147 lines
3.7 KiB
Python
147 lines
3.7 KiB
Python
# This file is derived from the GPL program "PyPE"
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#
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# Copyright (C) 2003-2006 Josiah Carlson
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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#
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"""
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Least recently used algorithm
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"""
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class Node:
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"""
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Node to be stored in the LRU structure
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"""
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def __init__(self, prev, value):
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self.prev = prev
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self.value = value
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self.next = None
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class LRU:
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"""
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Implementation of a length-limited O(1) LRU cache
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"""
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def __init__(self, count):
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self.count = max(count, 2)
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self.data = {}
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self.first = None
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self.last = None
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def __contains__(self, obj):
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"""
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Return True if the object is contained in the LRU
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"""
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return obj in self.data
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def __getitem__(self, obj):
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"""
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Return item assocated with Obj
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"""
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return self.data[obj].value[1]
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def __setitem__(self, obj, val):
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"""
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Set the item in the LRU, removing an old entry if needed
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"""
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if obj in self.data:
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del self[obj]
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nobj = Node(self.last, (obj, val))
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if self.first is None:
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self.first = nobj
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if self.last:
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self.last.next = nobj
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self.last = nobj
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self.data[obj] = nobj
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if len(self.data) > self.count:
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if self.first == self.last:
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self.first = None
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self.last = None
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return
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lnk = self.first
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lnk.next.prev = None
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self.first = lnk.next
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lnk.next = None
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del self.data[lnk.value[0]]
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del lnk
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def __delitem__(self, obj):
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"""
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Delete the object from the LRU
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"""
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nobj = self.data[obj]
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if nobj.prev:
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nobj.prev.next = nobj.next
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else:
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self.first = nobj.next
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if nobj.next:
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nobj.next.prev = nobj.prev
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else:
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self.last = nobj.prev
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del self.data[obj]
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def __iter__(self):
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"""
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Iterate over the LRU
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"""
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cur = self.first
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while cur is not None:
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cur2 = cur.next
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yield cur.value[1]
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cur = cur2
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raise StopIteration
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def iteritems(self):
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"""
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Return items in the LRU using a generator
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"""
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cur = self.first
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while cur is not None:
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cur2 = cur.next
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yield cur.value
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cur = cur2
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raise StopIteration
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def iterkeys(self):
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"""
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Return keys in the LRU using a generator
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"""
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return iter(self.data)
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def itervalues(self):
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"""
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Return items and keys in the LRU using a generator
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"""
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for data in self.iteritems():
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yield data[1]
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def keys(self):
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"""
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Return all keys
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"""
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return [data[0] for data in self.iteritems()]
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def values(self):
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"""
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Return all values
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"""
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return [data[1] for data in self.iteritems()]
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def items(self):
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"""
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Return all items
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"""
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return [data[0] for data in self.iteritems()]
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