the next (CellID, label) pair covered by the
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// current leaf cell range.
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//
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// This requires the iterator to not be done.
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func (c *CellIndexContentsIterator) Next() {
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if c.node.parent <= c.nodeCutoff {
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// We have already processed this node and its ancestors.
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c.nodeCutoff = c.nextNodeCutoff
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c.node.label = cellIndexDoneContents
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} else {
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c.node = c.cellTree[c.node.parent]
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}
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}
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// Done reports if all (CellID, label) pairs have been visited.
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func (c *CellIndexContentsIterator) Done() bool {
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return c.node.label == cellIndexDoneContents
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}
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// StartUnion positions the ContentsIterator at the first (cell_id, label) pair
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// that covers the given leaf cell range. Note that when multiple leaf cell
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// ranges are visited using the same ContentsIterator, duplicate values
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// may be suppressed. If you don't want this behavior, call Reset() first.
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func (c *CellIndexContentsIterator) StartUnion(r *CellIndexRangeIterator) {
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if r.StartID() < c.prevStartID {
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c.nodeCutoff = -1 // Can't automatically eliminate duplicates.
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}
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c.prevStartID = r.StartID()
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contents := r.rangeNodes[r.pos].contents
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if contents <= c.nodeCutoff {
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c.node.label = cellIndexDoneContents
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} else {
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c.node = c.cellTree[contents]
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}
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// When visiting ancestors, we can stop as soon as the node index is smaller
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// than any previously visited node index. Because indexes are assigned
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// using a preorder traversal, such nodes are guaranteed to have already
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// been reported.
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c.nextNodeCutoff = contents
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}
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// CellIndex stores a collection of (CellID, label) pairs.
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//
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// The CellIDs may be overlapping or contain duplicate values. For example, a
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// CellIndex could store a collection of CellUnions, where each CellUnion
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// gets its own non-negative int32 label.
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//
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// Similar to ShapeIndex and PointIndex which map each stored element to an
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// identifier, CellIndex stores a label that is typically used to map the
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// results of queries back to client's specific data.
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//
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// The zero value for a CellIndex is sufficient when constructing a CellIndex.
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//
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// To build a CellIndex where each Cell has a distinct label, call Add for each
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// (CellID, label) pair, and then Build the index. For example:
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//
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// // contents is a mapping of an identifier in my system (restaurantID,
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// // vehicleID, etc) to a CellID
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// var contents = map[int32]CellID{...}
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//
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// for key, val := range contents {
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// index.Add(val, key)
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// }
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//
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// index.Build()
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//
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// There is also a helper method that adds all elements of CellUnion with the
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// same label:
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//
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// index.AddCellUnion(cellUnion, label)
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//
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// Note that the index is not dynamic; the contents of the index cannot be
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// changed once it has been built. Adding more after calling Build results in
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// undefined behavior of the index.
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//
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// There are several options for retrieving data from the index. The simplest
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// is to use a built-in method such as IntersectingLabels (which returns
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// the labels of all cells that intersect a given target CellUnion):
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//
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// labels := index.IntersectingLabels(targetUnion);
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//
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// Alternatively, you can use a ClosestCellQuery which computes the cell(s)
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// that are closest to a given target geometry.
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//
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// For example, here is how to find all cells that are closer than
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// distanceLimit to a given target point:
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//
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// query := NewClosestCellQuery(cellIndex, opts)
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// target := NewMinDistanceToPointTarget(targetPoint);
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// for result := range query.FindCells(target) {
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// // result.Distance() is the distance to the target.
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// // result.CellID() is the indexed CellID.
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// // result.Label() is the label associated with the CellID.
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// DoSomething(targetPoint, result);
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// }
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//
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// Internally, the index consists of a set of non-overlapping leaf cell ranges
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// that subdivide the sphere and such that each range intersects a particular
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// set of (cellID, label) pairs.
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//
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// Most clients should use either the methods such as VisitIntersectingCells
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// and IntersectingLabels, or a helper such as ClosestCellQuery.
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type CellIndex struct {
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// A tree of (cellID, label) pairs such that if X is an ancestor of Y, then
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// X.cellID contains Y.cellID. The contents of a given range of leaf
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// cells can be represented by pointing to a node of this tree.
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cellTree []cellIndexNode
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// The last element of rangeNodes is a sentinel value, which is necessary
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// in order to represent the range covered by the previous element.
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rangeNodes []rangeNode
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}
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// Add adds the given CellID and Label to the index.
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func (c *CellIndex) Add(id CellID, label int32) {
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if label < 0 {
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panic("labels must be non-negative")
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}
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c.cellTree = append(c.cellTree, cellIndexNode{cellID: id, label: label, parent: -1})
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}
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// AddCellUnion adds all of the elements of the given CellUnion to the index with the same label.
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func (c *CellIndex) AddCellUnion(cu CellUnion, label int32) {
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if label < 0 {
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panic("labels must be non-negative")
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}
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for _, cell := range cu {
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c.Add(cell, label)
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}
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}
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// Build builds the index for use. This method should only be called once.
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func (c *CellIndex) Build() {
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// To build the cell tree and leaf cell ranges, we maintain a stack of
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// (CellID, label) pairs that contain the current leaf cell. This struct
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// represents an instruction to push or pop a (cellID, label) pair.
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//
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// If label >= 0, the (cellID, label) pair is pushed on the stack.
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// If CellID == SentinelCellID, a pair is popped from the stack.
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// Otherwise the stack is unchanged but a rangeNode is still emitted.
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// delta represents an entry in a stack of (CellID, label) pairs used in the
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// construction of the CellIndex structure.
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type delta struct {
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startID CellID
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cellID CellID
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label int32
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}
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deltas := make([]delta, 0, 2*len(c.cellTree)+2)
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// Create two deltas for each (cellID, label) pair: one to add the pair to
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// the stack (at the start of its leaf cell range), and one to remove it from
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// the stack (at the end of its leaf cell range).
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for _, node := range c.cellTree {
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deltas = append(deltas, delta{
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startID: node.cellID.RangeMin(),
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cellID: node.cellID,
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label: node.label,
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})
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deltas = append(deltas, delta{
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startID: node.cellID.RangeMax().Next(),
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cellID: SentinelCellID,
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label: -1,
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})
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}
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// We also create two special deltas to ensure that a RangeNode is emitted at
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// the beginning and end of the CellID range.
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deltas = append(deltas, delta{
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startID: CellIDFromFace(0).ChildBeginAtLevel(maxLevel),
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cellID: CellID(0),
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label: -1,
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})
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deltas = append(deltas, delta{
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startID: CellIDFromFace(5).ChildEndAtLevel(maxLevel),
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cellID: CellID(0),
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label: -1,
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})
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sort.Slice(deltas, func(i, j int) bool {
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// deltas are sorted first by startID, then in reverse order by cellID,
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// and then by label. This is necessary to ensure that (1) larger cells
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// are pushed on the stack before smaller cells, and (2) cells are popped
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// off the stack before any new cells are added.
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if si, sj := deltas[i].startID, deltas[j].startID; si != sj {
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return si < sj
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}
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if si, sj := deltas[i].cellID, deltas[j].cellID; si != sj {
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return si > sj
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}
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return deltas[i].label < deltas[j].label
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})
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// Now walk through the deltas to build the leaf cell ranges and cell tree
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// (which is essentially a permanent form of the "stack" described above).
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c.cellTree = nil
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c.rangeNodes = nil
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contents := int32(-1)
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for i := 0; i < len(deltas); {
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startID := deltas[i].startID
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// Process all the deltas associated with the current startID.
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for ; i < len(deltas) && deltas[i].startID == startID; i++ {
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if deltas[i].label >= 0 {
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c.cellTree = append(c.cellTree, cellIndexNode{
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cellID: deltas[i].cellID,
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label: deltas[i].label,
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parent: contents})
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contents = int32(len(c.cellTree) - 1)
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} else if deltas[i].cellID == SentinelCellID {
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contents = c.cellTree[contents].parent
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}
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}
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c.rangeNodes = append(c.rangeNodes, rangeNode{startID, contents})
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}
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}
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// TODO(roberts): Differences from C++
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// IntersectingLabels
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// VisitIntersectingCells
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// CellIndexIterator
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