Use sympy for faster factorization if available (#199)

README.rst

@@ -127,6 +127,11 @@ There you'll find a list of all the methods, types and available constructors.
 
 More examples are also available under the ``telethon_examples/`` folder.
 
+If you're using Telethon under ARM, you may want to install ``sympy`` through
+``pip`` for a substantial speed-up when generating the keys required to
+connect to Telegram (you can of course do this on desktop too). See
+`issue #199 <https://github.com/LonamiWebs/Telethon/issues/199>`_ for more.
+
 Common errors
 -------------
 

telethon/crypto/factorization.py

@@ -1,4 +1,8 @@
 from random import randint
+try:
+    import sympy.ntheory
+except ImportError:
+    sympy = None
 
 
 class Factorization:
@@ -58,5 +62,8 @@ class Factorization:
     @staticmethod
     def factorize(pq):
         """Factorizes the given number and returns both the divisor and the number divided by the divisor"""
+        if sympy:
+            return tuple(sympy.ntheory.factorint(pq).keys())
+        else:
             divisor = Factorization.find_small_multiplier_lopatin(pq)
             return divisor, pq // divisor