1 files changed, 66 insertions, 0 deletions
diff --git a/gr-digital/python/utils/gray_code.py b/gr-digital/python/utils/gray_code.py
new file mode 100644
index 000000000..926a1ded1
--- /dev/null
+++ b/gr-digital/python/utils/gray_code.py
@@ -0,0 +1,66 @@
+#!/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
+