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feat: use 16-bit random value to compute validator indices #7301

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feat: use 16-bit random value to compute validator indices #7301

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65 changes: 38 additions & 27 deletions packages/state-transition/src/util/seed.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ import {
SYNC_COMMITTEE_SIZE,
} from "@lodestar/params";
import {Bytes32, DomainType, Epoch, ValidatorIndex} from "@lodestar/types";
import {assert, bytesToBigInt, intToBytes} from "@lodestar/utils";
import {assert, bytesToBigInt, bytesToInt, intToBytes} from "@lodestar/utils";
import {EffectiveBalanceIncrements} from "../cache/effectiveBalanceIncrements.js";
import {BeaconStateAllForks} from "../types.js";
import {computeStartSlotAtEpoch} from "./epoch.js";
Expand Down Expand Up @@ -57,27 +57,31 @@ export function computeProposerIndex(
throw Error("Validator indices must not be empty");
}

const isPostElectra = fork >= ForkSeq.electra;

// TODO: Inline outside this function
const MAX_RANDOM_BYTE = 2 ** 8 - 1;
const MAX_EFFECTIVE_BALANCE_INCREMENT =
fork >= ForkSeq.electra
? MAX_EFFECTIVE_BALANCE_ELECTRA / EFFECTIVE_BALANCE_INCREMENT
: MAX_EFFECTIVE_BALANCE / EFFECTIVE_BALANCE_INCREMENT;
const MAX_RANDOM_VALUE = isPostElectra ? 2 ** 16 - 1 : 2 ** 8 - 1;
const MAX_EFFECTIVE_BALANCE_INCREMENT = isPostElectra
? MAX_EFFECTIVE_BALANCE_ELECTRA / EFFECTIVE_BALANCE_INCREMENT
: MAX_EFFECTIVE_BALANCE / EFFECTIVE_BALANCE_INCREMENT;

let i = 0;
/* eslint-disable-next-line no-constant-condition */
while (true) {
const candidateIndex = indices[computeShuffledIndex(i % indices.length, indices.length, seed)];
const randByte = digest(
Buffer.concat([
seed,
//
intToBytes(Math.floor(i / 32), 8, "le"),
])
)[i % 32];

let randValue: number;

if (isPostElectra) {
const randByte = digest(Buffer.concat([seed, intToBytes(Math.floor(i / 16), 8, "le")]));
const offset = (i % 16) * 2;
randValue = bytesToInt(randByte.subarray(offset, offset + 2));
} else {
randValue = digest(Buffer.concat([seed, intToBytes(Math.floor(i / 32), 8, "le")]))[i % 32];
}

const effectiveBalanceIncrement = effectiveBalanceIncrements[candidateIndex];
if (effectiveBalanceIncrement * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE_INCREMENT * randByte) {
if (effectiveBalanceIncrement * MAX_RANDOM_VALUE >= MAX_EFFECTIVE_BALANCE_INCREMENT * randValue) {
return candidateIndex;
}
i += 1;
Expand All @@ -100,12 +104,12 @@ export function getNextSyncCommitteeIndices(
activeValidatorIndices: ArrayLike<ValidatorIndex>,
effectiveBalanceIncrements: EffectiveBalanceIncrements
): ValidatorIndex[] {
const isPostElectra = fork >= ForkSeq.electra;
// TODO: Bechmark if it's necessary to inline outside of this function
const MAX_RANDOM_BYTE = 2 ** 8 - 1;
const MAX_EFFECTIVE_BALANCE_INCREMENT =
fork >= ForkSeq.electra
? MAX_EFFECTIVE_BALANCE_ELECTRA / EFFECTIVE_BALANCE_INCREMENT
: MAX_EFFECTIVE_BALANCE / EFFECTIVE_BALANCE_INCREMENT;
const MAX_RANDOM_BYTE = isPostElectra ? 2 ** 16 - 1 : 2 ** 8 - 1;
const MAX_EFFECTIVE_BALANCE_INCREMENT = isPostElectra
? MAX_EFFECTIVE_BALANCE_ELECTRA / EFFECTIVE_BALANCE_INCREMENT
: MAX_EFFECTIVE_BALANCE / EFFECTIVE_BALANCE_INCREMENT;

const epoch = computeEpochAtSlot(state.slot) + 1;

Expand All @@ -116,16 +120,23 @@ export function getNextSyncCommitteeIndices(
while (syncCommitteeIndices.length < SYNC_COMMITTEE_SIZE) {
const shuffledIndex = computeShuffledIndex(i % activeValidatorCount, activeValidatorCount, seed);
const candidateIndex = activeValidatorIndices[shuffledIndex];
const randByte = digest(
Buffer.concat([
seed,
//
intToBytes(Math.floor(i / 32), 8, "le"),
])
)[i % 32];
let randValue: number;
if (isPostElectra) {
const randByte = digest(Buffer.concat([seed, intToBytes(Math.floor(i / 16), 8, "le")]));
const offset = (i % 16) * 2;
randValue = bytesToInt(randByte.subarray(offset, offset + 2));
} else {
randValue = digest(
Buffer.concat([
seed,
//
intToBytes(Math.floor(i / 32), 8, "le"),
])
)[i % 32];
}

const effectiveBalanceIncrement = effectiveBalanceIncrements[candidateIndex];
if (effectiveBalanceIncrement * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE_INCREMENT * randByte) {
if (effectiveBalanceIncrement * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE_INCREMENT * randValue) {
syncCommitteeIndices.push(candidateIndex);
}

Expand Down
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