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