From 818207a4d859a5e040cdfcb99a3fcf3716ac2df9 Mon Sep 17 00:00:00 2001
From: Junzi Sun <junzi.sun@gmail.com>
Date: Thu, 28 Jan 2016 11:14:14 +0100
Subject: [PATCH] simplify hex2bin()

---
 decoder.py | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/decoder.py b/decoder.py
index f025167..9485106 100644
--- a/decoder.py
+++ b/decoder.py
@@ -42,11 +42,10 @@ MODES_CHECKSUM_TABLE = [
 
 def hex2bin(hexstr):
     """Convert a hexdecimal string to binary string, with zero fillings. """
-    length = len(hexstr) * 4
-    msgbin = bin(int(hexstr, 16))[2:]
-    while ((len(msgbin)) < length):
-        msgbin = '0' + msgbin
-    return msgbin
+    scale = 16
+    num_of_bits = len(hexstr) * math.log(scale, 2)
+    binstr = bin(int(hexstr, scale))[2:].zfill(int(num_of_bits))
+    return binstr
 
 
 def bin2int(binstr):
@@ -230,6 +229,7 @@ def cpr2position(cprlat0, cprlat1, cprlon0, cprlon1, t0, t1):
 
     return lat, lon
 
+
 def get_velocity(msg):
     """Calculate the speed, heading, and vertical rate"""