1 files changed, 175 insertions, 0 deletions
diff --git a/vendor/github.com/golang/geo/s2/lexicon.go b/vendor/github.com/golang/geo/s2/lexicon.go
new file mode 100644
index 000000000..41cbffdc2
--- /dev/null
+++ b/vendor/github.com/golang/geo/s2/lexicon.go
@@ -0,0 +1,175 @@
+// Copyright 2020 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package s2
+
+import (
+	"encoding/binary"
+	"hash/adler32"
+	"math"
+	"sort"
+)
+
+// TODO(roberts): If any of these are worth making public, change the
+// method signatures and type names.
+
+// emptySetID represents the last ID that will ever be generated.
+// (Non-negative IDs are reserved for singleton sets.)
+var emptySetID = int32(math.MinInt32)
+
+// idSetLexicon compactly represents a set of non-negative
+// integers such as array indices ("ID sets"). It is especially suitable when
+// either (1) there are many duplicate sets, or (2) there are many singleton
+// or empty sets. See also sequenceLexicon.
+//
+// Each distinct ID set is mapped to a 32-bit integer. Empty and singleton
+// sets take up no additional space; the set itself is represented
+// by the unique ID assigned to the set. Duplicate sets are automatically
+// eliminated. Note also that ID sets are referred to using 32-bit integers
+// rather than pointers.
+type idSetLexicon struct {
+	idSets *sequenceLexicon
+}
+
+func newIDSetLexicon() *idSetLexicon {
+	return &idSetLexicon{
+		idSets: newSequenceLexicon(),
+	}
+}
+
+// add adds the given set of integers to the lexicon if it is not already
+// present, and return the unique ID for this set. The values are automatically
+// sorted and duplicates are removed.
+//
+// The primary difference between this and sequenceLexicon are:
+// 1. Empty and singleton sets are represented implicitly; they use no space.
+// 2. Sets are represented rather than sequences; the ordering of values is
+//    not important and duplicates are removed.
+// 3. The values must be 32-bit non-negative integers only.
+func (l *idSetLexicon) add(ids ...int32) int32 {
+	// Empty sets have a special ID chosen not to conflict with other IDs.
+	if len(ids) == 0 {
+		return emptySetID
+	}
+
+	// Singleton sets are represented by their element.
+	if len(ids) == 1 {
+		return ids[0]
+	}
+
+	// Canonicalize the set by sorting and removing duplicates.
+	//
+	// Creates a new slice in order to not alter the supplied values.
+	set := uniqueInt32s(ids)
+
+	// Non-singleton sets are represented by the bitwise complement of the ID
+	// returned by the sequenceLexicon
+	return ^l.idSets.add(set)
+}
+
+// idSet returns the set of integers corresponding to an ID returned by add.
+func (l *idSetLexicon) idSet(setID int32) []int32 {
+	if setID >= 0 {
+		return []int32{setID}
+	}
+	if setID == emptySetID {
+		return []int32{}
+	}
+
+	return l.idSets.sequence(^setID)
+}
+
+func (l *idSetLexicon) clear() {
+	l.idSets.clear()
+}
+
+// sequenceLexicon compactly represents a sequence of values (e.g., tuples).
+// It automatically eliminates duplicates slices, and maps the remaining
+// sequences to sequentially increasing integer IDs. See also idSetLexicon.
+//
+// Each distinct sequence is mapped to a 32-bit integer.
+type sequenceLexicon struct {
+	values []int32
+	begins []uint32
+
+	// idSet is a mapping of a sequence hash to sequence index in the lexicon.
+	idSet map[uint32]int32
+}
+
+func newSequenceLexicon() *sequenceLexicon {
+	return &sequenceLexicon{
+		begins: []uint32{0},
+		idSet:  make(map[uint32]int32),
+	}
+}
+
+// clears all data from the lexicon.
+func (l *sequenceLexicon) clear() {
+	l.values = nil
+	l.begins = []uint32{0}
+	l.idSet = make(map[uint32]int32)
+}
+
+// add adds the given value to the lexicon if it is not already present, and
+// returns its ID. IDs are assigned sequentially starting from zero.
+func (l *sequenceLexicon) add(ids []int32) int32 {
+	if id, ok := l.idSet[hashSet(ids)]; ok {
+		return id
+	}
+	for _, v := range ids {
+		l.values = append(l.values, v)
+	}
+	l.begins = append(l.begins, uint32(len(l.values)))
+
+	id := int32(len(l.begins)) - 2
+	l.idSet[hashSet(ids)] = id
+
+	return id
+}
+
+// sequence returns the original sequence of values for the given ID.
+func (l *sequenceLexicon) sequence(id int32) []int32 {
+	return l.values[l.begins[id]:l.begins[id+1]]
+}
+
+// size reports the number of value sequences in the lexicon.
+func (l *sequenceLexicon) size() int {
+	// Subtract one because the list of begins starts out with the first element set to 0.
+	return len(l.begins) - 1
+}
+
+// hash returns a hash of this sequence of int32s.
+func hashSet(s []int32) uint32 {
+	// TODO(roberts): We just need a way to nicely hash all the values down to
+	// a 32-bit value. To ensure no unnecessary dependencies we use the core
+	// library types available to do this. Is there a better option?
+	a := adler32.New()
+	binary.Write(a, binary.LittleEndian, s)
+	return a.Sum32()
+}
+
+// uniqueInt32s returns the sorted and uniqued set of int32s from the input.
+func uniqueInt32s(in []int32) []int32 {
+	var vals []int32
+	m := make(map[int32]bool)
+	for _, i := range in {
+		if m[i] {
+			continue
+		}
+		m[i] = true
+		vals = append(vals, i)
+	}
+	sort.Slice(vals, func(i, j int) bool { return vals[i] < vals[j] })
+	return vals
+}