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// 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 (
"encoding/binary"
"fmt"
"io"
)
const headerSize = 16
type encoderConstructor func(w io.Writer) encoder
type decoderConstructor func([]byte) decoder
var encoders = map[int]encoderConstructor{}
var decoders = map[int]decoderConstructor{}
type encoder interface {
start() error
encodeState(s *builderNode, addr int) (int, error)
finish(count, rootAddr int) error
reset(w io.Writer)
}
func loadEncoder(ver int, w io.Writer) (encoder, error) {
if cons, ok := encoders[ver]; ok {
return cons(w), nil
}
return nil, fmt.Errorf("no encoder for version %d registered", ver)
}
func registerEncoder(ver int, cons encoderConstructor) {
encoders[ver] = cons
}
type decoder interface {
getRoot() int
getLen() int
stateAt(addr int, prealloc fstState) (fstState, error)
}
func loadDecoder(ver int, data []byte) (decoder, error) {
if cons, ok := decoders[ver]; ok {
return cons(data), nil
}
return nil, fmt.Errorf("no decoder for version %d registered", ver)
}
func registerDecoder(ver int, cons decoderConstructor) {
decoders[ver] = cons
}
func decodeHeader(header []byte) (ver int, typ int, err error) {
if len(header) < headerSize {
err = fmt.Errorf("invalid header < 16 bytes")
return
}
ver = int(binary.LittleEndian.Uint64(header[0:8]))
typ = int(binary.LittleEndian.Uint64(header[8:16]))
return
}
// fstState represents a state inside the FTS runtime
// It is the main contract between the FST impl and the decoder
// The FST impl should work only with this interface, while only the decoder
// impl knows the physical representation.
type fstState interface {
Address() int
Final() bool
FinalOutput() uint64
NumTransitions() int
TransitionFor(b byte) (int, int, uint64)
TransitionAt(i int) byte
}
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