// Copyright 2016 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 kademlia
import (
"fmt"
"math/rand"
"strings"
"github.com/ethereum/go-ethereum/common"
)
type Address common.Hash
func (a Address) String() string {
return fmt.Sprintf("%x", a[:])
}
func (a *Address) MarshalJSON() (out []byte, err error) {
return []byte(`"` + a.String() + `"`), nil
}
func (a *Address) UnmarshalJSON(value []byte) error {
*a = Address(common.HexToHash(string(value[1 : len(value)-1])))
return nil
}
// the string form of the binary representation of an address (only first 8 bits)
func (a Address) Bin() string {
var bs []string
for _, b := range a[:] {
bs = append(bs, fmt.Sprintf("%08b", b))
}
return strings.Join(bs, "")
}
/*
Proximity(x, y) returns the proximity order of the MSB distance between x and y
The distance metric MSB(x, y) of two equal length byte sequences x and y is the
value of the binary integer cast of the x^y, ie., x and y bitwise xor-ed.
the binary cast is big endian: most significant bit first (=MSB).
Proximity(x, y) is a discrete logarithmic scaling of the MSB distance.
It is defined as the reverse rank of the integer part of the base 2
logarithm of the distance.
It is calculated by counting the number of common leading zeros in the (MSB)
binary representation of the x^y.
(0 farthest, 255 closest, 256 self)
*/
func proximity(one, other Address) (ret int) {
for i := 0; i < len(one); i++ {
oxo := one[i] ^ other[i]
for j := 0; j < 8; j++ {
if (oxo>>uint8(7-j))&0x01 != 0 {
return i*8 + j
}
}
}
return len(one) * 8
}
// Address.ProxCmp compares the distances a->target and b->target.
// Returns -1 if a is closer to target, 1 if b is closer to target
// and 0 if they are equal.
func (target Address) ProxCmp(a, b Address) int {
for i := range target {
da := a[i] ^ target[i]
db := b[i] ^ target[i]
if da > db {
return 1
} else if da < db {
return -1
}
}
return 0
}
// randomAddressAt(address, prox) generates a random address
// at proximity order prox relative to address
// if prox is negative a random address is generated
func RandomAddressAt(self Address, prox int) (addr Address) {
addr = self
var pos int
if prox >= 0 {
pos = prox / 8
trans := prox % 8
transbytea := byte(0)
for j := 0; j <= trans; j++ {
transbytea |= 1 << uint8(7-j)
}
flipbyte := byte(1 << uint8(7-trans))
transbyteb := transbytea ^ byte(255)
randbyte := byte(rand.Intn(255))
addr[pos] = ((addr[pos] & transbytea) ^ flipbyte) | randbyte&transbyteb
}
for i := pos + 1; i < len(addr); i++ {
addr[i] = byte(rand.Intn(255))
}
return
}
// KeyRange(a0, a1, proxLimit) returns the address inclusive address
// range that contain addresses closer to one than other
func KeyRange(one, other Address, proxLimit int) (start, stop Address) {
prox := proximity(one, other)
if prox >= proxLimit {
prox = proxLimit
}
start = CommonBitsAddrByte(one, other, byte(0x00), prox)
stop = CommonBitsAddrByte(one, other, byte(0xff), prox)
return
}
func CommonBitsAddrF(self, other Address, f func() byte, p int) (addr Address) {
prox := proximity(self, other)
var pos int
if p <= prox {
prox = p
}
pos = prox / 8
addr = self
trans := byte(prox % 8)
var transbytea byte
if p > prox {
transbytea = byte(0x7f)
} else {
transbytea = byte(0xff)
}
transbytea >>= trans
transbyteb := transbytea ^ byte(0xff)
addrpos := addr[pos]
addrpos &= transbyteb
if p > prox {
addrpos ^= byte(0x80 >> trans)
}
addrpos |= transbytea & f()
addr[pos] = addrpos
for i := pos + 1; i < len(addr); i++ {
addr[i] = f()
}
return
}
func CommonBitsAddr(self, other Address, prox int) (addr Address) {
return CommonBitsAddrF(self, other, func() byte { return byte(rand.Intn(255)) }, prox)
}
func CommonBitsAddrByte(self, other Address, b byte, prox int) (addr Address) {
return CommonBitsAddrF(self, other, func() byte { return b }, prox)
}
// randomAddressAt() generates a random address
func RandomAddress() Address {
return RandomAddressAt(Address{}, -1)
}
