Create uplink.py (#55)

First basic functionality for uplink messages - UF and ICAO address.

pyModeS/decoder/uplink.py

@@ -0,0 +1,24 @@
+from pyModeS.decoder import common
+
+def uplink_icao(msg):
+	"""Calculate the ICAO address from a Mode-S interrogation (uplink message)"""
+	p_gen = 0xfffa0480 << ((len(msg)-14)*4)
+	data = int(msg[:-6],16)
+	PA = int(msg[-6:],16)
+	ad = 0
+	topbit = 0b1 << (len(msg)*4-25)
+	for j in range(0,len(msg)*4,1):
+		if (data & topbit):
+			data^=p_gen
+		data = (data << 1) + ((PA >> 23) & 1)
+		PA = PA << 1
+		if (j>(len(msg)*4-26)):
+			ad = ad + ((data >> (len(msg)*4-25)) & 1)
+			ad = ad << 1
+	return "%06X" % (ad >> 2)
+
+
+def uf(msg):
+    """Decode Uplink Format value, bits 1 to 5."""
+    ufbin = common.hex2bin(msg[:2])
+    return min(common.bin2int(ufbin[0:5]), 24)