fix int type encoding in abi

Author: Jan Xie

ethereum/abi.py

@@ -149,7 +149,7 @@ class ValueOutOfBounds(EncodingError):
 def decint(n):
     if isinstance(n, str):
         n = utils.to_string(n)
-    if is_numeric(n) and n < 2**256 and n > -2**255:
+    if is_numeric(n) and n < 2**256 and n >= -2**255:
         return n
     elif is_numeric(n):
         raise EncodingError("Number out of range: %r" % n)

ethereum/tests/test_abi.py

@@ -18,6 +18,8 @@ def test_abi_encode_signed_int():
     assert abi.decode_abi(['int8'], abi.encode_abi(['int8'], [-1]))[0] == -1
 
 def test_abi_encode_single_int():
+    assert abi.encode_single(['int', '256', []], -2**255) == (b'\x80'+b'\x00'*31)
+
     assert abi.encode_single(['int', '8', []], -128) == zpad(b'\x80', 32)
     with pytest.raises(abi.ValueOutOfBounds):
         assert abi.encode_single(['int', '8', []], -129)