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