runtime: Update CurrencyToVoteHandler.

runtime-modules/common/src/currency.rs

@@ -1,27 +0,0 @@
-use sp_runtime::traits::Convert;
-
-/// A structure that converts the currency type into a lossy u64
-/// And back from u128
-pub struct CurrencyToVoteHandler;
-
-impl Convert<u128, u64> for CurrencyToVoteHandler {
-    fn convert(x: u128) -> u64 {
-        if x >> 96 == 0 {
-            x as u64
-        } else {
-            u64::max_value()
-        }
-    }
-}
-
-impl Convert<u128, u128> for CurrencyToVoteHandler {
-    fn convert(x: u128) -> u128 {
-        // if it practically fits in u64
-        if x >> 64 == 0 {
-            x
-        } else {
-            // 0000_0000_FFFF_FFFF_FFFF_FFFF_0000_0000
-            u64::max_value() as u128
-        }
-    }
-}

runtime-modules/common/src/lib.rs

@@ -2,7 +2,6 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 pub mod constraints;
-pub mod currency;
 pub mod origin;
 pub mod working_group;
 

runtime/src/lib.rs

@@ -355,7 +355,7 @@ parameter_types! {
 impl pallet_staking::Trait for Runtime {
     type Currency = Balances;
     type UnixTime = Timestamp;
-    type CurrencyToVote = common::currency::CurrencyToVoteHandler;
+    type CurrencyToVote = CurrencyToVoteHandler;
     type RewardRemainder = (); // Could be Treasury.
     type Event = Event;
     type Slash = (); // Where to send the slashed funds. Could be Treasury.

runtime/src/runtime_api.rs

@@ -6,7 +6,7 @@ use pallet_transaction_payment_rpc_runtime_api::RuntimeDispatchInfo;
 use sp_api::impl_runtime_apis;
 use sp_core::crypto::KeyTypeId;
 use sp_core::OpaqueMetadata;
-use sp_runtime::traits::{BlakeTwo256, Block as BlockT, NumberFor};
+use sp_runtime::traits::{BlakeTwo256, Block as BlockT, Convert, NumberFor};
 use sp_runtime::{generic, ApplyExtrinsicResult};
 use sp_std::vec::Vec;
 
@@ -16,10 +16,32 @@ use crate::{
     GrandpaId, Hash, Index, RuntimeVersion, Signature, VERSION,
 };
 use crate::{
-    AllModules, AuthorityDiscovery, Babe, Call, Grandpa, Historical, InherentDataExt,
+    AllModules, AuthorityDiscovery, Babe, Balances, Call, Grandpa, Historical, InherentDataExt,
     RandomnessCollectiveFlip, Runtime, SessionKeys, System, TransactionPayment,
 };
 
+/// Struct that handles the conversion of Balance -> `u64`. This is used for staking's election
+/// calculation.
+pub struct CurrencyToVoteHandler;
+
+impl CurrencyToVoteHandler {
+    fn factor() -> Balance {
+        (Balances::total_issuance() / u64::max_value() as Balance).max(1)
+    }
+}
+
+impl Convert<Balance, u64> for CurrencyToVoteHandler {
+    fn convert(x: Balance) -> u64 {
+        (x / Self::factor()) as u64
+    }
+}
+
+impl Convert<u128, Balance> for CurrencyToVoteHandler {
+    fn convert(x: u128) -> Balance {
+        x * Self::factor()
+    }
+}
+
 /// The SignedExtension to the basic transaction logic.
 pub type SignedExtra = (
     frame_system::CheckSpecVersion<Runtime>,