path: root/trie/encoding.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package trie

import (
    "bytes"
)

func CompactEncode(hexSlice []byte) []byte {
    terminator := 0
    if hexSlice[len(hexSlice)-1] == 16 {
        terminator = 1
    }

    if terminator == 1 {
        hexSlice = hexSlice[:len(hexSlice)-1]
    }

    oddlen := len(hexSlice) % 2
    flags := byte(2*terminator + oddlen)
    if oddlen != 0 {
        hexSlice = append([]byte{flags}, hexSlice...)
    } else {
        hexSlice = append([]byte{flags, 0}, hexSlice...)
    }

    var buff bytes.Buffer
    for i := 0; i < len(hexSlice); i += 2 {
        buff.WriteByte(byte(16*hexSlice[i] + hexSlice[i+1]))
    }

    return buff.Bytes()
}

func CompactDecode(str []byte) []byte {
    base := CompactHexDecode(str)
    base = base[:len(base)-1]
    if base[0] >= 2 {
        base = append(base, 16)
    }
    if base[0]%2 == 1 {
        base = base[1:]
    } else {
        base = base[2:]
    }

    return base
}

func CompactHexDecode(str []byte) []byte {
    var nibbles []byte

    for _, b := range str {
        nibbles = append(nibbles, b/16)
        nibbles = append(nibbles, b%16)
    }
    nibbles = append(nibbles, 16)
    return nibbles
}

// assumes key is odd length
func DecodeCompact(key []byte) []byte {
    var res []byte
    for i := 0; i < len(key)-1; i += 2 {
        v1, v0 := key[i], key[i+1]
        res = append(res, v1*16+v0)
    }
    return res
}