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lucastheislucastheis
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add python interface
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‎python/__init__.py

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from warnings import warn
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from range_coder._range_coder import RangeEncoder, RangeDecoder # noqa: F401
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try:
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import numpy as np
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except ImportError:
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pass
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def prob_to_cum_freq(prob, resolution=1024):
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"""
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Converts probability distribution into a cumulative frequency table.
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Makes sure that non-zero probabilities are represented by non-zero frequencies,
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provided that :samp:`len({prob}) <= {resolution}`.
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Parameters
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----------
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prob : ndarray or list
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A one-dimensional array representing a probability distribution
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resolution : int
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Number of hypothetical samples used to generate integer frequencies
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Returns
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-------
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list
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Cumulative frequency table
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"""
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if len(prob) > resolution:
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warn('Resolution smaller than number of symbols.')
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prob = np.asarray(prob, dtype=np.float64)
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freq = np.zeros(prob.size, dtype=int)
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# this is similar to gradient descent in KL divergence (convex)
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with np.errstate(divide='ignore', invalid='ignore'):
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for _ in range(resolution):
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freq[np.nanargmax(prob / freq)] += 1
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return [0] + np.cumsum(freq).tolist()
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def cum_freq_to_prob(cumFreq):
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"""
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Converts a cumulative frequency table into a probability distribution.
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Parameters
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----------
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cumFreq : list
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Cumulative frequency table
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Returns
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-------
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ndarray
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Probability distribution
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"""
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return np.diff(cumFreq).astype(np.float64) / cumFreq[-1]

‎python/src/module.cpp

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#include <Python.h>
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#include "range_coder_interface.h"
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static PyMethodDef RangeEncoder_methods[] = {
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{"encode",
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(PyCFunction)RangeEncoder_encode,
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METH_VARARGS | METH_KEYWORDS,
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RangeEncoder_encode_doc},
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{"close",
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(PyCFunction)RangeEncoder_close,
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METH_VARARGS | METH_KEYWORDS,
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RangeEncoder_close_doc},
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{0}
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};
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static PyGetSetDef RangeEncoder_getset[] = {
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{0}
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};
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PyTypeObject RangeEncoder_type = {
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PyVarObject_HEAD_INIT(0, 0)
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"range_coder.RangeEncoder", /*tp_name*/
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sizeof(RangeEncoderObject), /*tp_basicsize*/
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0, /*tp_itemsize*/
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(destructor)RangeEncoder_dealloc, /*tp_dealloc*/
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0, /*tp_print*/
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0, /*tp_getattr*/
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0, /*tp_setattr*/
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0, /*tp_compare*/
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0, /*tp_repr*/
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0, /*tp_as_number*/
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0, /*tp_as_sequence*/
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0, /*tp_as_mapping*/
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0, /*tp_hash */
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0, /*tp_call*/
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0, /*tp_str*/
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0, /*tp_getattro*/
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT, /*tp_flags*/
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RangeEncoder_doc, /*tp_doc*/
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0, /*tp_traverse*/
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0, /*tp_clear*/
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0, /*tp_richcompare*/
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0, /*tp_weaklistoffset*/
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0, /*tp_iter*/
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0, /*tp_iternext*/
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RangeEncoder_methods, /*tp_methods*/
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0, /*tp_members*/
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RangeEncoder_getset, /*tp_getset*/
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0, /*tp_base*/
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0, /*tp_dict*/
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0, /*tp_descr_get*/
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0, /*tp_descr_set*/
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0, /*tp_dictoffset*/
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(initproc)RangeEncoder_init, /*tp_init*/
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0, /*tp_alloc*/
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RangeEncoder_new, /*tp_new*/
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};
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static PyMethodDef RangeDecoder_methods[] = {
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{"decode",
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(PyCFunction)RangeDecoder_decode,
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METH_VARARGS | METH_KEYWORDS,
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RangeDecoder_decode_doc},
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{"close",
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(PyCFunction)RangeDecoder_close,
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METH_VARARGS | METH_KEYWORDS,
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RangeDecoder_close_doc},
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{0}
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};
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static PyGetSetDef RangeDecoder_getset[] = {
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{0}
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};
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PyTypeObject RangeDecoder_type = {
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PyVarObject_HEAD_INIT(0, 0)
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"range_coder.RangeDecoder", /*tp_name*/
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sizeof(RangeDecoderObject), /*tp_basicsize*/
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0, /*tp_itemsize*/
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(destructor)RangeDecoder_dealloc, /*tp_dealloc*/
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0, /*tp_print*/
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0, /*tp_getattr*/
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0, /*tp_setattr*/
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0, /*tp_compare*/
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0, /*tp_repr*/
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0, /*tp_as_number*/
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0, /*tp_as_sequdece*/
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0, /*tp_as_mapping*/
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0, /*tp_hash */
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0, /*tp_call*/
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0, /*tp_str*/
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0, /*tp_getattro*/
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT, /*tp_flags*/
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RangeDecoder_doc, /*tp_doc*/
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0, /*tp_traverse*/
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0, /*tp_clear*/
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0, /*tp_richcompare*/
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0, /*tp_weaklistoffset*/
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0, /*tp_iter*/
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0, /*tp_iternext*/
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RangeDecoder_methods, /*tp_methods*/
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0, /*tp_members*/
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RangeDecoder_getset, /*tp_getset*/
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0, /*tp_base*/
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0, /*tp_dict*/
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0, /*tp_descr_get*/
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0, /*tp_descr_set*/
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0, /*tp_dictoffset*/
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(initproc)RangeDecoder_init, /*tp_init*/
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0, /*tp_alloc*/
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RangeDecoder_new, /*tp_new*/
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};
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#if PY_MAJOR_VERSION >= 3
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static PyModuleDef range_coder_module = {
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PyModuleDef_HEAD_INIT,
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"_range_coder",
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"A fast implementation of a range encoder and decoder."
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-1, 0, 0, 0, 0, 0
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};
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#endif
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#if PY_MAJOR_VERSION >= 3
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PyMODINIT_FUNC PyInit__range_coder() {
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// create module object
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PyObject* module = PyModule_Create(&range_coder_module);
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#define RETVAL 0;
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#else
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PyMODINIT_FUNC init_range_coder() {
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PyObject* module = Py_InitModule3(
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"_range_coder", 0, "A fast implementation of a range encoder and decoder.");
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#define RETVAL void();
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#endif
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if(!module)
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return RETVAL;
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// initialize types
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if(PyType_Ready(&RangeEncoder_type) < 0)
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return RETVAL;
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if(PyType_Ready(&RangeDecoder_type) < 0)
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return RETVAL;
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// add types to module
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Py_INCREF(&RangeEncoder_type);
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PyModule_AddObject(module, "RangeEncoder", reinterpret_cast<PyObject*>(&RangeEncoder_type));
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Py_INCREF(&RangeDecoder_type);
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PyModule_AddObject(module, "RangeDecoder", reinterpret_cast<PyObject*>(&RangeDecoder_type));
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#if PY_MAJOR_VERSION >= 3
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return module;
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#endif
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}

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