Address clippy arith lints (#1038)

eth2/types/src/attestation.rs

@@ -3,6 +3,7 @@ use super::{
     Signature, SignedRoot, SubnetId,
 };
 use crate::{test_utils::TestRandom, Hash256};
+use safe_arith::{ArithError, SafeArith};
 
 use serde_derive::{Deserialize, Serialize};
 use ssz_derive::{Decode, Encode};
@@ -13,6 +14,7 @@ use tree_hash_derive::TreeHash;
 pub enum Error {
     SszTypesError(ssz_types::Error),
     AlreadySigned(usize),
+    SubnetCountIsZero(ArithError),
 }
 
 /// Details an attestation that can be slashable.
@@ -86,8 +88,12 @@ impl<T: EthSpec> Attestation<T> {
     ///
     /// Note, this will return the subnet id for an aggregated attestation. This is done
     /// to avoid checking aggregate bits every time we wish to get an id.
-    pub fn subnet_id(&self) -> SubnetId {
-        SubnetId::new(self.data.index % T::default_spec().attestation_subnet_count)
+    pub fn subnet_id(&self, spec: &ChainSpec) -> Result<SubnetId, Error> {
+        self.data
+            .index
+            .safe_rem(spec.attestation_subnet_count)
+            .map(SubnetId::new)
+            .map_err(Error::SubnetCountIsZero)
     }
 }
 

eth2/types/src/beacon_state.rs

@@ -485,7 +485,7 @@ impl<T: EthSpec> BeaconState<T> {
         let committee = self.get_beacon_committee(slot, index)?;
         let modulo = std::cmp::max(
             1,
-            committee.committee.len() as u64 / spec.target_aggregators_per_committee,
+            (committee.committee.len() as u64).safe_div(spec.target_aggregators_per_committee)?,
         );
         let signature_hash = hash(&slot_signature.as_bytes());
         let signature_hash_int = u64::from_le_bytes(
@@ -493,7 +493,8 @@ impl<T: EthSpec> BeaconState<T> {
                 .try_into()
                 .expect("first 8 bytes of signature should always convert to fixed array"),
         );
-        Ok(signature_hash_int % modulo == 0)
+
+        Ok(signature_hash_int.safe_rem(modulo)? == 0)
     }
 
     /// Returns the beacon proposer index for the `slot` in the given `relative_epoch`.

eth2/types/src/selection_proof.rs

@@ -1,4 +1,5 @@
 use crate::{ChainSpec, Domain, EthSpec, Fork, Hash256, SecretKey, Signature, SignedRoot, Slot};
+use safe_arith::{ArithError, SafeArith};
 use std::convert::TryInto;
 use tree_hash::TreeHash;
 
@@ -24,7 +25,7 @@ impl SelectionProof {
         Self(Signature::new(message.as_bytes(), secret_key))
     }
 
-    pub fn is_aggregator(&self, modulo: u64) -> bool {
+    pub fn is_aggregator(&self, modulo: u64) -> Result<bool, ArithError> {
         let signature_hash = self.0.tree_hash_root();
         let signature_hash_int = u64::from_le_bytes(
             signature_hash[0..8]
@@ -33,7 +34,7 @@ impl SelectionProof {
                 .expect("first 8 bytes of signature should always convert to fixed array"),
         );
 
-        signature_hash_int % modulo == 0
+        signature_hash_int.safe_rem(modulo).map(|rem| rem == 0)
     }
 }