chore: give reasoning on how UintNum64 is good for state.slashings

ChainSafe · Nov 24, 2023 · ac08e7d · dapplion · Nov 28, 2023 · ac08e7d
1 parent 0df2f64
commit ac08e7d
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Showing 2 changed files with 13 additions and 3 deletions.
diff --git a/packages/state-transition/src/block/slashValidator.ts b/packages/state-transition/src/block/slashValidator.ts
@@ -37,9 +37,12 @@ export function slashValidator(
   validator.withdrawableEpoch = Math.max(validator.withdrawableEpoch, epoch + EPOCHS_PER_SLASHINGS_VECTOR);
 
   const {effectiveBalance} = validator;
-  // state.slashings is a number because it's reset per epoch in processSlashingsReset()
-  // for each epoch, there are 8704 max validators to slash so it's safe to use Number
-  // also we don't need to compute the total slashings from state.slashings, it's handled by totalSlashingsByIncrement in EpochCache
+
+  // state.slashings is initially a Gwei (BigInt) vector, however since Nov 2023 it's converted to UintNum64 (number) vector in the state transition because:
+  //  - state.slashings[nextEpoch % EPOCHS_PER_SLASHINGS_VECTOR] is reset per epoch in processSlashingsReset()
+  //  - max slashed validators per epoch is SLOTS_PER_EPOCH * MAX_ATTESTER_SLASHINGS * MAX_VALIDATORS_PER_COMMITTEE which is 32 * 2 * 2048 = 131072 on mainnet
+  //  - with that and 32_000_000_000 MAX_EFFECTIVE_BALANCE, it still fits in a number given that Math.floor(Number.MAX_SAFE_INTEGER / 32_000_000_000) = 281474
+  //  - we don't need to compute the total slashings from state.slashings, it's handled by totalSlashingsByIncrement in EpochCache
   const slashingIndex = epoch % EPOCHS_PER_SLASHINGS_VECTOR;
   state.slashings.set(slashingIndex, (state.slashings.get(slashingIndex) ?? 0) + effectiveBalance);
   epochCtx.totalSlashingsByIncrement += effectiveBalanceIncrements[slashedIndex];

diff --git a/packages/types/src/phase0/sszTypes.ts b/packages/types/src/phase0/sszTypes.ts
@@ -247,6 +247,13 @@ export const Validator = ValidatorNodeStruct;
 export const Validators = new ListCompositeType(ValidatorNodeStruct, VALIDATOR_REGISTRY_LIMIT);
 export const Balances = new ListBasicType(UintNum64, VALIDATOR_REGISTRY_LIMIT);
 export const RandaoMixes = new VectorCompositeType(Bytes32, EPOCHS_PER_HISTORICAL_VECTOR);
+/**
+ * This is initially a Gwei (BigInt) vector, however since Nov 2023 it's converted to UintNum64 (number) vector in the state transition because:
+ * - state.slashings[nextEpoch % EPOCHS_PER_SLASHINGS_VECTOR] is reset per epoch in processSlashingsReset()
+ * - max slashed validators per epoch is SLOTS_PER_EPOCH * MAX_ATTESTER_SLASHINGS * MAX_VALIDATORS_PER_COMMITTEE which is 32 * 2 * 2048 = 131072 on mainnet
+ * - with that and 32_000_000_000 MAX_EFFECTIVE_BALANCE, it still fits in a number given that Math.floor(Number.MAX_SAFE_INTEGER / 32_000_000_000) = 281474
+ * - we don't need to compute the total slashings from state.slashings, it's handled by totalSlashingsByIncrement in EpochCache
+ */
 export const Slashings = new VectorBasicType(UintNum64, EPOCHS_PER_SLASHINGS_VECTOR);
 export const JustificationBits = new BitVectorType(JUSTIFICATION_BITS_LENGTH);