mirror of https://github.com/explosion/spaCy.git
158 lines
5.2 KiB
Cython
158 lines
5.2 KiB
Cython
cimport cython
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from .bits cimport bit_append
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from .bits cimport BitArray
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cdef class HuffmanCodec:
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"""Create a Huffman code table, and use it to pack and unpack sequences into
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byte strings. Emphasis is on efficiency, so API is quite strict:
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Messages will be encoded/decoded as indices that refer to the probability sequence.
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For instance, the sequence [5, 10, 8] indicates the 5th most frequent item,
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the 10th most frequent item, the 8th most frequent item.
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Arguments:
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weights (float[:]): A descending-sorted sequence of probabilities/weights.
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Must include a weight for an EOL symbol.
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eol (uint32_t): The index of the weight of the EOL symbol.
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"""
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def __init__(self, float[:] weights):
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self.codes.resize(len(weights))
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for i in range(len(self.codes)):
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self.codes[i].bits = 0
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self.codes[i].length = 0
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populate_nodes(self.nodes, weights)
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cdef Code path
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path.bits = 0
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path.length = 0
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assign_codes(self.nodes, self.codes, len(self.nodes) - 1, path)
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def encode(self, uint32_t[:] msg, BitArray into_bits):
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cdef uint32_t i
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for i in range(len(msg)):
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into_bits.extend(self.codes[msg[i]].bits, self.codes[msg[i]].length)
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def decode(self, bits, uint32_t[:] into_msg):
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node = self.nodes.back()
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cdef int i = 0
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cdef int n = len(into_msg)
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for bit in bits:
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branch = node.right if bit else node.left
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if branch >= 0:
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node = self.nodes.at(branch)
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else:
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into_msg[i] = -(branch + 1)
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node = self.nodes.back()
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i += 1
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if i == n:
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break
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else:
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raise Exception
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property strings:
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@cython.boundscheck(False)
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@cython.wraparound(False)
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@cython.nonecheck(False)
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def __get__(self):
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output = []
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cdef int i, j
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cdef bytes string
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cdef Code code
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for i in range(self.codes.size()):
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code = self.codes[i]
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string = b'{0:b}'.format(code.bits).rjust(code.length, '0')
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string = string[::-1]
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output.append(string)
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return output
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@cython.boundscheck(False)
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@cython.wraparound(False)
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@cython.nonecheck(False)
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cdef int populate_nodes(vector[Node]& nodes, float[:] probs) except -1:
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assert len(probs) >= 3
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cdef int size = len(probs)
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cdef int i = size - 1
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cdef int j = 0
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while i >= 0 or (j+1) < nodes.size():
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if i < 0:
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_cover_two_nodes(nodes, j)
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j += 2
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elif j >= nodes.size():
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_cover_two_words(nodes, i, i-1, probs[i] + probs[i-1])
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i -= 2
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elif i >= 1 and (j == nodes.size() or probs[i-1] < nodes[j].prob):
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_cover_two_words(nodes, i, i-1, probs[i] + probs[i-1])
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i -= 2
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elif (j+1) < nodes.size() and nodes[j+1].prob < probs[i]:
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_cover_two_nodes(nodes, j)
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j += 2
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else:
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_cover_one_word_one_node(nodes, j, i, probs[i])
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i -= 1
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j += 1
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return 0
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cdef int _cover_two_nodes(vector[Node]& nodes, int j) nogil:
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"""Introduce a new non-terminal, over two non-terminals)"""
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cdef Node node
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node.left = j
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node.right = j+1
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node.prob = nodes[j].prob + nodes[j+1].prob
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nodes.push_back(node)
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cdef int _cover_one_word_one_node(vector[Node]& nodes, int j, int id_, float prob) nogil:
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"""Introduce a new non-terminal, over one terminal and one non-terminal."""
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cdef Node node
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# Encode leaves as negative integers, where the integer is the index of the
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# word in the vocabulary.
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cdef int64_t leaf_id = - <int64_t>(id_ + 1)
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cdef float new_prob = prob + nodes[j].prob
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if prob < nodes[j].prob:
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node.left = leaf_id
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node.right = j
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node.prob = new_prob
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else:
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node.left = j
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node.right = leaf_id
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node.prob = new_prob
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nodes.push_back(node)
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cdef int _cover_two_words(vector[Node]& nodes, int id1, int id2, float prob) nogil:
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"""Introduce a new node, over two non-terminals."""
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cdef Node node
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node.left = -(id1+1)
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node.right = -(id2+1)
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node.prob = prob
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nodes.push_back(node)
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cdef int assign_codes(vector[Node]& nodes, vector[Code]& codes, int i, Code path) except -1:
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"""Recursively assign paths, from the top down. At the end, the entry codes[i]
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knows the bit-address of the node[j] that points to entry i in the vocabulary.
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So, to encode i, we go to codes[i] and read its bit-string. To decode, we
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navigate nodes recursively.
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"""
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cdef Code left_path = bit_append(path, 0)
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cdef Code right_path = bit_append(path, 1)
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# Assign down left branch
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if nodes[i].left >= 0:
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assign_codes(nodes, codes, nodes[i].left, left_path)
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else:
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# Leaf on left
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id_ = -(nodes[i].left + 1)
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codes[id_] = left_path
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# Assign down right branch
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if nodes[i].right >= 0:
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assign_codes(nodes, codes, nodes[i].right, right_path)
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else:
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# Leaf on right
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id_ = -(nodes[i].right + 1)
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codes[id_] = right_path
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