From a5154da1ff76e8b768e64987471820f958c391d1 Mon Sep 17 00:00:00 2001
From: protolambda <proto@protolambda.com>
Date: Thu, 27 Jun 2019 15:40:40 +0200
Subject: [PATCH] suggestion to implement bitfield like

---
 .../pyspec/eth2spec/utils/ssz/ssz_impl.py     |  4 ++-
 .../pyspec/eth2spec/utils/ssz/ssz_typing.py   | 33 ++++++++++++++-----
 2 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/test_libs/pyspec/eth2spec/utils/ssz/ssz_impl.py b/test_libs/pyspec/eth2spec/utils/ssz/ssz_impl.py
index 7298fb3ca..f0ee944bd 100644
--- a/test_libs/pyspec/eth2spec/utils/ssz/ssz_impl.py
+++ b/test_libs/pyspec/eth2spec/utils/ssz/ssz_impl.py
@@ -1,7 +1,7 @@
 from ..merkle_minimal import merkleize_chunks
 from ..hash_function import hash
 from .ssz_typing import (
-    SSZValue, SSZType, BasicValue, BasicType, Series, Elements, boolean, Container, List, Bytes,
+    SSZValue, SSZType, BasicValue, BasicType, Series, Elements, Bitfield, boolean, Container, List, Bytes,
     Bitlist, Bitvector, uint,
 )
 
@@ -128,6 +128,8 @@ def item_length(typ: SSZType) -> int:
 def chunk_count(typ: SSZType) -> int:
     if isinstance(typ, BasicType):
         return 1
+    elif issubclass(typ, Bitfield):
+        return (typ.length + 7) // 8 // 32
     elif issubclass(typ, Elements):
         return (typ.length * item_length(typ.elem_type) + 31) // 32
     elif issubclass(typ, Container):
diff --git a/test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py b/test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py
index 6ce2b1538..53ab42743 100644
--- a/test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py
+++ b/test_libs/pyspec/eth2spec/utils/ssz/ssz_typing.py
@@ -281,10 +281,6 @@ class ElementsType(ParamsMeta):
     length: int
 
 
-class BitElementsType(ElementsType):
-    elem_type = boolean
-
-
 class Elements(ParamsBase, metaclass=ElementsType):
     pass
 
@@ -346,11 +342,16 @@ class BaseList(list, Elements):
         return self[len(self) - 1]
 
 
-class BaseBitfield(BaseList, metaclass=BitElementsType):
-    elem_type = bool
+class BitElementsType(ElementsType):
+    elem_type: SSZType = boolean
+    length: int
 
 
-class Bitlist(BaseBitfield):
+class Bitfield(BaseList, metaclass=BitElementsType):
+    pass
+
+
+class Bitlist(Bitfield):
     @classmethod
     def is_fixed_size(cls):
         return False
@@ -360,15 +361,29 @@ class Bitlist(BaseBitfield):
         return cls()
 
 
-class Bitvector(BaseBitfield):
+class Bitvector(Bitfield):
+
+    @classmethod
+    def extract_args(cls, *args):
+        if len(args) == 0:
+            return cls.default()
+        else:
+            return super().extract_args(*args)
+
+    @classmethod
+    def value_check(cls, value):
+        # check length limit strictly
+        return len(value) == cls.length and super().value_check(value)
+
     @classmethod
     def is_fixed_size(cls):
         return True
-    
+
     @classmethod
     def default(cls):
         return cls(0 for _ in range(cls.length))
 
+
 class List(BaseList):
 
     @classmethod