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[framework] Refactor reward rate calculation #7867

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Apr 20, 2023
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[framework] Refactor reward rate calculation #7867

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27 changes: 23 additions & 4 deletions aptos-move/e2e-move-tests/src/tests/stake.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand All @@ -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(
Expand Down
2 changes: 1 addition & 1 deletion aptos-move/framework/aptos-framework/doc/gas_schedule.md
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Expand Up @@ -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 };
Expand Down
25 changes: 7 additions & 18 deletions aptos-move/framework/aptos-framework/doc/stake.md
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Expand Up @@ -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>

Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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);
}
Expand Down
42 changes: 33 additions & 9 deletions aptos-move/framework/aptos-framework/doc/staking_config.md
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Expand Up @@ -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%.
Expand Down Expand Up @@ -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)
Expand All @@ -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>

Expand Down Expand Up @@ -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>


Expand All @@ -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>

Expand All @@ -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>
Expand Down Expand Up @@ -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;
Expand Down
2 changes: 1 addition & 1 deletion aptos-move/framework/aptos-framework/sources/configs/gas_schedule.spec.move
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Expand Up @@ -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);
Expand Down
27 changes: 22 additions & 5 deletions aptos-move/framework/aptos-framework/sources/configs/staking_config.move
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Expand Up @@ -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 {
Expand Down Expand Up @@ -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 %.
Expand Down
10 changes: 5 additions & 5 deletions aptos-move/framework/aptos-framework/sources/configs/staking_config.spec.move
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
}
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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 {
Expand Down
38 changes: 38 additions & 0 deletions aptos-move/framework/aptos-framework/sources/delegation_pool.move
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Original file line number Diff line number Diff line change
Expand Up @@ -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";
Expand Down Expand Up @@ -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)]
Expand Down
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