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88 lines
2.5 KiB
Cython
88 lines
2.5 KiB
Cython
from libcpp.vector cimport vector
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from libc.stdint cimport uint32_t
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from libc.stdint cimport int64_t
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from libc.stdint cimport uint64_t
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import numpy
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cdef struct Node:
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float prob
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int left
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int right
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cpdef list huffman_encode(float[:] probs):
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assert len(probs) >= 3
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output = numpy.zeros(shape=(len(probs),), dtype=numpy.uint64)
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cdef int size = len(probs)
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cdef vector[Node] nodes
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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) < len(nodes):
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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 >= len(nodes):
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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 == len(nodes) 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) < len(nodes) 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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output = ['' for _ in range(len(probs))]
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assign_codes(nodes, output, len(nodes) - 1, b'')
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return output
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cdef int assign_codes(vector[Node]& nodes, list codes, int i, bytes path) except -1:
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left_path = path + b'0'
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right_path = path + b'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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codes[-(nodes[i].left + 1)] = 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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codes[-(nodes[i].right + 1)] = right_path
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cdef int cover_two_nodes(vector[Node]& nodes, int j) nogil:
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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) except -1:
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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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leaf_id = - <int64_t>(id_ + 1)
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new_prob = prob + nodes[j].prob
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if prob < nodes[j].prob:
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node = Node(left=leaf_id, right=j, prob=new_prob)
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else:
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node = Node(left=j, right=leaf_id, 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) except -1:
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cdef Node node = Node(left=-(id1 + 1), right=-(id2 + 1), prob=prob)
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nodes.push_back(node)
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