From 55f5f106f175d64d48befc910025f1f9c33b39c1 Mon Sep 17 00:00:00 2001 From: vbuterin Date: Thu, 1 Aug 2019 10:56:31 -0400 Subject: [PATCH] Updated type checkers for generalized index functions. --- specs/light_client/merkle_proofs.md | 44 +++++++++++++---------------- 1 file changed, 20 insertions(+), 24 deletions(-) diff --git a/specs/light_client/merkle_proofs.md b/specs/light_client/merkle_proofs.md index dae2a1704..6107e459c 100644 --- a/specs/light_client/merkle_proofs.md +++ b/specs/light_client/merkle_proofs.md @@ -17,12 +17,6 @@ -## Constants - -| Name | Value | -| - | - | -| `LENGTH_FLAG` | `2**64 - 1` | - ## Generalized Merkle tree index In a binary Merkle tree, we define a "generalized index" of a node as `2**depth + index`. Visually, this looks as follows: @@ -38,7 +32,8 @@ Note that the generalized index has the convenient property that the two childre ```python def merkle_tree(leaves: List[Bytes32]) -> List[Bytes32]: - o = [0] * len(leaves) + leaves + padded_length = next_power_of_2(len(leaves)) + o = [ZERO_HASH] * padded_length + leaves + [ZERO_HASH] * (padded_length - len(leaves)) for i in range(len(leaves) - 1, 0, -1): o[i] = hash(o[i * 2] + o[i * 2 + 1]) return o @@ -64,27 +59,24 @@ y_data_root len(y) We can now define a concept of a "path", a way of describing a function that takes as input an SSZ object and outputs some specific (possibly deeply nested) member. For example, `foo -> foo.x` is a path, as are `foo -> len(foo.y)` and `foo -> foo.y[5].w`. We'll describe paths as lists, which can have two representations. In "human-readable form", they are `["x"]`, `["y", "__len__"]` and `["y", 5, "w"]` respectively. In "encoded form", they are lists of `uint64` values, in these cases (assuming the fields of `foo` in order are `x` then `y`, and `w` is the first field of `y[i]`) `[0]`, `[1, 2**64-1]`, `[1, 5, 0]`. ```python -def item_length(typ: Type) -> int: +def item_length(typ: SSZType) -> int: """ Returns the number of bytes in a basic type, or 32 (a full hash) for compound types. """ - if typ == bool: - return 1 - elif issubclass(typ, uint): + if issubclass(typ, BasicValue): return typ.byte_len else: return 32 -def get_elem_type(typ: Type, index: int) -> Type: +def get_elem_type(typ: ComplexType, index: int) -> Type: """ Returns the type of the element of an object of the given type with the given index or member variable name (eg. `7` for `x[7]`, `"foo"` for `x.foo`) """ - return typ.get_fields_dict()[index] if is_container_type(typ) else typ.elem_type + return typ.get_fields()[key] if issubclass(typ, Container) else typ.elem_type - -def get_chunk_count(typ: Type) -> int: +def chunk_count(typ: SSZType) -> int: """ Returns the number of hashes needed to represent the top-level elements in the given type (eg. `x.foo` or `x[7]` but not `x[7].bar` or `x.foo.baz`). In all cases except lists/vectors @@ -92,24 +84,28 @@ def get_chunk_count(typ: Type) -> int: hash. For lists/vectors of basic types, it is often fewer because multiple basic elements can be packed into one 32-byte chunk. """ - if is_basic_type(typ): + if issubclass(typ, BasicValue): return 1 - elif issubclass(typ, (List, Vector, Bytes, BytesN)): + elif issubclass(typ, Bits): + return (typ.length + 255) // 256 + elif issubclass(typ, Elements): return (typ.length * item_length(typ.elem_type) + 31) // 32 - else: + elif issubclass(typ, Container): return len(typ.get_fields()) + else: + raise Exception(f"Type not supported: {typ}") -def get_item_position(typ: Type, index: Union[int, str]) -> Tuple[int, int, int]: +def get_item_position(typ: SSZType, index: Union[int, str]) -> Tuple[int, int, int]: """ Returns three variables: (i) the index of the chunk in which the given element of the item is represented, (ii) the starting byte position, (iii) the ending byte position. For example for a 6-item list of uint64 values, index=2 will return (0, 16, 24), index=5 will return (1, 8, 16) """ - if issubclass(typ, (List, Vector, Bytes, BytesN)): + if issubclass(typ, Elements): start = index * item_length(typ.elem_type) return start // 32, start % 32, start % 32 + item_length(typ.elem_type) - elif is_container_type(typ): + elif issubclass(typ, Container): return typ.get_field_names().index(index), 0, item_length(get_elem_type(typ, index)) else: raise Exception("Only lists/vectors/containers supported") @@ -122,12 +118,12 @@ def get_generalized_index(typ: Type, path: List[Union[int, str]]) -> Generalized """ root = 1 for p in path: - assert not is_basic_type(typ) # If we descend to a basic type, the path cannot continue further + assert not issubclass(typ, BasicValue) # If we descend to a basic type, the path cannot continue further if p == '__len__': typ, root = uint256, root * 2 + 1 if issubclass(typ, (List, Bytes)) else None else: pos, _, _ = get_item_position(typ, p) - root = root * (2 if issubclass(typ, (List, Bytes)) else 1) * next_power_of_two(get_chunk_count(typ)) + pos + root = root * (2 if issubclass(typ, (List, Bytes)) else 1) * next_power_of_two(chunk_count(typ)) + pos typ = get_elem_type(typ, p) return root ``` @@ -197,7 +193,7 @@ def get_branch_indices(tree_index: int) -> List[int]: def get_expanded_indices(indices: List[int]) -> List[int]: """ Get the generalized indices of all chunks in the tree needed to prove the chunks with the given - generalized indices. + generalized indices, including the leaves. """ branches = set() for index in indices: