fix issue 12

Author: hiroaki.kawai

src/geohash.cpp

@@ -103,7 +103,7 @@ static inline int double_to_i64(double in, uint64_t *out){
 	if(shift > 0){
 		x.i64 <<= shift;
 	}else{
-		x.i64 >>= shift;
+		x.i64 >>= -shift;
 	}
 	if(sign){
 		x.i64 =  UINT64_C(0x8000000000000000) - x.i64;

test/test_geohash.py

@@ -58,6 +58,11 @@ def test_ezs42(self):
 		x=geohash.bbox('ezs42')
 		self.assertEqual(round(x['s'],3), 42.583)
 		self.assertEqual(round(x['n'],3), 42.627)
+	
+	def test_issue12(self):
+		ll=geohash.decode(geohash.encode(51.566141,-0.009434,24))
+		self.assertAlmostEqual(ll[0], 51.566141)
+		self.assertAlmostEqual(ll[1], -0.009434)
 
 class TestNeighbors(unittest.TestCase):
 	def test_empty(self):