Move shufflings code together into seed util (#3710)

packages/beacon-state-transition/src/allForks/util/epochContext.ts

@@ -1,4 +1,4 @@
-import {ByteVector, hash, BitList, List, readonlyValuesListOfLeafNodeStruct} from "@chainsafe/ssz";
+import {ByteVector, BitList, List, readonlyValuesListOfLeafNodeStruct} from "@chainsafe/ssz";
 import bls, {CoordType, PublicKey} from "@chainsafe/bls";
 import {
   BLSSignature,
@@ -14,7 +14,6 @@ import {
 import {IBeaconConfig} from "@chainsafe/lodestar-config";
 import {
   BASE_REWARD_FACTOR,
-  DOMAIN_BEACON_PROPOSER,
   EFFECTIVE_BALANCE_INCREMENT,
   FAR_FUTURE_EPOCH,
   GENESIS_EPOCH,
@@ -24,16 +23,15 @@ import {
   SYNC_REWARD_WEIGHT,
   WEIGHT_DENOMINATOR,
 } from "@chainsafe/lodestar-params";
-import {bigIntSqrt, intToBytes, LodestarError} from "@chainsafe/lodestar-utils";
+import {bigIntSqrt, LodestarError} from "@chainsafe/lodestar-utils";
 import {MutableVector} from "@chainsafe/persistent-ts";
 
 import {
   computeActivationExitEpoch,
   computeEpochAtSlot,
-  computeProposerIndex,
+  computeProposers,
   computeStartSlotAtEpoch,
   getChurnLimit,
-  getSeed,
   isActiveValidator,
   isAggregatorFromCommitteeLength,
   zipIndexesCommitteeBits,
@@ -269,29 +267,6 @@ export function syncPubkeys(
   }
 }
 
-/**
- * Compute proposer indices for an epoch
- */
-export function computeProposers(
-  state: allForks.BeaconState,
-  shuffling: IEpochShuffling,
-  effectiveBalances: MutableVector<number>
-): number[] {
-  const epochSeed = getSeed(state, shuffling.epoch, DOMAIN_BEACON_PROPOSER);
-  const startSlot = computeStartSlotAtEpoch(shuffling.epoch);
-  const proposers = [];
-  for (let slot = startSlot; slot < startSlot + SLOTS_PER_EPOCH; slot++) {
-    proposers.push(
-      computeProposerIndex(
-        effectiveBalances,
-        shuffling.activeIndices,
-        hash(Buffer.concat([epochSeed, intToBytes(slot, 8)]))
-      )
-    );
-  }
-  return proposers;
-}
-
 /**
  * Same logic in https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.5/specs/altair/beacon-chain.md#sync-committee-processing
  */

packages/beacon-state-transition/src/util/index.ts

@@ -12,7 +12,6 @@ export * from "./domain";
 export * from "./epoch";
 export * from "./genesis";
 export * from "./interop";
-export * from "./proposer";
 export * from "./seed";
 export * from "./shuffle";
 export * from "./shufflingDecisionRoot";

packages/beacon-state-transition/src/util/seed.ts

@@ -3,9 +3,81 @@
  */
 
 import {hash} from "@chainsafe/ssz";
-import {Epoch, Bytes32, DomainType, allForks} from "@chainsafe/lodestar-types";
+import {Epoch, Bytes32, DomainType, allForks, ValidatorIndex} from "@chainsafe/lodestar-types";
 import {assert, bytesToBigInt, intToBytes} from "@chainsafe/lodestar-utils";
-import {EPOCHS_PER_HISTORICAL_VECTOR, MIN_SEED_LOOKAHEAD, SHUFFLE_ROUND_COUNT} from "@chainsafe/lodestar-params";
+import {
+  DOMAIN_BEACON_PROPOSER,
+  EPOCHS_PER_HISTORICAL_VECTOR,
+  MAX_EFFECTIVE_BALANCE,
+  MIN_SEED_LOOKAHEAD,
+  SHUFFLE_ROUND_COUNT,
+  SLOTS_PER_EPOCH,
+} from "@chainsafe/lodestar-params";
+import {IEpochShuffling} from "../allForks";
+import {MutableVector} from "@chainsafe/persistent-ts";
+import {computeStartSlotAtEpoch} from "./epoch";
+
+/**
+ * Compute proposer indices for an epoch
+ */
+export function computeProposers(
+  state: allForks.BeaconState,
+  shuffling: IEpochShuffling,
+  effectiveBalances: MutableVector<number>
+): number[] {
+  const epochSeed = getSeed(state, shuffling.epoch, DOMAIN_BEACON_PROPOSER);
+  const startSlot = computeStartSlotAtEpoch(shuffling.epoch);
+  const proposers = [];
+  for (let slot = startSlot; slot < startSlot + SLOTS_PER_EPOCH; slot++) {
+    proposers.push(
+      computeProposerIndex(
+        effectiveBalances,
+        shuffling.activeIndices,
+        hash(Buffer.concat([epochSeed, intToBytes(slot, 8)]))
+      )
+    );
+  }
+  return proposers;
+}
+
+/**
+ * Return from ``indices`` a random index sampled by effective balance.
+ *
+ * SLOW CODE - 🐢
+ */
+export function computeProposerIndex(
+  effectiveBalances: MutableVector<number>,
+  indices: ValidatorIndex[],
+  seed: Uint8Array
+): ValidatorIndex {
+  assert.gt(indices.length, 0, "Validator indices must not be empty");
+
+  // TODO: Inline outside this function
+  const MAX_RANDOM_BYTE = 2 ** 8 - 1;
+
+  let i = 0;
+  /* eslint-disable-next-line no-constant-condition */
+  while (true) {
+    const candidateIndex = indices[computeShuffledIndex(i % indices.length, indices.length, seed)];
+    const randByte = hash(
+      Buffer.concat([
+        seed,
+        //
+        intToBytes(Math.floor(i / 32), 8),
+      ])
+    )[i % 32];
+
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const effectiveBalance = effectiveBalances.get(candidateIndex)!;
+    if (effectiveBalance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE * randByte) {
+      return candidateIndex;
+    }
+    i += 1;
+    if (i === indices.length) {
+      return -1;
+    }
+  }
+}
 
 /**
  * Return the shuffled validator index corresponding to ``seed`` (and ``index_count``).

packages/beacon-state-transition/test/perf/allForks/util/shufflings.test.ts

@@ -1,9 +1,10 @@
 import {itBench} from "@dapplion/benchmark";
 import {Epoch} from "@chainsafe/lodestar-types";
 import {computeEpochAtSlot, CachedBeaconStateAllForks} from "../../../../src";
-import {computeEpochShuffling, computeProposers} from "../../../../src/allForks";
+import {computeEpochShuffling} from "../../../../src/allForks";
 import {generatePerfTestCachedStatePhase0, numValidators} from "../../util";
 import {getNextSyncCommittee} from "../../../../src/altair/util/syncCommittee";
+import {computeProposers} from "../../../../src/util/seed";
 
 describe("epoch shufflings", () => {
   let state: CachedBeaconStateAllForks;