status-im
/
eth2.0-specs
mirror of https://github.com/status-im/eth2.0-specs.git
2
0
Fork 0
Code Issues Projects Releases Wiki Activity

SSZ list Merkle hashing change 

The current spec is arguably inconsistent, in that if a set of N values gets chunked into M chunks where M is not an exact power of 2, the chunks between M and next_power_of_2(M) are filled with SSZ_CHUNK_SIZE zero bytes each, but the last chunk is not padded, and could be arbitrarily short (eg. if the values are 4 bytes and there are 257 of them, then that gets serialized into eight chunks chunks where the first four are 64 values each, the fifth is 4 bytes corresponding to the last value, and the last three chunks are SSZ_CHUNK_SIZE zero bytes). This PR fills every chunk up to exactly SSZ_CHUNK_SIZE bytes for consistency.
This commit is contained in:
vbuterin 2019-01-31 10:12:43 -06:00 committed by GitHub
parent 4cdb66728a
commit 5488e7b6a4
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 2 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
specs/simple-serialize.md
View File

@ -385,7 +385,7 @@ Return the hash of the serialization of the value.
#### List/Vectors
First, we define some helpers and then the Merkle tree function.
First, we define some helpers and then the Merkle tree function. `zpad(input: bytes, length: int) -> bytes` is a helper that extends the given `bytes` value to the desired `length` by adding zero bytes on the right.
```python
# Merkle tree hash of a list of homogenous, non-empty items
@ -401,7 +401,7 @@ def merkle_hash(lst):
items_per_chunk = SSZ_CHUNK_SIZE // len(lst[0])
# Build a list of chunks based on the number of items in the chunk
chunkz = [b''.join(lst[i:i+items_per_chunk]) for i in range(0, len(lst), items_per_chunk)]
chunkz = [zpad(b''.join(lst[i:i+items_per_chunk]), SSZ_CHUNK_SIZE) for i in range(0, len(lst), items_per_chunk)]
else:
# Leave large items alone
chunkz = lst