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#!/usr/bin/env python
#
# Copyright 2011 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# GNU Radio is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3, or (at your option)
# any later version.
#
# GNU Radio is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING. If not, write to
# the Free Software Foundation, Inc., 51 Franklin Street,
# Boston, MA 02110-1301, USA.
#
class GrayCodeGenerator(object):
"""
Generates and caches gray codes.
"""
def __init__(self):
self.gcs = [0, 1]
# The last power of two passed through.
self.lp2 = 2
# The next power of two that will be passed through.
self.np2 = 4
# Curent index
self.i = 2
def get_gray_code(self, length):
"""
Returns a list of gray code of given length.
"""
if len(self.gcs) < length:
self.generate_new_gray_code(length)
return self.gcs[:length]
def generate_new_gray_code(self, length):
"""
Generates new gray code and places into cache.
"""
while len(self.gcs) < length:
if self.i == self.lp2:
# if i is a power of two then gray number is of form 1100000...
result = self.i + self.i/2
else:
# if not we take advantage of the symmetry of all but the last bit
# around a power of two.
result = self.gcs[2*self.lp2-1-self.i] + self.lp2
self.gcs.append(result)
self.i += 1
if self.i == self.np2:
self.lp2 = self.i
self.np2 = self.i*2
_gray_code_generator = GrayCodeGenerator()
gray_code = _gray_code_generator.get_gray_code
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