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198 lines
5.3 KiB
Go
198 lines
5.3 KiB
Go
// Copyright 2015 PingCAP, 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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// See the License for the specific language governing permissions and
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// limitations under the License.
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package codec
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import (
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"bytes"
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"encoding/binary"
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"runtime"
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"unsafe"
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"github.com/juju/errors"
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)
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const (
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encGroupSize = 8
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encMarker = byte(0xFF)
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encPad = byte(0x0)
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)
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var (
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pads = make([]byte, encGroupSize)
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encPads = []byte{encPad}
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)
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// EncodeBytes guarantees the encoded value is in ascending order for comparison,
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// encoding with the following rule:
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// [group1][marker1]...[groupN][markerN]
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// group is 8 bytes slice which is padding with 0.
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// marker is `0xFF - padding 0 count`
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// For example:
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// [] -> [0, 0, 0, 0, 0, 0, 0, 0, 247]
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// [1, 2, 3] -> [1, 2, 3, 0, 0, 0, 0, 0, 250]
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// [1, 2, 3, 0] -> [1, 2, 3, 0, 0, 0, 0, 0, 251]
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// [1, 2, 3, 4, 5, 6, 7, 8] -> [1, 2, 3, 4, 5, 6, 7, 8, 255, 0, 0, 0, 0, 0, 0, 0, 0, 247]
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// Refer: https://github.com/facebook/mysql-5.6/wiki/MyRocks-record-format#memcomparable-format
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func EncodeBytes(b []byte, data []byte) []byte {
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// Allocate more space to avoid unnecessary slice growing.
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// Assume that the byte slice size is about `(len(data) / encGroupSize + 1) * (encGroupSize + 1)` bytes,
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// that is `(len(data) / 8 + 1) * 9` in our implement.
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dLen := len(data)
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reallocSize := (dLen/encGroupSize + 1) * (encGroupSize + 1)
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result := reallocBytes(b, reallocSize)
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for idx := 0; idx <= dLen; idx += encGroupSize {
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remain := dLen - idx
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padCount := 0
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if remain >= encGroupSize {
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result = append(result, data[idx:idx+encGroupSize]...)
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} else {
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padCount = encGroupSize - remain
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result = append(result, data[idx:]...)
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result = append(result, pads[:padCount]...)
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}
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marker := encMarker - byte(padCount)
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result = append(result, marker)
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}
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return result
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}
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func decodeBytes(b []byte, reverse bool) ([]byte, []byte, error) {
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data := make([]byte, 0, len(b))
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for {
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if len(b) < encGroupSize+1 {
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return nil, nil, errors.New("insufficient bytes to decode value")
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}
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groupBytes := b[:encGroupSize+1]
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if reverse {
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reverseBytes(groupBytes)
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}
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group := groupBytes[:encGroupSize]
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marker := groupBytes[encGroupSize]
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// Check validity of marker.
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padCount := encMarker - marker
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realGroupSize := encGroupSize - padCount
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if padCount > encGroupSize {
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return nil, nil, errors.Errorf("invalid marker byte, group bytes %q", groupBytes)
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}
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data = append(data, group[:realGroupSize]...)
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b = b[encGroupSize+1:]
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if marker != encMarker {
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// Check validity of padding bytes.
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if bytes.Count(group[realGroupSize:], encPads) != int(padCount) {
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return nil, nil, errors.Errorf("invalid padding byte, group bytes %q", groupBytes)
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}
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break
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}
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}
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return b, data, nil
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}
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// DecodeBytes decodes bytes which is encoded by EncodeBytes before,
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// returns the leftover bytes and decoded value if no error.
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func DecodeBytes(b []byte) ([]byte, []byte, error) {
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return decodeBytes(b, false)
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}
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// EncodeBytesDesc first encodes bytes using EncodeBytes, then bitwise reverses
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// encoded value to guarantee the encoded value is in descending order for comparison.
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func EncodeBytesDesc(b []byte, data []byte) []byte {
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n := len(b)
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b = EncodeBytes(b, data)
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reverseBytes(b[n:])
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return b
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}
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// DecodeBytesDesc decodes bytes which is encoded by EncodeBytesDesc before,
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// returns the leftover bytes and decoded value if no error.
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func DecodeBytesDesc(b []byte) ([]byte, []byte, error) {
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return decodeBytes(b, true)
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}
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// EncodeCompactBytes joins bytes with its length into a byte slice. It is more
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// efficient in both space and time compare to EncodeBytes. Note that the encoded
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// result is not memcomparable.
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func EncodeCompactBytes(b []byte, data []byte) []byte {
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b = reallocBytes(b, binary.MaxVarintLen64+len(data))
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b = EncodeVarint(b, int64(len(data)))
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return append(b, data...)
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}
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// DecodeCompactBytes decodes bytes which is encoded by EncodeCompactBytes before.
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func DecodeCompactBytes(b []byte) ([]byte, []byte, error) {
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b, n, err := DecodeVarint(b)
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if err != nil {
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return nil, nil, errors.Trace(err)
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}
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if int64(len(b)) < n {
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return nil, nil, errors.Errorf("insufficient bytes to decode value, expected length: %v", n)
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}
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return b[n:], b[:n], nil
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}
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// See https://golang.org/src/crypto/cipher/xor.go
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const wordSize = int(unsafe.Sizeof(uintptr(0)))
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const supportsUnaligned = runtime.GOARCH == "386" || runtime.GOARCH == "amd64"
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func fastReverseBytes(b []byte) {
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n := len(b)
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w := n / wordSize
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if w > 0 {
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bw := *(*[]uintptr)(unsafe.Pointer(&b))
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for i := 0; i < w; i++ {
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bw[i] = ^bw[i]
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}
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}
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for i := w * wordSize; i < n; i++ {
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b[i] = ^b[i]
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}
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}
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func safeReverseBytes(b []byte) {
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for i := range b {
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b[i] = ^b[i]
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}
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}
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func reverseBytes(b []byte) {
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if supportsUnaligned {
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fastReverseBytes(b)
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return
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}
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safeReverseBytes(b)
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}
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// like realloc.
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func reallocBytes(b []byte, n int) []byte {
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newSize := len(b) + n
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if cap(b) < newSize {
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bs := make([]byte, len(b), newSize)
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copy(bs, b)
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return bs
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}
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// slice b has capability to store n bytes
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return b
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}
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