github.com/avence12/go-ethereum@v1.5.10-0.20170320123548-1dfd65f6d047/trie/encoding.go (about)

     1  // Copyright 2014 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  package trie
    18  
    19  func compactEncode(hexSlice []byte) []byte {
    20  	terminator := byte(0)
    21  	if hexSlice[len(hexSlice)-1] == 16 {
    22  		terminator = 1
    23  		hexSlice = hexSlice[:len(hexSlice)-1]
    24  	}
    25  	var (
    26  		odd    = byte(len(hexSlice) % 2)
    27  		buflen = len(hexSlice)/2 + 1
    28  		bi, hi = 0, 0    // indices
    29  		hs     = byte(0) // shift: flips between 0 and 4
    30  	)
    31  	if odd == 0 {
    32  		bi = 1
    33  		hs = 4
    34  	}
    35  	buf := make([]byte, buflen)
    36  	buf[0] = terminator<<5 | byte(odd)<<4
    37  	for bi < len(buf) && hi < len(hexSlice) {
    38  		buf[bi] |= hexSlice[hi] << hs
    39  		if hs == 0 {
    40  			bi++
    41  		}
    42  		hi, hs = hi+1, hs^(1<<2)
    43  	}
    44  	return buf
    45  }
    46  
    47  func compactDecode(str []byte) []byte {
    48  	base := compactHexDecode(str)
    49  	base = base[:len(base)-1]
    50  	if base[0] >= 2 {
    51  		base = append(base, 16)
    52  	}
    53  	if base[0]%2 == 1 {
    54  		base = base[1:]
    55  	} else {
    56  		base = base[2:]
    57  	}
    58  	return base
    59  }
    60  
    61  func compactHexDecode(str []byte) []byte {
    62  	l := len(str)*2 + 1
    63  	var nibbles = make([]byte, l)
    64  	for i, b := range str {
    65  		nibbles[i*2] = b / 16
    66  		nibbles[i*2+1] = b % 16
    67  	}
    68  	nibbles[l-1] = 16
    69  	return nibbles
    70  }
    71  
    72  // compactHexEncode encodes a series of nibbles into a byte array
    73  func compactHexEncode(nibbles []byte) []byte {
    74  	nl := len(nibbles)
    75  	if nl == 0 {
    76  		return nil
    77  	}
    78  	if nibbles[nl-1] == 16 {
    79  		nl--
    80  	}
    81  	l := (nl + 1) / 2
    82  	var str = make([]byte, l)
    83  	for i := range str {
    84  		b := nibbles[i*2] * 16
    85  		if nl > i*2 {
    86  			b += nibbles[i*2+1]
    87  		}
    88  		str[i] = b
    89  	}
    90  	return str
    91  }
    92  
    93  func decodeCompact(key []byte) []byte {
    94  	l := len(key) / 2
    95  	var res = make([]byte, l)
    96  	for i := 0; i < l; i++ {
    97  		v1, v0 := key[2*i], key[2*i+1]
    98  		res[i] = v1*16 + v0
    99  	}
   100  	return res
   101  }
   102  
   103  // prefixLen returns the length of the common prefix of a and b.
   104  func prefixLen(a, b []byte) int {
   105  	var i, length = 0, len(a)
   106  	if len(b) < length {
   107  		length = len(b)
   108  	}
   109  	for ; i < length; i++ {
   110  		if a[i] != b[i] {
   111  			break
   112  		}
   113  	}
   114  	return i
   115  }
   116  
   117  func hasTerm(s []byte) bool {
   118  	return s[len(s)-1] == 16
   119  }
   120  
   121  func remTerm(s []byte) []byte {
   122  	if hasTerm(s) {
   123  		b := make([]byte, len(s)-1)
   124  		copy(b, s)
   125  		return b
   126  	}
   127  	return s
   128  }