bench-forgejo/vendor/github.com/couchbase/vellum/fst_iterator.go
2019-11-27 11:23:33 +02:00

303 lines
8.5 KiB
Go
Vendored

// Copyright (c) 2017 Couchbase, Inc.
//
// 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 vellum
import (
"bytes"
)
// Iterator represents a means of visiting key/value pairs in order.
type Iterator interface {
// Current() returns the key/value pair currently pointed to.
// The []byte of the key is ONLY guaranteed to be valid until
// another call to Next/Seek/Close. If you need it beyond that
// point you MUST make a copy.
Current() ([]byte, uint64)
// Next() advances the iterator to the next key/value pair.
// If no more key/value pairs exist, ErrIteratorDone is returned.
Next() error
// Seek() advances the iterator the specified key, or the next key
// if it does not exist.
// If no keys exist after that point, ErrIteratorDone is returned.
Seek(key []byte) error
// Reset resets the Iterator' internal state to allow for iterator
// reuse (e.g. pooling).
Reset(f *FST, startKeyInclusive, endKeyExclusive []byte, aut Automaton) error
// Close() frees any resources held by this iterator.
Close() error
}
// FSTIterator is a structure for iterating key/value pairs in this FST in
// lexicographic order. Iterators should be constructed with the FSTIterator
// method on the parent FST structure.
type FSTIterator struct {
f *FST
aut Automaton
startKeyInclusive []byte
endKeyExclusive []byte
statesStack []fstState
keysStack []byte
keysPosStack []int
valsStack []uint64
autStatesStack []int
nextStart []byte
}
func newIterator(f *FST, startKeyInclusive, endKeyExclusive []byte,
aut Automaton) (*FSTIterator, error) {
rv := &FSTIterator{}
err := rv.Reset(f, startKeyInclusive, endKeyExclusive, aut)
if err != nil {
return nil, err
}
return rv, nil
}
// Reset resets the Iterator' internal state to allow for iterator
// reuse (e.g. pooling).
func (i *FSTIterator) Reset(f *FST,
startKeyInclusive, endKeyExclusive []byte, aut Automaton) error {
if aut == nil {
aut = alwaysMatchAutomaton
}
i.f = f
i.startKeyInclusive = startKeyInclusive
i.endKeyExclusive = endKeyExclusive
i.aut = aut
return i.pointTo(startKeyInclusive)
}
// pointTo attempts to point us to the specified location
func (i *FSTIterator) pointTo(key []byte) error {
// tried to seek before start
if bytes.Compare(key, i.startKeyInclusive) < 0 {
key = i.startKeyInclusive
}
// tried to see past end
if i.endKeyExclusive != nil &&
bytes.Compare(key, i.endKeyExclusive) > 0 {
key = i.endKeyExclusive
}
// reset any state, pointTo always starts over
i.statesStack = i.statesStack[:0]
i.keysStack = i.keysStack[:0]
i.keysPosStack = i.keysPosStack[:0]
i.valsStack = i.valsStack[:0]
i.autStatesStack = i.autStatesStack[:0]
root, err := i.f.decoder.stateAt(i.f.decoder.getRoot(), nil)
if err != nil {
return err
}
autStart := i.aut.Start()
maxQ := -1
// root is always part of the path
i.statesStack = append(i.statesStack, root)
i.autStatesStack = append(i.autStatesStack, autStart)
for j := 0; j < len(key); j++ {
keyJ := key[j]
curr := i.statesStack[len(i.statesStack)-1]
autCurr := i.autStatesStack[len(i.autStatesStack)-1]
pos, nextAddr, nextVal := curr.TransitionFor(keyJ)
if nextAddr == noneAddr {
// needed transition doesn't exist
// find last trans before the one we needed
for q := curr.NumTransitions() - 1; q >= 0; q-- {
if curr.TransitionAt(q) < keyJ {
maxQ = q
break
}
}
break
}
autNext := i.aut.Accept(autCurr, keyJ)
next, err := i.f.decoder.stateAt(nextAddr, nil)
if err != nil {
return err
}
i.statesStack = append(i.statesStack, next)
i.keysStack = append(i.keysStack, keyJ)
i.keysPosStack = append(i.keysPosStack, pos)
i.valsStack = append(i.valsStack, nextVal)
i.autStatesStack = append(i.autStatesStack, autNext)
continue
}
if !i.statesStack[len(i.statesStack)-1].Final() ||
!i.aut.IsMatch(i.autStatesStack[len(i.autStatesStack)-1]) ||
bytes.Compare(i.keysStack, key) < 0 {
return i.next(maxQ)
}
return nil
}
// Current returns the key and value currently pointed to by the iterator.
// If the iterator is not pointing at a valid value (because Iterator/Next/Seek)
// returned an error previously, it may return nil,0.
func (i *FSTIterator) Current() ([]byte, uint64) {
curr := i.statesStack[len(i.statesStack)-1]
if curr.Final() {
var total uint64
for _, v := range i.valsStack {
total += v
}
total += curr.FinalOutput()
return i.keysStack, total
}
return nil, 0
}
// Next advances this iterator to the next key/value pair. If there is none
// or the advancement goes beyond the configured endKeyExclusive, then
// ErrIteratorDone is returned.
func (i *FSTIterator) Next() error {
return i.next(-1)
}
func (i *FSTIterator) next(lastOffset int) error {
// remember where we started with keysStack in this next() call
i.nextStart = append(i.nextStart[:0], i.keysStack...)
nextOffset := lastOffset + 1
allowCompare := false
OUTER:
for true {
curr := i.statesStack[len(i.statesStack)-1]
autCurr := i.autStatesStack[len(i.autStatesStack)-1]
if curr.Final() && i.aut.IsMatch(autCurr) && allowCompare {
// check to see if new keystack might have gone too far
if i.endKeyExclusive != nil &&
bytes.Compare(i.keysStack, i.endKeyExclusive) >= 0 {
return ErrIteratorDone
}
cmp := bytes.Compare(i.keysStack, i.nextStart)
if cmp > 0 {
// in final state greater than start key
return nil
}
}
numTrans := curr.NumTransitions()
INNER:
for nextOffset < numTrans {
t := curr.TransitionAt(nextOffset)
autNext := i.aut.Accept(autCurr, t)
if !i.aut.CanMatch(autNext) {
// TODO: potential optimization to skip nextOffset
// forwards more directly to something that the
// automaton likes rather than a linear scan?
nextOffset += 1
continue INNER
}
pos, nextAddr, v := curr.TransitionFor(t)
// the next slot in the statesStack might have an
// fstState instance that we can reuse
var nextPrealloc fstState
if len(i.statesStack) < cap(i.statesStack) {
nextPrealloc = i.statesStack[0:cap(i.statesStack)][len(i.statesStack)]
}
// push onto stack
next, err := i.f.decoder.stateAt(nextAddr, nextPrealloc)
if err != nil {
return err
}
i.statesStack = append(i.statesStack, next)
i.keysStack = append(i.keysStack, t)
i.keysPosStack = append(i.keysPosStack, pos)
i.valsStack = append(i.valsStack, v)
i.autStatesStack = append(i.autStatesStack, autNext)
nextOffset = 0
allowCompare = true
continue OUTER
}
// no more transitions, so need to backtrack and stack pop
if len(i.statesStack) <= 1 {
// stack len is 1 (root), can't go back further, we're done
break
}
// if the top of the stack represents a linear chain of states
// (i.e., a suffix of nodes linked by single transitions),
// then optimize by popping the suffix in one shot without
// going back all the way to the OUTER loop
var popNum int
for j := len(i.statesStack) - 1; j > 0; j-- {
if i.statesStack[j].NumTransitions() != 1 {
popNum = len(i.statesStack) - 1 - j
break
}
}
if popNum < 1 { // always pop at least 1 entry from the stacks
popNum = 1
}
nextOffset = i.keysPosStack[len(i.keysPosStack)-popNum] + 1
allowCompare = false
i.statesStack = i.statesStack[:len(i.statesStack)-popNum]
i.keysStack = i.keysStack[:len(i.keysStack)-popNum]
i.keysPosStack = i.keysPosStack[:len(i.keysPosStack)-popNum]
i.valsStack = i.valsStack[:len(i.valsStack)-popNum]
i.autStatesStack = i.autStatesStack[:len(i.autStatesStack)-popNum]
}
return ErrIteratorDone
}
// Seek advances this iterator to the specified key/value pair. If this key
// is not in the FST, Current() will return the next largest key. If this
// seek operation would go past the last key, or outside the configured
// startKeyInclusive/endKeyExclusive then ErrIteratorDone is returned.
func (i *FSTIterator) Seek(key []byte) error {
return i.pointTo(key)
}
// Close will free any resources held by this iterator.
func (i *FSTIterator) Close() error {
// at the moment we don't do anything,
// but wanted this for API completeness
return nil
}