Refactor reward rate calculation

Author: xindingw

aptos-move/e2e-move-tests/src/tests/stake.rs

@@ -245,13 +245,12 @@ fn test_staking_rewards() {
         rewards_rate_denominator,
     );
 
-    // Another 0.5 year passed. Rewards rate halves. New rewards rate is 0.5% every epoch.
+    // Another 0.5 year passed. Rewards rate halves. New rewards after this epoch rate is 0.5% every epoch.
     // Both validators propose a block in the current epoch. Both should receive rewards.
     harness.new_block_with_metadata(validator_1_address, vec![]);
     harness.new_block_with_metadata(validator_2_address, vec![]);
     harness.fast_forward(one_year_in_secs / 2);
     harness.new_epoch();
-    rewards_rate = rewards_rate * rewards_rate_decrease_rate_bps / bps_denominator;
     update_stake_amount_and_assert_with_errors(
         &mut harness,
         &mut stake_amount_1,
@@ -266,12 +265,32 @@ fn test_staking_rewards() {
         rewards_rate,
         rewards_rate_denominator,
     );
+    rewards_rate = rewards_rate * rewards_rate_decrease_rate_bps / bps_denominator;
 
+    // Another new epoch, both validators receive rewards in 0.5% every epoch.
     // Another year passed. Rewards rate halves but it cannot be lower than 0.3%.
-    // New rewards rate is 0.3% every epoch.
+    // New rewards rate of the next epoch is 0.3% every epoch.
+    harness.new_block_with_metadata(validator_1_address, vec![]);
+    harness.new_block_with_metadata(validator_2_address, vec![]);
+    harness.fast_forward(one_year_in_secs);
+    harness.new_epoch();
+    update_stake_amount_and_assert_with_errors(
+        &mut harness,
+        &mut stake_amount_1,
+        validator_1_address,
+        rewards_rate,
+        rewards_rate_denominator,
+    );
+    update_stake_amount_and_assert_with_errors(
+        &mut harness,
+        &mut stake_amount_2,
+        validator_2_address,
+        rewards_rate,
+        rewards_rate_denominator,
+    );
+
     // Validator 1 misses one proposal but has one successful so they receive half of the rewards.
     harness.new_block_with_metadata(validator_1_address, vec![index_1]);
-    harness.fast_forward(one_year_in_secs);
     harness.new_epoch();
     rewards_rate = min_rewards_rate / 2;
     update_stake_amount_and_assert_with_errors(

aptos-move/framework/aptos-framework/doc/gas_schedule.md

@@ -319,7 +319,7 @@ This can be called by on-chain governance to update the gas schedule.
 
 
 
-<pre><code><b>pragma</b> timeout = 60;
+<pre><code><b>pragma</b> timeout = 100;
 <b>requires</b> <b>exists</b>&lt;<a href="stake.md#0x1_stake_ValidatorFees">stake::ValidatorFees</a>&gt;(@aptos_framework);
 <b>requires</b> <b>exists</b>&lt;CoinInfo&lt;AptosCoin&gt;&gt;(@aptos_framework);
 <b>include</b> <a href="system_addresses.md#0x1_system_addresses_AbortsIfNotAptosFramework">system_addresses::AbortsIfNotAptosFramework</a>{ <a href="account.md#0x1_account">account</a>: aptos_framework };

aptos-move/framework/aptos-framework/doc/stake.md

@@ -3060,6 +3060,11 @@ power.
 
         validator_index = validator_index + 1;
     };
+
+    <b>if</b> (<a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_periodical_reward_rate_decrease_enabled">features::periodical_reward_rate_decrease_enabled</a>()) {
+        // Update rewards rate after reward distribution.
+        <a href="staking_config.md#0x1_staking_config_calculate_and_save_latest_epoch_rewards_rate">staking_config::calculate_and_save_latest_epoch_rewards_rate</a>();
+    };
 }
 </code></pre>
 
@@ -3102,23 +3107,7 @@ This function shouldn't abort.
         <b>assume</b> cur_validator_perf.successful_proposals + cur_validator_perf.failed_proposals &lt;= <a href="stake.md#0x1_stake_MAX_U64">MAX_U64</a>;
     };
     <b>let</b> num_total_proposals = cur_validator_perf.successful_proposals + cur_validator_perf.failed_proposals;
-    <b>let</b> (rewards_rate, rewards_rate_denominator) = <b>if</b> (<a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_periodical_reward_rate_decrease_enabled">features::periodical_reward_rate_decrease_enabled</a>()) {
-        <b>let</b> epoch_rewards_rate = <a href="staking_config.md#0x1_staking_config_calculate_and_save_latest_epoch_rewards_rate">staking_config::calculate_and_save_latest_epoch_rewards_rate</a>();
-        <b>if</b> (<a href="../../aptos-stdlib/doc/fixed_point64.md#0x1_fixed_point64_is_zero">fixed_point64::is_zero</a>(epoch_rewards_rate)) {
-            (0u64, 1u64)
-        } <b>else</b> {
-            // Maximize denominator for higher precision.
-            // Restriction: nominator &lt;= <a href="stake.md#0x1_stake_MAX_REWARDS_RATE">MAX_REWARDS_RATE</a> && denominator &lt;= <a href="stake.md#0x1_stake_MAX_U64">MAX_U64</a>
-            <b>let</b> denominator = <a href="../../aptos-stdlib/doc/fixed_point64.md#0x1_fixed_point64_divide_u128">fixed_point64::divide_u128</a>((<a href="stake.md#0x1_stake_MAX_REWARDS_RATE">MAX_REWARDS_RATE</a> <b>as</b> u128), epoch_rewards_rate);
-            <b>if</b> (denominator &gt; <a href="stake.md#0x1_stake_MAX_U64">MAX_U64</a>) {
-                denominator = <a href="stake.md#0x1_stake_MAX_U64">MAX_U64</a>
-            };
-            <b>let</b> nominator = (<a href="../../aptos-stdlib/doc/fixed_point64.md#0x1_fixed_point64_multiply_u128">fixed_point64::multiply_u128</a>(denominator, epoch_rewards_rate) <b>as</b> u64);
-            (nominator, (denominator <b>as</b> u64))
-        }
-    } <b>else</b> {
-        <a href="staking_config.md#0x1_staking_config_get_reward_rate">staking_config::get_reward_rate</a>(<a href="staking_config.md#0x1_staking_config">staking_config</a>)
-    };
+    <b>let</b> (rewards_rate, rewards_rate_denominator) = <a href="staking_config.md#0x1_staking_config_get_reward_rate">staking_config::get_reward_rate</a>(<a href="staking_config.md#0x1_staking_config">staking_config</a>);
     <b>let</b> rewards_active = <a href="stake.md#0x1_stake_distribute_rewards">distribute_rewards</a>(
         &<b>mut</b> stake_pool.active,
         num_successful_proposals,
@@ -4229,7 +4218,7 @@ Returns validator's next epoch voting power, including pending_active, active, a
     <b>requires</b> <b>exists</b>&lt;<a href="stake.md#0x1_stake_ValidatorPerformance">ValidatorPerformance</a>&gt;(@aptos_framework);
     <b>requires</b> <b>exists</b>&lt;<a href="stake.md#0x1_stake_ValidatorSet">ValidatorSet</a>&gt;(@aptos_framework);
     <b>requires</b> <b>exists</b>&lt;StakingConfig&gt;(@aptos_framework);
-    <b>requires</b> <b>exists</b>&lt;StakingRewardsConfig&gt;(@aptos_framework) || !<a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_spec_reward_rate_decrease_enabled">features::spec_reward_rate_decrease_enabled</a>();
+    <b>requires</b> <b>exists</b>&lt;StakingRewardsConfig&gt;(@aptos_framework) || !<a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_spec_periodical_reward_rate_decrease_enabled">features::spec_periodical_reward_rate_decrease_enabled</a>();
     <b>requires</b> <b>exists</b>&lt;<a href="timestamp.md#0x1_timestamp_CurrentTimeMicroseconds">timestamp::CurrentTimeMicroseconds</a>&gt;(@aptos_framework);
     <b>requires</b> <b>exists</b>&lt;<a href="stake.md#0x1_stake_ValidatorFees">ValidatorFees</a>&gt;(@aptos_framework);
 }

aptos-move/framework/aptos-framework/doc/staking_config.md

@@ -175,6 +175,15 @@ Staking reward configurations that will be stored with the @aptos_framework acco
 ## Constants
 
 
+<a name="0x1_staking_config_MAX_U64"></a>
+
+
+
+<pre><code><b>const</b> <a href="staking_config.md#0x1_staking_config_MAX_U64">MAX_U64</a>: u128 = 18446744073709551615;
+</code></pre>
+
+
+
 <a name="0x1_staking_config_BPS_DENOMINATOR"></a>
 
 Denominator of number in basis points. 1 bps(basis points) = 0.01%.
@@ -536,8 +545,7 @@ withdraw all funds).
 
 ## Function `get_reward_rate`
 
-DEPRECATING
-Return the reward rate.
+Return the reward rate of this epoch.
 
 
 <pre><code><b>public</b> <b>fun</b> <a href="staking_config.md#0x1_staking_config_get_reward_rate">get_reward_rate</a>(config: &<a href="staking_config.md#0x1_staking_config_StakingConfig">staking_config::StakingConfig</a>): (u64, u64)
@@ -549,9 +557,25 @@ Return the reward rate.
 <summary>Implementation</summary>
 
 
-<pre><code><b>public</b> <b>fun</b> <a href="staking_config.md#0x1_staking_config_get_reward_rate">get_reward_rate</a>(config: &<a href="staking_config.md#0x1_staking_config_StakingConfig">StakingConfig</a>): (u64, u64) {
-    <b>assert</b>!(!<a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_periodical_reward_rate_decrease_enabled">features::periodical_reward_rate_decrease_enabled</a>(), <a href="staking_config.md#0x1_staking_config_EDEPRECATED_FUNCTION">EDEPRECATED_FUNCTION</a>);
-    (config.rewards_rate, config.rewards_rate_denominator)
+<pre><code><b>public</b> <b>fun</b> <a href="staking_config.md#0x1_staking_config_get_reward_rate">get_reward_rate</a>(config: &<a href="staking_config.md#0x1_staking_config_StakingConfig">StakingConfig</a>): (u64, u64) <b>acquires</b> <a href="staking_config.md#0x1_staking_config_StakingRewardsConfig">StakingRewardsConfig</a> {
+    <b>let</b> (rewards_rate, rewards_rate_denominator) = <b>if</b> (<a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_periodical_reward_rate_decrease_enabled">features::periodical_reward_rate_decrease_enabled</a>()) {
+        <b>let</b> epoch_rewards_rate = <b>borrow_global</b>&lt;<a href="staking_config.md#0x1_staking_config_StakingRewardsConfig">StakingRewardsConfig</a>&gt;(@aptos_framework).rewards_rate;
+        <b>if</b> (<a href="../../aptos-stdlib/doc/fixed_point64.md#0x1_fixed_point64_is_zero">fixed_point64::is_zero</a>(epoch_rewards_rate)) {
+            (0u64, 1u64)
+        } <b>else</b> {
+            // Maximize denominator for higher precision.
+            // Restriction: nominator &lt;= <a href="staking_config.md#0x1_staking_config_MAX_REWARDS_RATE">MAX_REWARDS_RATE</a> && denominator &lt;= <a href="staking_config.md#0x1_staking_config_MAX_U64">MAX_U64</a>
+            <b>let</b> denominator = <a href="../../aptos-stdlib/doc/fixed_point64.md#0x1_fixed_point64_divide_u128">fixed_point64::divide_u128</a>((<a href="staking_config.md#0x1_staking_config_MAX_REWARDS_RATE">MAX_REWARDS_RATE</a> <b>as</b> u128), epoch_rewards_rate);
+            <b>if</b> (denominator &gt; <a href="staking_config.md#0x1_staking_config_MAX_U64">MAX_U64</a>) {
+                denominator = <a href="staking_config.md#0x1_staking_config_MAX_U64">MAX_U64</a>
+            };
+            <b>let</b> nominator = (<a href="../../aptos-stdlib/doc/fixed_point64.md#0x1_fixed_point64_multiply_u128">fixed_point64::multiply_u128</a>(denominator, epoch_rewards_rate) <b>as</b> u64);
+            (nominator, (denominator <b>as</b> u64))
+        }
+    } <b>else</b> {
+        (config.rewards_rate, config.rewards_rate_denominator)
+    };
+    (rewards_rate, rewards_rate_denominator)
 }
 </code></pre>
 
@@ -1146,7 +1170,7 @@ StakingRewardsConfig does not exist under the aptos_framework before creating it
 
 
 
-<pre><code><b>aborts_if</b> <a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_spec_reward_rate_decrease_enabled">features::spec_reward_rate_decrease_enabled</a>();
+<pre><code><b>include</b> <a href="staking_config.md#0x1_staking_config_StakingRewardsConfigRequirement">StakingRewardsConfigRequirement</a>;
 </code></pre>
 
 
@@ -1163,7 +1187,7 @@ StakingRewardsConfig does not exist under the aptos_framework before creating it
 
 
 <pre><code><b>aborts_if</b> !<b>exists</b>&lt;<a href="staking_config.md#0x1_staking_config_StakingRewardsConfig">StakingRewardsConfig</a>&gt;(@aptos_framework);
-<b>aborts_if</b> !<a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_spec_reward_rate_decrease_enabled">features::spec_reward_rate_decrease_enabled</a>();
+<b>aborts_if</b> !<a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_spec_periodical_reward_rate_decrease_enabled">features::spec_periodical_reward_rate_decrease_enabled</a>();
 <b>include</b> <a href="staking_config.md#0x1_staking_config_StakingRewardsConfigRequirement">StakingRewardsConfigRequirement</a>;
 </code></pre>
 
@@ -1180,7 +1204,7 @@ StakingRewardsConfig does not exist under the aptos_framework before creating it
 
 
 
-<pre><code><b>requires</b> <a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_spec_reward_rate_decrease_enabled">features::spec_reward_rate_decrease_enabled</a>();
+<pre><code><b>requires</b> <a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_spec_periodical_reward_rate_decrease_enabled">features::spec_periodical_reward_rate_decrease_enabled</a>();
 <b>include</b> <a href="staking_config.md#0x1_staking_config_StakingRewardsConfigRequirement">StakingRewardsConfigRequirement</a>;
 <b>aborts_if</b> !<b>exists</b>&lt;<a href="staking_config.md#0x1_staking_config_StakingRewardsConfig">StakingRewardsConfig</a>&gt;(@aptos_framework);
 </code></pre>
@@ -1247,7 +1271,7 @@ The <code>rewards_rate</code> which is the numerator is limited to be <code>&lt;
 rewards_rate/rewards_rate_denominator <= 1.
 
 
-<pre><code><b>aborts_if</b> <a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_spec_reward_rate_decrease_enabled">features::spec_reward_rate_decrease_enabled</a>();
+<pre><code><b>aborts_if</b> <a href="../../aptos-stdlib/../move-stdlib/doc/features.md#0x1_features_spec_periodical_reward_rate_decrease_enabled">features::spec_periodical_reward_rate_decrease_enabled</a>();
 <b>let</b> addr = <a href="../../aptos-stdlib/../move-stdlib/doc/signer.md#0x1_signer_address_of">signer::address_of</a>(aptos_framework);
 <b>aborts_if</b> addr != @aptos_framework;
 <b>aborts_if</b> new_rewards_rate_denominator &lt;= 0;

aptos-move/framework/aptos-framework/sources/configs/gas_schedule.spec.move

@@ -44,7 +44,7 @@ spec aptos_framework::gas_schedule {
         use aptos_framework::transaction_fee;
         use aptos_framework::staking_config;
 
-        pragma timeout = 60;
+        pragma timeout = 100;
 
         requires exists<stake::ValidatorFees>(@aptos_framework);
         requires exists<CoinInfo<AptosCoin>>(@aptos_framework);

aptos-move/framework/aptos-framework/sources/configs/staking_config.move

@@ -42,6 +42,8 @@ module aptos_framework::staking_config {
     /// 1 year => 365 * 24 * 60 * 60
     const ONE_YEAR_IN_SECS: u64 = 31536000;
 
+    const MAX_U64: u128 = 18446744073709551615;
+
 
     /// Validator set configurations that will be stored with the @aptos_framework account.
     struct StakingConfig has copy, drop, key {
@@ -184,11 +186,26 @@ module aptos_framework::staking_config {
         config.recurring_lockup_duration_secs
     }
 
-    /// DEPRECATING
-    /// Return the reward rate.
-    public fun get_reward_rate(config: &StakingConfig): (u64, u64) {
-        assert!(!features::periodical_reward_rate_decrease_enabled(), EDEPRECATED_FUNCTION);
-        (config.rewards_rate, config.rewards_rate_denominator)
+    /// Return the reward rate of this epoch.
+    public fun get_reward_rate(config: &StakingConfig): (u64, u64) acquires StakingRewardsConfig {
+        let (rewards_rate, rewards_rate_denominator) = if (features::periodical_reward_rate_decrease_enabled()) {
+            let epoch_rewards_rate = borrow_global<StakingRewardsConfig>(@aptos_framework).rewards_rate;
+            if (fixed_point64::is_zero(epoch_rewards_rate)) {
+                (0u64, 1u64)
+            } else {
+                // Maximize denominator for higher precision.
+                // Restriction: nominator <= MAX_REWARDS_RATE && denominator <= MAX_U64
+                let denominator = fixed_point64::divide_u128((MAX_REWARDS_RATE as u128), epoch_rewards_rate);
+                if (denominator > MAX_U64) {
+                    denominator = MAX_U64
+                };
+                let nominator = (fixed_point64::multiply_u128(denominator, epoch_rewards_rate) as u64);
+                (nominator, (denominator as u64))
+            }
+        } else {
+            (config.rewards_rate, config.rewards_rate_denominator)
+        };
+        (rewards_rate, rewards_rate_denominator)
     }
 
     /// Return the joining limit %.

aptos-move/framework/aptos-framework/sources/configs/staking_config.spec.move

@@ -79,17 +79,17 @@ spec aptos_framework::staking_config {
     }
 
     spec get_reward_rate(config: &StakingConfig): (u64, u64) {
-        aborts_if features::spec_reward_rate_decrease_enabled();
+        include StakingRewardsConfigRequirement;
     }
 
     spec calculate_and_save_latest_epoch_rewards_rate(): FixedPoint64 {
         aborts_if !exists<StakingRewardsConfig>(@aptos_framework);
-        aborts_if !features::spec_reward_rate_decrease_enabled();
+        aborts_if !features::spec_periodical_reward_rate_decrease_enabled();
         include StakingRewardsConfigRequirement;
     }
 
     spec calculate_and_save_latest_rewards_config(): StakingRewardsConfig {
-        requires features::spec_reward_rate_decrease_enabled();
+        requires features::spec_periodical_reward_rate_decrease_enabled();
         include StakingRewardsConfigRequirement;
         aborts_if !exists<StakingRewardsConfig>(@aptos_framework);
     }
@@ -134,7 +134,7 @@ spec aptos_framework::staking_config {
         new_rewards_rate_denominator: u64,
     ) {
         use std::signer;
-        aborts_if features::spec_reward_rate_decrease_enabled();
+        aborts_if features::spec_periodical_reward_rate_decrease_enabled();
         let addr = signer::address_of(aptos_framework);
         aborts_if addr != @aptos_framework;
         aborts_if new_rewards_rate_denominator <= 0;
@@ -209,7 +209,7 @@ spec aptos_framework::staking_config {
 
     spec schema StakingRewardsConfigRequirement {
         requires exists<timestamp::CurrentTimeMicroseconds>(@aptos_framework);
-        include features::spec_reward_rate_decrease_enabled() ==> StakingRewardsConfigEnabledRequirement;
+        include features::spec_periodical_reward_rate_decrease_enabled() ==> StakingRewardsConfigEnabledRequirement;
     }
 
     spec schema StakingRewardsConfigEnabledRequirement {

aptos-move/framework/aptos-framework/sources/delegation_pool.move

@@ -990,6 +990,10 @@ module aptos_framework::delegation_pool {
 
     #[test_only]
     use aptos_framework::reconfiguration;
+    #[test_only]
+    use aptos_std::fixed_point64;
+    #[test_only]
+    use aptos_framework::timestamp::fast_forward_seconds;
 
     #[test_only]
     const CONSENSUS_KEY_1: vector<u8> = x"8a54b92288d4ba5073d3a52e80cc00ae9fbbc1cc5b433b46089b7804c38a76f00fc64746c7685ee628fc2d0b929c2294";
@@ -1317,6 +1321,40 @@ module aptos_framework::delegation_pool {
         // stakes should remain the same - `Self::get_stake` correctly calculates them
         synchronize_delegation_pool(pool_address);
         assert_delegation(delegator1_address, pool_address, 11201699216002, 0, 2000000000000);
+
+        let reward_period_start_time_in_sec = timestamp::now_seconds();
+        // Enable rewards rate decrease. Initially rewards rate is still 1% every epoch. Rewards rate halves every year.
+        let one_year_in_secs: u64 = 31536000;
+        staking_config::initialize_rewards(
+            aptos_framework,
+            fixed_point64::create_from_rational(2, 100),
+            fixed_point64::create_from_rational(6, 1000),
+            one_year_in_secs,
+            reward_period_start_time_in_sec,
+            fixed_point64::create_from_rational(50, 100),
+        );
+        features::change_feature_flags(aptos_framework, vector[features::get_periodical_reward_rate_decrease_feature()], vector[]);
+
+        // add more stake from delegator 1
+        stake::mint(delegator1, 20000 * ONE_APT);
+        let delegator1_pending_inactive: u64;
+        (delegator1_active, _, delegator1_pending_inactive) = get_stake(pool_address, delegator1_address);
+        fee = get_add_stake_fee(pool_address, 20000 * ONE_APT);
+        add_stake(delegator1, pool_address, 20000 * ONE_APT);
+
+        assert_delegation(delegator1_address, pool_address, delegator1_active + 20000 * ONE_APT - fee, 0, delegator1_pending_inactive);
+
+        // delegator 1 unlocks his entire newly added stake
+        unlock(delegator1, pool_address, 20000 * ONE_APT - fee);
+        end_aptos_epoch();
+        // delegator 1 should own previous 11201699216002 active * ~1.01253 and 20000 * ~1.01253 + 20000 coins pending_inactive
+        assert_delegation(delegator1_address, pool_address, 11342056366822, 0, 4025059974939);
+
+        // stakes should remain the same - `Self::get_stake` correctly calculates them
+        synchronize_delegation_pool(pool_address);
+        assert_delegation(delegator1_address, pool_address, 11342056366822, 0, 4025059974939);
+
+        fast_forward_seconds(one_year_in_secs);
     }
 
     #[test(aptos_framework = @aptos_framework, validator = @0x123, delegator = @0x010)]