```
# -*- coding: utf-8 -*-
"""
Contains generic utillity functions used in various different parts of
Drogulus.
"""
# Copyright (C) 2012-2013 Nicholas H.Tollervey.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program 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 Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
from constants import K
[docs]def long_to_hex(raw):
"""
Given a raw numeric value (like a node's ID for example) returns it
expressed as a hexadecimal string.
"""
# Turn it into hex string (remembering to drop the '0x' at the start).
as_hex = hex(raw)[2:]
# If the integer is 'long' knock off the 'L'.
if as_hex[-1] == 'L':
as_hex = as_hex[:-1]
# If required, correct length by appending 'padding' zeros.
if len(as_hex) % 2 != 0:
as_hex = '0' + as_hex
as_hex = as_hex.decode('hex')
return as_hex
[docs]def hex_to_long(raw):
"""
Given a hexadecimal string representation of a number (like a key or
node's ID for example) returns the numeric (long) value.
"""
return long(raw.encode('hex'), 16)
[docs]def distance(key_one, key_two):
"""
Calculate the XOR result between two string variables returned as a long
type value.
"""
val_key_one = hex_to_long(key_one)
val_key_two = hex_to_long(key_two)
return val_key_one ^ val_key_two
[docs]def sort_contacts(contacts, target_key):
"""
Given a list of contacts, efficiently sorts it so that the contacts closest
to the target key are at the head. If the list is longer than K then only
the K closest contacts will be returned.
"""
# Key function
def node_key(node):
"""
Returns the node's distance to the target key.
"""
return distance(node.id, target_key)
contacts.sort(key=node_key)
return contacts[:K]
```

© Copyright 2012-2013, Nicholas H.Tollervey.

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