stake: Allow stakes with unmatched credits observed to merge (#18985)
* stake: Allow stakes with unmatched credits observed to merge * Address feedback * Remove branch by doing a ceiling in one calc
This commit is contained in:
Jon Cinque
GitHub
@ -25,6 +25,7 @@ solana-config-program = { path = "../config", version = "=1.8.0" }
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thiserror = "1.0"
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[dev-dependencies]
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proptest = "1.0"
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solana-logger = { path = "../../logger", version = "=1.8.0" }
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[build-dependencies]
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@ -8,6 +8,7 @@ use {
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account::{AccountSharedData, ReadableAccount, WritableAccount},
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account_utils::{State, StateMut},
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clock::{Clock, Epoch},
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feature_set::stake_merge_with_unmatched_credits_observed,
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ic_msg,
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instruction::{checked_add, InstructionError},
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keyed_account::KeyedAccount,
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@ -957,6 +958,7 @@ impl MergeKind {
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}
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}
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// Remove this when the `stake_merge_with_unmatched_credits_observed` feature is removed
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fn active_stakes_can_merge(
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invoke_context: &dyn InvokeContext,
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stake: &Stake,
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@ -988,7 +990,19 @@ impl MergeKind {
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Self::metas_can_merge(invoke_context, self.meta(), source.meta(), clock)?;
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self.active_stake()
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.zip(source.active_stake())
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.map(|(stake, source)| Self::active_stakes_can_merge(invoke_context, stake, source))
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.map(|(stake, source)| {
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if invoke_context
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.is_feature_active(&stake_merge_with_unmatched_credits_observed::id())
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{
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Self::active_delegations_can_merge(
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invoke_context,
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&stake.delegation,
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&source.delegation,
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)
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} else {
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Self::active_stakes_can_merge(invoke_context, stake, source)
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}
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})
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.unwrap_or(Ok(()))?;
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let merged_state = match (self, source) {
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(Self::Inactive(_, _), Self::Inactive(_, _)) => None,
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@ -1005,7 +1019,12 @@ impl MergeKind {
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source_meta.rent_exempt_reserve,
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source_stake.delegation.stake,
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)?;
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stake.delegation.stake = checked_add(stake.delegation.stake, source_lamports)?;
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merge_delegation_stake_and_credits_observed(
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invoke_context,
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&mut stake,
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source_lamports,
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source_stake.credits_observed,
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)?;
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Some(StakeState::Stake(meta, stake))
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}
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(Self::FullyActive(meta, mut stake), Self::FullyActive(_, source_stake)) => {
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@ -1013,8 +1032,12 @@ impl MergeKind {
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// protect against the magic activation loophole. It will
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// instead be moved into the destination account as extra,
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// withdrawable `lamports`
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stake.delegation.stake =
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checked_add(stake.delegation.stake, source_stake.delegation.stake)?;
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merge_delegation_stake_and_credits_observed(
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invoke_context,
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&mut stake,
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source_stake.delegation.stake,
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source_stake.credits_observed,
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)?;
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Some(StakeState::Stake(meta, stake))
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}
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_ => return Err(StakeError::MergeMismatch.into()),
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@ -1023,6 +1046,69 @@ impl MergeKind {
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}
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}
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fn merge_delegation_stake_and_credits_observed(
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invoke_context: &dyn InvokeContext,
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stake: &mut Stake,
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absorbed_lamports: u64,
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absorbed_credits_observed: u64,
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) -> Result<(), InstructionError> {
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if invoke_context.is_feature_active(&stake_merge_with_unmatched_credits_observed::id()) {
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stake.credits_observed =
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stake_weighted_credits_observed(stake, absorbed_lamports, absorbed_credits_observed)
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.ok_or(InstructionError::ArithmeticOverflow)?;
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}
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stake.delegation.stake = checked_add(stake.delegation.stake, absorbed_lamports)?;
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Ok(())
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}
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/// Calculate the effective credits observed for two stakes when merging
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///
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/// When merging two `ActivationEpoch` or `FullyActive` stakes, the credits
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/// observed of the merged stake is the weighted average of the two stakes'
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/// credits observed.
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///
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/// This is because we can derive the effective credits_observed by reversing the staking
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/// rewards equation, _while keeping the rewards unchanged after merge (i.e. strong
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/// requirement)_, like below:
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///
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/// a(N) => account, r => rewards, s => stake, c => credits:
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/// assume:
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/// a3 = merge(a1, a2)
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/// then:
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/// a3.s = a1.s + a2.s
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///
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/// Next, given:
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/// aN.r = aN.c * aN.s (for every N)
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/// finally:
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/// a3.r = a1.r + a2.r
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/// a3.c * a3.s = a1.c * a1.s + a2.c * a2.s
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/// a3.c = (a1.c * a1.s + a2.c * a2.s) / (a1.s + a2.s) // QED
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///
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/// (For this discussion, we omitted irrelevant variables, including distance
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/// calculation against vote_account and point indirection.)
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fn stake_weighted_credits_observed(
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stake: &Stake,
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absorbed_lamports: u64,
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absorbed_credits_observed: u64,
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) -> Option<u64> {
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if stake.credits_observed == absorbed_credits_observed {
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Some(stake.credits_observed)
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} else {
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let total_stake = u128::from(stake.delegation.stake.checked_add(absorbed_lamports)?);
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let stake_weighted_credits =
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u128::from(stake.credits_observed).checked_mul(u128::from(stake.delegation.stake))?;
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let absorbed_weighted_credits =
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u128::from(absorbed_credits_observed).checked_mul(u128::from(absorbed_lamports))?;
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// Discard fractional credits as a merge side-effect friction by taking
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// the ceiling, done by adding `denominator - 1` to the numerator.
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let total_weighted_credits = stake_weighted_credits
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.checked_add(absorbed_weighted_credits)?
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.checked_add(total_stake)?
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.checked_sub(1)?;
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u64::try_from(total_weighted_credits.checked_div(total_stake)?).ok()
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}
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}
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// utility function, used by runtime
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// returns a tuple of (stakers_reward,voters_reward)
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pub fn redeem_rewards(
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@ -1281,6 +1367,7 @@ fn do_create_account(
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#[cfg(test)]
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mod tests {
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use super::*;
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use proptest::prelude::*;
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use solana_sdk::{
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account::{AccountSharedData, WritableAccount},
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clock::UnixTimestamp,
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@ -6649,4 +6736,187 @@ mod tests {
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let delegation = new_state.delegation().unwrap();
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assert_eq!(delegation.stake, 2 * stake.delegation.stake);
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}
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#[test]
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fn test_active_stake_merge() {
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let delegation_a = 4_242_424_242u64;
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let delegation_b = 6_200_000_000u64;
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let credits_a = 124_521_000u64;
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let rent_exempt_reserve = 227_000_000u64;
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let meta = Meta {
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rent_exempt_reserve,
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..Meta::default()
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};
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let stake_a = Stake {
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delegation: Delegation {
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stake: delegation_a,
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..Delegation::default()
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},
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credits_observed: credits_a,
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};
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let stake_b = Stake {
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delegation: Delegation {
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stake: delegation_b,
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..Delegation::default()
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},
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credits_observed: credits_a,
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};
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let invoke_context = MockInvokeContext::new(vec![]);
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// activating stake merge, match credits observed
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let activation_epoch_a = MergeKind::ActivationEpoch(meta, stake_a);
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let activation_epoch_b = MergeKind::ActivationEpoch(meta, stake_b);
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let new_stake = activation_epoch_a
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.merge(&invoke_context, activation_epoch_b, None)
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.unwrap()
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.unwrap()
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.stake()
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.unwrap();
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assert_eq!(new_stake.credits_observed, credits_a);
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assert_eq!(
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new_stake.delegation.stake,
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delegation_a + delegation_b + rent_exempt_reserve
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);
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// active stake merge, match credits observed
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let fully_active_a = MergeKind::FullyActive(meta, stake_a);
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let fully_active_b = MergeKind::FullyActive(meta, stake_b);
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let new_stake = fully_active_a
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.merge(&invoke_context, fully_active_b, None)
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.unwrap()
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.unwrap()
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.stake()
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.unwrap();
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assert_eq!(new_stake.credits_observed, credits_a);
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assert_eq!(new_stake.delegation.stake, delegation_a + delegation_b);
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// activating stake merge, unmatched credits observed
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let credits_b = 125_124_521u64;
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let stake_b = Stake {
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delegation: Delegation {
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stake: delegation_b,
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..Delegation::default()
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},
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credits_observed: credits_b,
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};
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let activation_epoch_a = MergeKind::ActivationEpoch(meta, stake_a);
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let activation_epoch_b = MergeKind::ActivationEpoch(meta, stake_b);
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let new_stake = activation_epoch_a
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.merge(&invoke_context, activation_epoch_b, None)
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.unwrap()
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.unwrap()
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.stake()
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.unwrap();
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assert_eq!(
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new_stake.credits_observed,
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(credits_a * delegation_a + credits_b * (delegation_b + rent_exempt_reserve))
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/ (delegation_a + delegation_b + rent_exempt_reserve)
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+ 1
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);
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assert_eq!(
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new_stake.delegation.stake,
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delegation_a + delegation_b + rent_exempt_reserve
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);
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// active stake merge, unmatched credits observed
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let fully_active_a = MergeKind::FullyActive(meta, stake_a);
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let fully_active_b = MergeKind::FullyActive(meta, stake_b);
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let new_stake = fully_active_a
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.merge(&invoke_context, fully_active_b, None)
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.unwrap()
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.unwrap()
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.stake()
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.unwrap();
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assert_eq!(
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new_stake.credits_observed,
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(credits_a * delegation_a + credits_b * delegation_b) / (delegation_a + delegation_b)
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+ 1
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);
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assert_eq!(new_stake.delegation.stake, delegation_a + delegation_b);
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// active stake merge, unmatched credits observed, no need to ceiling the calculation
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let delegation = 1_000_000u64;
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let credits_a = 200_000_000u64;
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let credits_b = 100_000_000u64;
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let rent_exempt_reserve = 227_000_000u64;
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let meta = Meta {
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rent_exempt_reserve,
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..Meta::default()
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};
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let stake_a = Stake {
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delegation: Delegation {
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stake: delegation,
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..Delegation::default()
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},
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credits_observed: credits_a,
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};
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let stake_b = Stake {
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delegation: Delegation {
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stake: delegation,
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..Delegation::default()
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},
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credits_observed: credits_b,
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};
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let fully_active_a = MergeKind::FullyActive(meta, stake_a);
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let fully_active_b = MergeKind::FullyActive(meta, stake_b);
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let new_stake = fully_active_a
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.merge(&invoke_context, fully_active_b, None)
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.unwrap()
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.unwrap()
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.stake()
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.unwrap();
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assert_eq!(
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new_stake.credits_observed,
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(credits_a * delegation + credits_b * delegation) / (delegation + delegation)
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);
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assert_eq!(new_stake.delegation.stake, delegation * 2);
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}
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prop_compose! {
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pub fn sum_within(max: u64)(total in 1..max)
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(intermediate in 1..total, total in Just(total))
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-> (u64, u64) {
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(intermediate, total - intermediate)
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}
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}
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proptest! {
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#[test]
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fn test_stake_weighted_credits_observed(
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(credits_a, credits_b) in sum_within(u64::MAX),
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(delegation_a, delegation_b) in sum_within(u64::MAX),
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) {
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let stake = Stake {
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delegation: Delegation {
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stake: delegation_a,
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..Delegation::default()
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},
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credits_observed: credits_a
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};
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let credits_observed = stake_weighted_credits_observed(
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&stake,
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delegation_b,
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credits_b,
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).unwrap();
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// calculated credits observed should always be between the credits of a and b
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if credits_a < credits_b {
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assert!(credits_a < credits_observed);
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assert!(credits_observed <= credits_b);
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} else {
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assert!(credits_b <= credits_observed);
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assert!(credits_observed <= credits_a);
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}
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// the difference of the combined weighted credits and the separate weighted credits
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// should be 1 or 0
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let weighted_credits_total = credits_observed as u128 * (delegation_a + delegation_b) as u128;
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let weighted_credits_a = credits_a as u128 * delegation_a as u128;
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let weighted_credits_b = credits_b as u128 * delegation_b as u128;
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let raw_diff = weighted_credits_total - (weighted_credits_a + weighted_credits_b);
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let credits_observed_diff = raw_diff / (delegation_a + delegation_b) as u128;
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assert!(credits_observed_diff <= 1);
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}
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}
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}
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Reference in New Issue
Block a user