prysm-pulse/beacon-chain/state/stateutil/participation_bit_root.go

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package stateutil
import (
"encoding/binary"
"github.com/pkg/errors"
fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
"github.com/prysmaticlabs/prysm/crypto/hash"
"github.com/prysmaticlabs/prysm/encoding/ssz"
)
// ParticipationBitsRoot computes the HashTreeRoot merkleization of
// participation roots.
func ParticipationBitsRoot(bits []byte) ([32]byte, error) {
hasher := hash.CustomSHA256Hasher()
chunkedRoots, err := packParticipationBits(bits)
if err != nil {
return [32]byte{}, err
}
limit := (uint64(fieldparams.ValidatorRegistryLimit + 31)) / 32
bytesRoot, err := ssz.BitwiseMerkleize(hasher, chunkedRoots, uint64(len(chunkedRoots)), limit)
if err != nil {
return [32]byte{}, errors.Wrap(err, "could not compute merkleization")
}
bytesRootBufRoot := make([]byte, 32)
binary.LittleEndian.PutUint64(bytesRootBufRoot[:8], uint64(len(bits)))
return ssz.MixInLength(bytesRoot, bytesRootBufRoot), nil
}
// packParticipationBits into chunks. It'll pad the last chunk with zero bytes if
// it does not have length bytes per chunk.
func packParticipationBits(bytes []byte) ([][32]byte, error) {
numItems := len(bytes)
chunks := make([][32]byte, 0, numItems/32)
for i := 0; i < numItems; i += 32 {
j := i + 32
// We create our upper bound index of the chunk, if it is greater than numItems,
// we set it as numItems itself.
if j > numItems {
j = numItems
}
// We create chunks from the list of items based on the
// indices determined above.
chunk := [32]byte{}
copy(chunk[:], bytes[i:j])
chunks = append(chunks, chunk)
}
if len(chunks) == 0 {
return chunks, nil
}
return chunks, nil
}