uint add/sub type checking, fixes #1029

test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py

@@ -52,9 +52,15 @@ class uint(BasicValue, metaclass=BasicType):
         if value < 0:
             raise ValueError("unsigned types must not be negative")
         if cls.byte_len and value.bit_length() > (cls.byte_len << 3):
-            raise ValueError("value out of bounds for uint{}".format(cls.byte_len))
+            raise ValueError("value out of bounds for uint{}".format(cls.byte_len * 8))
         return super().__new__(cls, value)
 
+    def __add__(self, other):
+        return self.__class__(super().__add__(coerce_type_maybe(other, self.__class__, strict=True)))
+
+    def __sub__(self, other):
+        return self.__class__(super().__sub__(coerce_type_maybe(other, self.__class__, strict=True)))
+
     @classmethod
     def default(cls):
         return cls(0)

test_libs/pyspec/eth2spec/utils/ssz/test_ssz_typing.py

@@ -6,6 +6,14 @@ from .ssz_typing import (
 )
 
 
+def expect_value_error(fn, msg):
+    try:
+        fn()
+        raise AssertionError(msg)
+    except ValueError:
+        pass
+
+
 def test_subclasses():
     for u in [uint, uint8, uint16, uint32, uint64, uint128, uint256]:
         assert issubclass(u, uint)
@@ -55,21 +63,13 @@ def test_basic_value_bounds():
         # this should work
         assert k(v - 1) == v - 1
         # but we do not allow overflows
-        try:
-            k(v)
-            assert False
-        except ValueError:
-            pass
+        expect_value_error(lambda: k(v), "no overflows allowed")
 
     for k, _ in max.items():
         # this should work
         assert k(0) == 0
         # but we do not allow underflows
-        try:
-            k(-1)
-            assert False
-        except ValueError:
-            pass
+        expect_value_error(lambda: k(-1), "no underflows allowed")
 
 
 def test_container():
@@ -213,3 +213,15 @@ def test_bytesn_subclass():
     assert not issubclass(Bytes48, Bytes32)
 
     assert len(Bytes32() + Bytes48()) == 80
+
+
+def test_uint_math():
+    assert uint8(0) + uint8(uint32(16)) == uint8(16)  # allow explict casting to make invalid addition valid
+
+    expect_value_error(lambda: uint8(0) - uint8(1), "no underflows allowed")
+    expect_value_error(lambda: uint8(1) + uint8(255), "no overflows allowed")
+    expect_value_error(lambda: uint8(0) + 256, "no overflows allowed")
+    expect_value_error(lambda: uint8(42) + uint32(123), "no mixed types")
+    expect_value_error(lambda: uint32(42) + uint8(123), "no mixed types")
+
+    assert type(uint32(1234) + 56) == uint32