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path: root/trie/encoding.go
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// 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

func compactEncode(hexSlice []byte) []byte {
    terminator := byte(0)
    if hexSlice[len(hexSlice)-1] == 16 {
        terminator = 1
        hexSlice = hexSlice[:len(hexSlice)-1]
    }
    var (
        odd    = byte(len(hexSlice) % 2)
        buflen = len(hexSlice)/2 + 1
        bi, hi = 0, 0    // indices
        hs     = byte(0) // shift: flips between 0 and 4
    )
    if odd == 0 {
        bi = 1
        hs = 4
    }
    buf := make([]byte, buflen)
    buf[0] = terminator<<5 | byte(odd)<<4
    for bi < len(buf) && hi < len(hexSlice) {
        buf[bi] |= hexSlice[hi] << hs
        if hs == 0 {
            bi++
        }
        hi, hs = hi+1, hs^(1<<2)
    }
    return buf
}

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 {
    l := len(str)*2 + 1
    var nibbles = make([]byte, l)
    for i, b := range str {
        nibbles[i*2] = b / 16
        nibbles[i*2+1] = b % 16
    }
    nibbles[l-1] = 16
    return nibbles
}

// compactHexEncode encodes a series of nibbles into a byte array
func compactHexEncode(nibbles []byte) []byte {
    nl := len(nibbles)
    if nl == 0 {
        return nil
    }
    if nibbles[nl-1] == 16 {
        nl--
    }
    l := (nl + 1) / 2
    var str = make([]byte, l)
    for i, _ := range str {
        b := nibbles[i*2] * 16
        if nl > i*2 {
            b += nibbles[i*2+1]
        }
        str[i] = b
    }
    return str
}

func decodeCompact(key []byte) []byte {
    l := len(key) / 2
    var res = make([]byte, l)
    for i := 0; i < l; i++ {
        v1, v0 := key[2*i], key[2*i+1]
        res[i] = v1*16 + v0
    }
    return res
}

// prefixLen returns the length of the common prefix of a and b.
func prefixLen(a, b []byte) int {
    var i, length = 0, len(a)
    if len(b) < length {
        length = len(b)
    }
    for ; i < length; i++ {
        if a[i] != b[i] {
            break
        }
    }
    return i
}

func hasTerm(s []byte) bool {
    return s[len(s)-1] == 16
}

func remTerm(s []byte) []byte {
    if hasTerm(s) {
        b := make([]byte, len(s)-1)
        copy(b, s)
        return b
    }
    return s
}