Use 16-bit random value in validator filter

[jtraglia]

PR Description

This PR implements the changes defined here:

• Use 16-bit random value in validator filter ethereum/consensus-specs#4039

Notably, this PR will:

• Override computeProposerIndex and getNextSyncCommitteeIndices.
• In computeProposerIndex, rename hash to randomBytes to match the spec.
• Add cached randomBytes to getNextSyncCommitteeIndices.
• Define new MAX_RANDOM_VALUE equal to 2**16-1.

See the original implementations here:

teku/ethereum/spec/src/main/java/tech/pegasys/teku/spec/logic/common/helpers/MiscHelpers.java

Lines 112 to 139 in 7de9aa4

	protected int computeProposerIndex(
	final BeaconState state,
	final IntList indices,
	final Bytes32 seed,
	final UInt64 maxEffectiveBalance) {
	checkArgument(!indices.isEmpty(), "compute_proposer_index indices must not be empty");
	final Sha256 sha256 = getSha256Instance();
	int i = 0;
	final int total = indices.size();
	byte[] hash = null;
	while (true) {
	final int candidateIndex = indices.getInt(computeShuffledIndex(i % total, total, seed));
	if (i % 32 == 0) {
	hash = sha256.digest(seed, uint64ToBytes(Math.floorDiv(i, 32L)));
	}
	final int randomByte = UnsignedBytes.toInt(hash[i % 32]);
	final UInt64 validatorEffectiveBalance =
	state.getValidators().get(candidateIndex).getEffectiveBalance();
	if (validatorEffectiveBalance
	.times(MAX_RANDOM_BYTE)
	.isGreaterThanOrEqualTo(maxEffectiveBalance.times(randomByte))) {
	return candidateIndex;
	}
	i++;
	}
	}

teku/ethereum/spec/src/main/java/tech/pegasys/teku/spec/logic/versions/altair/helpers/BeaconStateAccessorsAltair.java

Lines 104 to 132 in 7de9aa4

	protected IntList getNextSyncCommitteeIndices(
	final BeaconState state, final UInt64 maxEffectiveBalance) {
	final UInt64 epoch = getCurrentEpoch(state).plus(1);
	final IntList activeValidatorIndices = getActiveValidatorIndices(state, epoch);
	final int activeValidatorCount = activeValidatorIndices.size();
	checkArgument(activeValidatorCount > 0, "Provided state has no active validators");
	final Bytes32 seed = getSeed(state, epoch, Domain.SYNC_COMMITTEE);
	int i = 0;
	final SszList<Validator> validators = state.getValidators();
	final IntList syncCommitteeIndices = new IntArrayList();
	final int syncCommitteeSize = altairConfig.getSyncCommitteeSize();
	final Sha256 sha256 = getSha256Instance();
	while (syncCommitteeIndices.size() < syncCommitteeSize) {
	final int shuffledIndex =
	miscHelpers.computeShuffledIndex(i % activeValidatorCount, activeValidatorCount, seed);
	final int candidateIndex = activeValidatorIndices.getInt(shuffledIndex);
	final int randomByte =
	ByteUtil.toUnsignedInt(sha256.digest(seed, uint64ToBytes(i / 32))[i % 32]);
	final UInt64 effectiveBalance = validators.get(candidateIndex).getEffectiveBalance();
	if (effectiveBalance
	.times(MAX_RANDOM_BYTE)
	.isGreaterThanOrEqualTo(maxEffectiveBalance.times(randomByte))) {
	syncCommitteeIndices.add(candidateIndex);
	}
	i++;
	}

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[tbenr]

in this PR we should re-enable2 fizzing tests disabled here: #8923

[jtraglia]

Hmm I'm not sure why these are still failing. The only difference is the body_root.

[rolfyone]

Hmm I'm not sure why these are still failing. The only difference is the body_root.

I've got a body root diff in mine too...

[tbenr]

this is weird. I'll spend some more time on it tomorrow, if in the meantime you don't solve the mystery

[tbenr]

lol, my bad. Seems like I copied the wrong spec files. I also fixed a uint test that seems to be affected by the change

[jtraglia]

Haha no worries. Thank you for fixing this. Comparing prettySerialize outputs is a good idea too!

[tbenr]

LGTM