github.com/ethereumproject/go-ethereum@v5.5.2+incompatible/p2p/discover/distance.go (about)

     1  // Copyright 2015 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 discover
    18  
    19  import (
    20  	"sort"
    21  
    22  	"github.com/ethereumproject/go-ethereum/common"
    23  )
    24  
    25  // node distance computation.
    26  
    27  // Closest sorts a set on distance to Target.
    28  type closest struct {
    29  	Nodes  [bucketSize]*Node
    30  	Target common.Hash
    31  }
    32  
    33  func (c *closest) Slice() []*Node {
    34  	for i, n := range c.Nodes {
    35  		if n == nil {
    36  			return c.Nodes[:i]
    37  		}
    38  	}
    39  	return c.Nodes[:]
    40  }
    41  
    42  func (c *closest) Add(entry *Node) {
    43  	i := sort.Search(len(c.Nodes), func(i int) bool {
    44  		other := c.Nodes[i]
    45  		if other == nil {
    46  			return true
    47  		}
    48  		return distcmp(c.Target, other.sha, entry.sha) >= 0
    49  	})
    50  
    51  	if i >= len(c.Nodes) {
    52  		return
    53  	}
    54  	if n := c.Nodes[i]; n != nil && n.ID == entry.ID {
    55  		return
    56  	}
    57  
    58  	copy(c.Nodes[i+1:], c.Nodes[i:])
    59  	c.Nodes[i] = entry
    60  }
    61  
    62  // distcmp compares the distances a->target and b->target.
    63  // Returns -1 if a is closer to target, 1 if b is closer to target
    64  // and 0 if they are equal.
    65  func distcmp(target, a, b common.Hash) int {
    66  	for i := range target {
    67  		da := a[i] ^ target[i]
    68  		db := b[i] ^ target[i]
    69  		if da > db {
    70  			return 1
    71  		} else if da < db {
    72  			return -1
    73  		}
    74  	}
    75  	return 0
    76  }
    77  
    78  // table of leading zero counts for bytes [0..255]
    79  var lzcount = [256]int{
    80  	8, 7, 6, 6, 5, 5, 5, 5,
    81  	4, 4, 4, 4, 4, 4, 4, 4,
    82  	3, 3, 3, 3, 3, 3, 3, 3,
    83  	3, 3, 3, 3, 3, 3, 3, 3,
    84  	2, 2, 2, 2, 2, 2, 2, 2,
    85  	2, 2, 2, 2, 2, 2, 2, 2,
    86  	2, 2, 2, 2, 2, 2, 2, 2,
    87  	2, 2, 2, 2, 2, 2, 2, 2,
    88  	1, 1, 1, 1, 1, 1, 1, 1,
    89  	1, 1, 1, 1, 1, 1, 1, 1,
    90  	1, 1, 1, 1, 1, 1, 1, 1,
    91  	1, 1, 1, 1, 1, 1, 1, 1,
    92  	1, 1, 1, 1, 1, 1, 1, 1,
    93  	1, 1, 1, 1, 1, 1, 1, 1,
    94  	1, 1, 1, 1, 1, 1, 1, 1,
    95  	1, 1, 1, 1, 1, 1, 1, 1,
    96  	0, 0, 0, 0, 0, 0, 0, 0,
    97  	0, 0, 0, 0, 0, 0, 0, 0,
    98  	0, 0, 0, 0, 0, 0, 0, 0,
    99  	0, 0, 0, 0, 0, 0, 0, 0,
   100  	0, 0, 0, 0, 0, 0, 0, 0,
   101  	0, 0, 0, 0, 0, 0, 0, 0,
   102  	0, 0, 0, 0, 0, 0, 0, 0,
   103  	0, 0, 0, 0, 0, 0, 0, 0,
   104  	0, 0, 0, 0, 0, 0, 0, 0,
   105  	0, 0, 0, 0, 0, 0, 0, 0,
   106  	0, 0, 0, 0, 0, 0, 0, 0,
   107  	0, 0, 0, 0, 0, 0, 0, 0,
   108  	0, 0, 0, 0, 0, 0, 0, 0,
   109  	0, 0, 0, 0, 0, 0, 0, 0,
   110  	0, 0, 0, 0, 0, 0, 0, 0,
   111  	0, 0, 0, 0, 0, 0, 0, 0,
   112  }
   113  
   114  // logdist returns the logarithmic distance between a and b, log2(a ^ b).
   115  func logdist(a, b common.Hash) int {
   116  	lz := 0
   117  	for i := range a {
   118  		x := a[i] ^ b[i]
   119  		if x == 0 {
   120  			lz += 8
   121  		} else {
   122  			lz += lzcount[x]
   123  			break
   124  		}
   125  	}
   126  	return len(a)*8 - lz
   127  }