fix #12, fixed rounding error, code refactor

aprslib/base91.py

@@ -20,10 +20,16 @@ Provides facilities for covertion from/to base91
 """
 
 __all__ = ['to_decimal', 'from_decimal']
-from math import log
+from math import log, ceil
+import sys
 from re import findall
 from . import string_type, int_type
 
+if sys.version_info < (3,):
+    _range = xrange
+else:
+    _range = range
+
 
 def to_decimal(text):
     """
@@ -36,6 +42,7 @@ def to_decimal(text):
     if findall(r"[\x00-\x20\x7c-\xff]", text):
         raise ValueError("invalid character in sequence")
 
+    text = text.lstrip('!')
     decimal = 0
     length = len(text) - 1
     for i, char in enumerate(text):
@@ -60,12 +67,15 @@ def from_decimal(number, padding=1):
     elif padding < 1:
         raise ValueError("Expected padding to be >0")
     elif number > 0:
-        for divisor in [91**e for e in reversed(range(int(log(number) / log(91)) + 1))]:
-            quotient = number // divisor
-            number = number % divisor
+        max_n = ceil(log(number) / log(91))
+
+        for n in _range(int(max_n), -1, -1):
+            quotient, number = divmod(number, 91**n)
             text.append(chr(33 + quotient))
 
-    # add padding if necessary
-    text = ['!'] * (padding-len(text)) + text
+    text = "".join(text).lstrip('!')
 
-    return "".join(text)
+    # add padding if necessary
+    text = '!' * (padding-len(text)) + text
+
+    return text

setup.py

@@ -24,7 +24,9 @@ setup(
         'Intended Audience :: Developers',
         'License :: OSI Approved :: GNU General Public License v2 (GPLv2)',
         'Programming Language :: Python',
-        'Programming Language :: Python :: 2.7',
+        'Programming Language :: Python :: 2',
+        'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: Implementation :: PyPy',
         'Topic :: Communications :: Ham Radio',
     ],
     test_suite='tests',

tests/test_base91.py

@@ -104,7 +104,7 @@ class c_Both(unittest.TestCase):
             self.assertEqual(result, number)
 
     def test_stability(self):
-        for number in range(50):
+        for number in range(200):
             largeN = 91 ** number
             text = base91.from_decimal(largeN)
             result = base91.to_decimal(text)