mirror of https://github.com/python/cpython
Marc-Andre Lemburg <mal@lemburg.com>:
Perfect hash table generator. Outputs a Python extension module which provides access to the hash table (which is stored in static C data) using custom code. This module can currently only generates code for the ucnhash module, but can easily be adapted to produce perfect hash tables for other tasks where fast lookup in large tables is needed. By Bill Tutt.
This commit is contained in:
Marc-André Lemburg
parent
c5bb9c21fe
commit
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#!/usr/bin/env/python
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# perfect_hash.py
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#
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# Outputs C code for a minimal perfect hash.
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# The hash is produced using the algorithm described in
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# "Optimal algorithms for minimal perfect hashing",
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# G. Havas, B.S. Majewski. Available as a technical report
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# from the CS department, University of Queensland
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# (ftp://ftp.cs.uq.oz.au/).
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#
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# This is a modified version of Andrew Kuchling's code
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# (http://starship.python.net/crew/amk/python/code/perfect-hash.html)
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# and generates C fragments suitable for compilation as a Python
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# extension module.
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#
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# Difference between this algorithm and gperf:
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# Gperf will complete in finite time with a successful function,
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# or by giving up.
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# This algorithm may never complete, although it is extremely likely
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# when c >= 2.
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# The algorithm works like this:
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# 0) You have K keys, that you want to perfectly hash to a bunch
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# of hash values.
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#
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# 1) Choose a number N larger than K. This is the number of
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# vertices in a graph G, and also the size of the resulting table.
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#
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# 2) Pick two random hash functions f1, f2, that output values from
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# 0...N-1.
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#
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# 3) for key in keys:
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# h1 = f1(key) ; h2 = f2(key)
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# Draw an edge between vertices h1 and h2 of the graph.
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# Associate the desired hash value with that edge.
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#
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# 4) Check if G is acyclic; if not, go back to step 1 and pick a bigger N.
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#
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# 5) Assign values to each vertex such that, for each edge, you can
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# add the values for the two vertices and get the desired value
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# for that edge -- which is the desired hash key. This task is
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# dead easy, because the graph is acyclic. This is done by
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# picking a vertex V, and assigning it a value of 0. You then do a
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# depth-first search, assigning values to new vertices so that
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# they sum up properly.
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#
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# 6) f1, f2, and G now make up your perfect hash function.
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import sys, whrandom, string
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import pprint
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import perfhash
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import time
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class Hash:
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"""Random hash function
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For simplicity and speed, this doesn't implement any byte-level hashing
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scheme. Instead, a random string is generated and prefixing to
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str(key), and then Python's hashing function is used."""
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def __init__(self, N, caseInsensitive=0):
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self.N = N
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junk = ""
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for i in range(10):
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junk = junk + whrandom.choice(string.letters + string.digits)
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self.junk = junk
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self.caseInsensitive = caseInsensitive
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self.seed = perfhash.calcSeed(junk)
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def __call__(self, key):
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key = str(key)
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if self.caseInsensitive:
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key = string.upper(key)
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x = perfhash.hash(self.seed, len(self.junk), key) % self.N
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#h = hash(self.junk + key) % self.N
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#assert x == h
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return x
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def generate_code(self):
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s = """{
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register int len;
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register unsigned char *p;
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register long x;
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len = cch;
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p = (unsigned char *) key;
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x = %(junkSeed)d;
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while (--len >= 0)
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x = (1000003*x) ^ """ % \
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{
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"lenJunk" : len(self.junk),
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"junkSeed" : self.seed,
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}
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if self.caseInsensitive:
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s = s + "toupper(*(p++));"
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else:
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s = s + "*(p++);"
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s = s + """
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x ^= cch + %(lenJunk)d;
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if (x == -1)
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x = -2;
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x %%= k_cHashElements;
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/* ensure the returned value is positive so we mimic Python's %% operator */
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if (x < 0)
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x += k_cHashElements;
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return x;
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}
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""" % { "lenJunk" : len(self.junk),
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"junkSeed" : self.seed, }
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return s
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WHITE, GREY, BLACK = 0,1,2
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class Graph:
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"""Graph class. This class isn't particularly efficient or general,
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and only has the features I needed to implement this algorithm.
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num_vertices -- number of vertices
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edges -- maps 2-tuples of vertex numbers to the value for this
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edge. If there's an edge between v1 and v2 (v1<v2),
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(v1,v2) is a key and the value is the edge's value.
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reachable_list -- maps a vertex V to the list of vertices
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to which V is connected by edges. Used
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for traversing the graph.
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values -- numeric value for each vertex
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"""
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def __init__(self, num_vertices):
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self.num_vertices = num_vertices
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self.edges = {}
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self.reachable_list = {}
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self.values = [-1] * num_vertices
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def connect(self, vertex1, vertex2, value):
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"""Connect 'vertex1' and 'vertex2' with an edge, with associated
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value 'value'"""
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if vertex1 > vertex2: vertex1, vertex2 = vertex2, vertex1
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# if self.edges.has_key( (vertex1, vertex2) ):
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# raise ValueError, 'Collision: vertices already connected'
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self.edges[ (vertex1, vertex2) ] = value
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# Add vertices to each other's reachable list
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if not self.reachable_list.has_key( vertex1 ):
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self.reachable_list[ vertex1 ] = [vertex2]
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else:
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self.reachable_list[vertex1].append(vertex2)
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if not self.reachable_list.has_key( vertex2 ):
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self.reachable_list[ vertex2 ] = [vertex1]
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else:
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self.reachable_list[vertex2].append(vertex1)
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def get_edge_value(self, vertex1, vertex2):
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"""Retrieve the value corresponding to the edge between
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'vertex1' and 'vertex2'. Raises KeyError if no such edge"""
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if vertex1 > vertex2:
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vertex1, vertex2 = vertex2, vertex1
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return self.edges[ (vertex1, vertex2) ]
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def is_acyclic(self):
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"Returns true if the graph is acyclic, otherwise false"
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# This is done by doing a depth-first search of the graph;
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# painting each vertex grey and then black. If the DFS
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# ever finds a vertex that isn't white, there's a cycle.
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colour = {}
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for i in range(self.num_vertices): colour[i] = WHITE
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# Loop over all vertices, taking white ones as starting
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# points for a traversal.
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for i in range(self.num_vertices):
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if colour[i] == WHITE:
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# List of vertices to visit
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visit_list = [ (None,i) ]
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# Do a DFS
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while visit_list:
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# Colour this vertex grey.
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parent, vertex = visit_list[0] ; del visit_list[0]
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colour[vertex] = GREY
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# Make copy of list of neighbours, removing the vertex
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# we arrived here from.
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neighbours = self.reachable_list.get(vertex, []) [:]
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if parent in neighbours: neighbours.remove( parent )
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for neighbour in neighbours:
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if colour[neighbour] == WHITE:
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visit_list.insert(0, (vertex, neighbour) )
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elif colour[neighbour] != WHITE:
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# Aha! Already visited this node,
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# so the graph isn't acyclic.
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return 0
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colour[vertex] = BLACK
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# We got through, so the graph is acyclic.
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return 1
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def assign_values(self):
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"""Compute values for each vertex, so that they sum up
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properly to the associated value for each edge."""
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# Also done with a DFS; I simply copied the DFS code
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# from is_acyclic(). (Should generalize the logic so
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# one function could be used from both methods,
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# but I couldn't be bothered.)
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colour = {}
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for i in range(self.num_vertices): colour[i] = WHITE
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# Loop over all vertices, taking white ones as starting
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# points for a traversal.
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for i in range(self.num_vertices):
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if colour[i] == WHITE:
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# Set this vertex's value, arbitrarily, to zero.
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self.set_vertex_value( i, 0 )
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# List of vertices to visit
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visit_list = [ (None,i) ]
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# Do a DFS
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while visit_list:
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# Colour this vertex grey.
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parent, vertex = visit_list[0] ; del visit_list[0]
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colour[vertex] = GREY
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# Make copy of list of neighbours, removing the vertex
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# we arrived here from.
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neighbours = self.reachable_list.get(vertex, []) [:]
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if parent in neighbours: neighbours.remove( parent )
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for neighbour in self.reachable_list.get(vertex, []):
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edge_value = self.get_edge_value( vertex, neighbour )
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if colour[neighbour] == WHITE:
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visit_list.insert(0, (vertex, neighbour) )
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# Set new vertex's value to the desired
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# edge value, minus the value of the
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# vertex we came here from.
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new_val = (edge_value -
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self.get_vertex_value( vertex ) )
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self.set_vertex_value( neighbour,
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new_val % self.num_vertices)
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colour[vertex] = BLACK
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# Returns nothing
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return
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def __getitem__(self, index):
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if index < self.num_vertices: return index
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raise IndexError
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def get_vertex_value(self, vertex):
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"Get value for a vertex"
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return self.values[ vertex ]
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def set_vertex_value(self, vertex, value):
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"Set value for a vertex"
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self.values[ vertex ] = value
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def generate_code(self, out, width = 70):
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"Return nicely formatted table"
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out.write("{ ")
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pos = 0
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for v in self.values:
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v=str(v)+', '
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out.write(v)
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pos = pos + len(v) + 1
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if pos > width: out.write('\n '); pos = 0
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out.write('};\n')
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class PerfectHash:
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def __init__(self, cchMax, f1, f2, G, cHashElements, cKeys, maxHashValue):
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self.cchMax = cchMax
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self.f1 = f1
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self.f2 = f2
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self.G = G
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self.cHashElements = cHashElements
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self.cKeys = cKeys
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# determine the necessary type for storing our hash function
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# helper table:
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self.type = self.determineType(maxHashValue)
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def generate_header(self, structName):
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header = """
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#include <Python.h>
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#include <stdlib.h>
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/* --- C API ----------------------------------------------------*/
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/* C API for usage by other Python modules */
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typedef struct %(structName)s
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{
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unsigned long cKeys;
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unsigned long cchMax;
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unsigned long (*hash)(const char *key, unsigned int cch);
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const void *(*getValue)(unsigned long iKey);
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} %(structName)s;
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""" % { "structName" : structName }
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return header
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def determineType(self, maxHashValue):
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if maxHashValue <= 255:
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return "unsigned char"
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elif maxHashValue <= 65535:
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return "unsigned short"
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else:
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# Take the cheesy way out...
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return "unsigned long"
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def generate_code(self, moduleName, dataArrayName, dataArrayType, structName):
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# Output C code for the hash functions and tables
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code = """
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/*
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* The hash is produced using the algorithm described in
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* "Optimal algorithms for minimal perfect hashing",
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* G. Havas, B.S. Majewski. Available as a technical report
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* from the CS department, University of Queensland
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* (ftp://ftp.cs.uq.oz.au/).
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*
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* Generated using a heavily tweaked version of Andrew Kuchling's
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* perfect_hash.py:
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* http://starship.python.net/crew/amk/python/code/perfect-hash.html
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*
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* Generated on: %s
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*/
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""" % time.ctime(time.time())
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# MSVC SP3 was complaining when I actually used a global constant
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code = code + """
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#define k_cHashElements %i
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#define k_cchMaxKey %d
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#define k_cKeys %i
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""" % (self.cHashElements, self.cchMax, self.cKeys)
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code = code + """
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static const %s G[k_cHashElements];
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static const %s %s[k_cKeys];
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""" % (self.type, dataArrayType, dataArrayName)
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code = code + """
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static long f1(const char *key, unsigned int cch)
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"""
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code = code + self.f1.generate_code()
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code = code + """
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static long f2(const char *key, unsigned int cch)
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"""
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code = code + self.f2.generate_code()
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code = code + """
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static unsigned long hash(const char *key, unsigned int cch)
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{
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return ((unsigned long)(G[ f1(key, cch) ]) + (unsigned long)(G[ f2(key, cch) ]) ) %% k_cHashElements;
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}
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const void *getValue(unsigned long iKey)
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{
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return &%(dataArrayName)s[iKey];
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}
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/* Helper for adding objects to dictionaries. Check for errors with
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PyErr_Occurred() */
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static
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void insobj(PyObject *dict,
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char *name,
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PyObject *v)
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{
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PyDict_SetItemString(dict, name, v);
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Py_XDECREF(v);
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}
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static const %(structName)s hashAPI =
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{
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k_cKeys,
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k_cchMaxKey,
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&hash,
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&getValue,
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};
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static
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PyMethodDef Module_methods[] =
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{
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{NULL, NULL},
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};
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static char *Module_docstring = "%(moduleName)s hash function module";
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/* Error reporting for module init functions */
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#define Py_ReportModuleInitError(modname) { \\
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PyObject *exc_type, *exc_value, *exc_tb; \\
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PyObject *str_type, *str_value; \\
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\\
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/* Fetch error objects and convert them to strings */ \\
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PyErr_Fetch(&exc_type, &exc_value, &exc_tb); \\
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if (exc_type && exc_value) { \\
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str_type = PyObject_Str(exc_type); \\
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str_value = PyObject_Str(exc_value); \\
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} \\
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else { \\
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str_type = NULL; \\
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str_value = NULL; \\
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} \\
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/* Try to format a more informative error message using the \\
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original error */ \\
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if (str_type && str_value && \\
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PyString_Check(str_type) && PyString_Check(str_value)) \\
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PyErr_Format( \\
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PyExc_ImportError, \\
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"initialization of module "modname" failed " \\
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"(%%s:%%s)", \\
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PyString_AS_STRING(str_type), \\
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PyString_AS_STRING(str_value)); \\
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else \\
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PyErr_SetString( \\
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PyExc_ImportError, \\
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"initialization of module "modname" failed"); \\
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Py_XDECREF(str_type); \\
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Py_XDECREF(str_value); \\
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Py_XDECREF(exc_type); \\
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Py_XDECREF(exc_value); \\
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Py_XDECREF(exc_tb); \\
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}
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/* Create PyMethodObjects and register them in the module\'s dict */
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DL_EXPORT(void)
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init%(moduleName)s(void)
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{
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PyObject *module, *moddict;
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/* Create module */
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module = Py_InitModule4("%(moduleName)s", /* Module name */
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Module_methods, /* Method list */
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Module_docstring, /* Module doc-string */
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(PyObject *)NULL, /* always pass this as *self */
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PYTHON_API_VERSION); /* API Version */
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if (module == NULL)
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goto onError;
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/* Add some constants to the module\'s dict */
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moddict = PyModule_GetDict(module);
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if (moddict == NULL)
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goto onError;
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/* Export C API */
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insobj(
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moddict,
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"%(moduleName)sAPI",
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PyCObject_FromVoidPtr((void *)&hashAPI, NULL));
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onError:
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/* Check for errors and report them */
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if (PyErr_Occurred())
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Py_ReportModuleInitError("%(moduleName)s");
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return;
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}
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""" % { "moduleName" : moduleName,
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"dataArrayName" : dataArrayName,
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"structName" : structName, }
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return code
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def generate_graph(self, out):
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out.write("""
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static const unsigned short G[] =
|
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""")
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self.G.generate_code(out)
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def generate_hash(keys, caseInsensitive=0,
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minC=None, initC=None,
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f1Seed=None, f2Seed=None,
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cIncrement=None, cTries=None):
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"""Print out code for a perfect minimal hash. Input is a list of
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(key, desired hash value) tuples. """
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|
||||
# K is the number of keys.
|
||||
K = len(keys)
|
||||
|
||||
# We will be generating graphs of size N, where N = c * K.
|
||||
# The larger C is, the fewer trial graphs will need to be made, but
|
||||
# the resulting table is also larger. Increase this starting value
|
||||
# if you're impatient. After 50 failures, c will be increased by 0.025.
|
||||
if initC is None:
|
||||
initC = 1.5
|
||||
|
||||
c = initC
|
||||
if cIncrement is None:
|
||||
cIncrement = 0.0025
|
||||
|
||||
if cTries is None:
|
||||
cTries = 50
|
||||
|
||||
# Number of trial graphs so far
|
||||
num_graphs = 0
|
||||
sys.stderr.write('Generating graphs... ')
|
||||
|
||||
while 1:
|
||||
# N is the number of vertices in the graph G
|
||||
N = int(c*K)
|
||||
num_graphs = num_graphs + 1
|
||||
if (num_graphs % cTries) == 0:
|
||||
# Enough failures at this multiplier,
|
||||
# increase the multiplier and keep trying....
|
||||
c = c + cIncrement
|
||||
|
||||
# Whats good with searching for a better
|
||||
# hash function if we exceed the size
|
||||
# of a function we've generated in the past....
|
||||
if minC is not None and \
|
||||
c > minC:
|
||||
c = initC
|
||||
sys.stderr.write(' -- c > minC, resetting c to %0.4f\n' % c)
|
||||
else:
|
||||
sys.stderr.write(' -- increasing c to %0.4f\n' % c)
|
||||
sys.stderr.write('Generating graphs... ')
|
||||
|
||||
# Output a progress message
|
||||
sys.stderr.write( str(num_graphs) + ' ')
|
||||
sys.stderr.flush()
|
||||
|
||||
# Create graph w/ N vertices
|
||||
G = Graph(N)
|
||||
# Save the seeds used to generate
|
||||
# the following two hash functions.
|
||||
_seeds = whrandom._inst._seed
|
||||
|
||||
# Create 2 random hash functions
|
||||
f1 = Hash(N, caseInsensitive)
|
||||
f2 = Hash(N, caseInsensitive)
|
||||
|
||||
# Set the initial hash function seed values if passed in.
|
||||
# Doing this protects our hash functions from
|
||||
# changes to whrandom's behavior.
|
||||
if f1Seed is not None:
|
||||
f1.seed = f1Seed
|
||||
f1Seed = None
|
||||
fSpecifiedSeeds = 1
|
||||
if f2Seed is not None:
|
||||
f2.seed = f2Seed
|
||||
f2Seed = None
|
||||
fSpecifiedSeeds = 1
|
||||
|
||||
# Connect vertices given by the values of the two hash functions
|
||||
# for each key. Associate the desired hash value with each
|
||||
# edge.
|
||||
for k, v in keys:
|
||||
h1 = f1(k) ; h2 = f2(k)
|
||||
G.connect( h1,h2, v)
|
||||
|
||||
# Check if the resulting graph is acyclic; if it is,
|
||||
# we're done with step 1.
|
||||
if G.is_acyclic():
|
||||
break
|
||||
elif fSpecifiedSeeds:
|
||||
sys.stderr.write('\nThe initial f1/f2 seeds you specified didn\'t generate a perfect hash function: \n')
|
||||
sys.stderr.write('f1 seed: %s\n' % f1.seed)
|
||||
sys.stderr.write('f2 seed: %s\n' % f2.seed)
|
||||
sys.stderr.write('multipler: %s\n' % c)
|
||||
sys.stderr.write('Your data has likely changed, or you forgot what your initial multiplier should be.\n')
|
||||
sys.stderr.write('continuing the search for a perfect hash function......\n')
|
||||
fSpecifiedSeeds = 0
|
||||
|
||||
# Now we have an acyclic graph, so we assign values to each vertex
|
||||
# such that, for each edge, you can add the values for the two vertices
|
||||
# involved and get the desired value for that edge -- which is the
|
||||
# desired hash key. This task is dead easy, because the graph is acyclic.
|
||||
sys.stderr.write('\nAcyclic graph found; computing vertex values...\n')
|
||||
G.assign_values()
|
||||
|
||||
sys.stderr.write('Checking uniqueness of hash values...\n')
|
||||
|
||||
# Sanity check the result by actually verifying that all the keys
|
||||
# hash to the right value.
|
||||
cchMaxKey = 0
|
||||
maxHashValue = 0
|
||||
|
||||
for k, v in keys:
|
||||
hash1 = G.values[ f1(k) ]
|
||||
hash2 = G.values[ f2(k) ]
|
||||
if hash1 > maxHashValue:
|
||||
maxHashValue = hash1
|
||||
if hash2 > maxHashValue:
|
||||
maxHashValue = hash2
|
||||
perfecthash = (hash1 + hash2) % N
|
||||
assert perfecthash == v
|
||||
cch = len(k)
|
||||
if cch > cchMaxKey:
|
||||
cchMaxKey = cch
|
||||
|
||||
sys.stderr.write('Found perfect hash function!\n')
|
||||
sys.stderr.write('\nIn order to regenerate this hash function, \n')
|
||||
sys.stderr.write('you need to pass these following values back in:\n')
|
||||
sys.stderr.write('f1 seed: %s\n' % repr(f1.seed))
|
||||
sys.stderr.write('f2 seed: %s\n' % repr(f2.seed))
|
||||
sys.stderr.write('initial multipler: %s\n' % c)
|
||||
|
||||
return PerfectHash(cchMaxKey, f1, f2, G, N, len(keys), maxHashValue)
|
||||
|
||||
"""
|
||||
static
|
||||
PyObject *codec_tuple(PyObject *unicode,
|
||||
int len)
|
||||
{
|
||||
PyObject *v,*w;
|
||||
|
||||
if (unicode == NULL)
|
||||
return NULL;
|
||||
v = PyTuple_New(2);
|
||||
if (v == NULL) {
|
||||
Py_DECREF(unicode);
|
||||
return NULL;
|
||||
}
|
||||
PyTuple_SET_ITEM(v,0,unicode);
|
||||
w = PyInt_FromLong(len);
|
||||
if (w == NULL) {
|
||||
Py_DECREF(v);
|
||||
return NULL;
|
||||
}
|
||||
PyTuple_SET_ITEM(v,1,w);
|
||||
return v;
|
||||
}
|
||||
|
||||
static PyObject *
|
||||
ucn_decode(PyObject *self,
|
||||
PyObject *args)
|
||||
{
|
||||
const char *data;
|
||||
int size;
|
||||
const char *errors = NULL;
|
||||
PyObject *mapping = NULL;
|
||||
|
||||
if (!PyArg_ParseTuple(args, "t#|z:ucn_decode",
|
||||
&data, &size, &errors))
|
||||
return NULL;
|
||||
if (mapping == Py_None)
|
||||
mapping = NULL;
|
||||
|
||||
return codec_tuple(PyUnicode_DecodeNamedUnicodeEscape(data, size, errors),
|
||||
size);
|
||||
}
|
||||
|
||||
|
||||
static PyMethodDef _codecs_functions[] = {
|
||||
{ "ucn_decode", ucn_decode, 1 },
|
||||
};
|
||||
|
||||
DL_EXPORT(void)
|
||||
init_ucn()
|
||||
{
|
||||
Py_InitModule("_ucn", _codecs_functions);
|
||||
}
|
||||
|
||||
"""
|
||||
|
||||
|
||||
|
||||
Loading…
Reference in New Issue