Add python interface

LICENSE

@@ -0,0 +1,15 @@
+Copyright (c) 2006, Daisuke Okanohara
+Copyright (c) 2008-2010, Cybozu Labs, Inc.
+Copyright (c) 2017-2023, Lucas Theis
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+

README.md

@@ -0,0 +1,28 @@
+Installation
+============
+
+	pip install range-coder
+
+
+Example
+=======
+
+```python
+from range_coder import RangeEncoder, RangeDecoder, prob_to_cum_freq
+
+data = [2, 0, 1, 0, 0, 0, 1, 2, 2]
+prob = [0.5, 0.2, 0.3]
+
+# convert probabilities to cumulative integer frequency table
+cumFreq = prob_to_cum_freq(prob, resolution=128)
+
+# encode data
+encoder = RangeEncoder(filepath)
+encoder.encode(data, cumFreq)
+encoder.close()
+
+# decode data
+decoder = RangeDecoder(filepath)
+dataRec = decoder.decode(len(data), cumFreq)
+decoder.close()
+```

python/__init__.py

@@ -0,0 +1,59 @@
+from warnings import warn
+from range_coder._range_coder import RangeEncoder, RangeDecoder  # noqa: F401
+
+try:
+    import numpy as np
+except ImportError:
+    pass
+
+
+def prob_to_cum_freq(prob, resolution=1024):
+    """
+    Converts probability distribution into a cumulative frequency table.
+
+    Makes sure that non-zero probabilities are represented by non-zero frequencies,
+    provided that :samp:`len({prob}) <= {resolution}`.
+
+    Parameters
+    ----------
+    prob : ndarray or list
+        A one-dimensional array representing a probability distribution
+
+    resolution : int
+        Number of hypothetical samples used to generate integer frequencies
+
+    Returns
+    -------
+    list
+        Cumulative frequency table
+    """
+
+    if len(prob) > resolution:
+        warn('Resolution smaller than number of symbols.')
+
+    prob = np.asarray(prob, dtype=np.float64)
+    freq = np.zeros(prob.size, dtype=int)
+
+    # this is similar to gradient descent in KL divergence (convex)
+    with np.errstate(divide='ignore', invalid='ignore'):
+        for _ in range(resolution):
+            freq[np.nanargmax(prob / freq)] += 1
+
+    return [0] + np.cumsum(freq).tolist()
+
+
+def cum_freq_to_prob(cumFreq):
+    """
+    Converts a cumulative frequency table into a probability distribution.
+
+    Parameters
+    ----------
+    cumFreq : list
+        Cumulative frequency table
+
+    Returns
+    -------
+    ndarray
+        Probability distribution
+    """
+    return np.diff(cumFreq).astype(np.float64) / cumFreq[-1]

python/src/module.cpp

@@ -0,0 +1,162 @@
+#include <Python.h>
+#include "range_coder_interface.h"
+
+static PyMethodDef RangeEncoder_methods[] = {
+	{"encode",
+		(PyCFunction)RangeEncoder_encode,
+		METH_VARARGS | METH_KEYWORDS,
+		RangeEncoder_encode_doc},
+	{"close",
+		(PyCFunction)RangeEncoder_close,
+		METH_VARARGS | METH_KEYWORDS,
+		RangeEncoder_close_doc},
+	{0}
+};
+
+
+static PyGetSetDef RangeEncoder_getset[] = {
+	{0}
+};
+
+
+PyTypeObject RangeEncoder_type = {
+	PyVarObject_HEAD_INIT(0, 0)
+	"range_coder.RangeEncoder",       /*tp_name*/
+	sizeof(RangeEncoderObject),       /*tp_basicsize*/
+	0,                                /*tp_itemsize*/
+	(destructor)RangeEncoder_dealloc, /*tp_dealloc*/
+	0,                                /*tp_print*/
+	0,                                /*tp_getattr*/
+	0,                                /*tp_setattr*/
+	0,                                /*tp_compare*/
+	0,                                /*tp_repr*/
+	0,                                /*tp_as_number*/
+	0,                                /*tp_as_sequence*/
+	0,                                /*tp_as_mapping*/
+	0,                                /*tp_hash */
+	0,                                /*tp_call*/
+	0,                                /*tp_str*/
+	0,                                /*tp_getattro*/
+	0,                                /*tp_setattro*/
+	0,                                /*tp_as_buffer*/
+	Py_TPFLAGS_DEFAULT,               /*tp_flags*/
+	RangeEncoder_doc,                 /*tp_doc*/
+	0,                                /*tp_traverse*/
+	0,                                /*tp_clear*/
+	0,                                /*tp_richcompare*/
+	0,                                /*tp_weaklistoffset*/
+	0,                                /*tp_iter*/
+	0,                                /*tp_iternext*/
+	RangeEncoder_methods,             /*tp_methods*/
+	0,                                /*tp_members*/
+	RangeEncoder_getset,              /*tp_getset*/
+	0,                                /*tp_base*/
+	0,                                /*tp_dict*/
+	0,                                /*tp_descr_get*/
+	0,                                /*tp_descr_set*/
+	0,                                /*tp_dictoffset*/
+	(initproc)RangeEncoder_init,      /*tp_init*/
+	0,                                /*tp_alloc*/
+	RangeEncoder_new,                 /*tp_new*/
+};
+
+static PyMethodDef RangeDecoder_methods[] = {
+	{"decode",
+		(PyCFunction)RangeDecoder_decode,
+		METH_VARARGS | METH_KEYWORDS,
+		RangeDecoder_decode_doc},
+	{"close",
+		(PyCFunction)RangeDecoder_close,
+		METH_VARARGS | METH_KEYWORDS,
+		RangeDecoder_close_doc},
+	{0}
+};
+
+
+static PyGetSetDef RangeDecoder_getset[] = {
+	{0}
+};
+
+
+PyTypeObject RangeDecoder_type = {
+	PyVarObject_HEAD_INIT(0, 0)
+	"range_coder.RangeDecoder",       /*tp_name*/
+	sizeof(RangeDecoderObject),       /*tp_basicsize*/
+	0,                                /*tp_itemsize*/
+	(destructor)RangeDecoder_dealloc, /*tp_dealloc*/
+	0,                                /*tp_print*/
+	0,                                /*tp_getattr*/
+	0,                                /*tp_setattr*/
+	0,                                /*tp_compare*/
+	0,                                /*tp_repr*/
+	0,                                /*tp_as_number*/
+	0,                                /*tp_as_sequdece*/
+	0,                                /*tp_as_mapping*/
+	0,                                /*tp_hash */
+	0,                                /*tp_call*/
+	0,                                /*tp_str*/
+	0,                                /*tp_getattro*/
+	0,                                /*tp_setattro*/
+	0,                                /*tp_as_buffer*/
+	Py_TPFLAGS_DEFAULT,               /*tp_flags*/
+	RangeDecoder_doc,                 /*tp_doc*/
+	0,                                /*tp_traverse*/
+	0,                                /*tp_clear*/
+	0,                                /*tp_richcompare*/
+	0,                                /*tp_weaklistoffset*/
+	0,                                /*tp_iter*/
+	0,                                /*tp_iternext*/
+	RangeDecoder_methods,             /*tp_methods*/
+	0,                                /*tp_members*/
+	RangeDecoder_getset,              /*tp_getset*/
+	0,                                /*tp_base*/
+	0,                                /*tp_dict*/
+	0,                                /*tp_descr_get*/
+	0,                                /*tp_descr_set*/
+	0,                                /*tp_dictoffset*/
+	(initproc)RangeDecoder_init,      /*tp_init*/
+	0,                                /*tp_alloc*/
+	RangeDecoder_new,                 /*tp_new*/
+};
+
+#if PY_MAJOR_VERSION >= 3
+static PyModuleDef range_coder_module = {
+	PyModuleDef_HEAD_INIT,
+	"_range_coder",
+	"A fast implementation of a range encoder and decoder.",
+	-1, 0, 0, 0, 0, 0
+};
+#endif
+
+
+#if PY_MAJOR_VERSION >= 3
+PyMODINIT_FUNC PyInit__range_coder() {
+	// create module object
+	PyObject* module = PyModule_Create(&range_coder_module);
+#define RETVAL 0;
+#else
+PyMODINIT_FUNC init_range_coder() {
+	PyObject* module = Py_InitModule3(
+		"_range_coder", 0, "A fast implementation of a range encoder and decoder.");
+#define RETVAL void();
+#endif
+
+	if(!module)
+		return RETVAL;
+
+	// initialize types
+	if(PyType_Ready(&RangeEncoder_type) < 0)
+		return RETVAL;
+	if(PyType_Ready(&RangeDecoder_type) < 0)
+		return RETVAL;
+
+	// add types to module
+	Py_INCREF(&RangeEncoder_type);
+	PyModule_AddObject(module, "RangeEncoder", reinterpret_cast<PyObject*>(&RangeEncoder_type));
+	Py_INCREF(&RangeDecoder_type);
+	PyModule_AddObject(module, "RangeDecoder", reinterpret_cast<PyObject*>(&RangeDecoder_type));
+
+#if PY_MAJOR_VERSION >= 3
+	return module;
+#endif
+}