Add comments about truncation

x/distribution/keeper/delegation.go

@@ -16,6 +16,7 @@ func (k Keeper) initializeDelegation(ctx sdk.Context, val sdk.ValAddress, del sd
 
  // calculate delegation stake in tokens
  // we don't store directly, so multiply delegation shares * (tokens per share)
+ // note: necessary to truncate so we don't allow withdrawing more rewards than owed
  stake := delegation.GetShares().MulTruncate(validator.GetDelegatorShareExRate())
  k.SetDelegatorStartingInfo(ctx, val, del, types.NewDelegatorStartingInfo(previousPeriod, stake, uint64(ctx.BlockHeight())))
 }
@@ -32,6 +33,7 @@ func (k Keeper) calculateDelegationRewardsBetween(ctx sdk.Context, val sdk.Valid
  starting := k.GetValidatorHistoricalRewards(ctx, val.GetOperator(), startingPeriod)
  ending := k.GetValidatorHistoricalRewards(ctx, val.GetOperator(), endingPeriod)
  difference := ending.CumulativeRewardRatio.Minus(starting.CumulativeRewardRatio)
+ // note: necessary to truncate so we don't allow withdrawing more rewards than owed
  rewards = difference.MulDecTruncate(stake)
  return
 }
@@ -54,6 +56,7 @@ func (k Keeper) calculateDelegationRewards(ctx sdk.Context, val sdk.Validator, d
  func(height uint64, event types.ValidatorSlashEvent) (stop bool) {
  endingPeriod := event.ValidatorPeriod
  rewards = rewards.Plus(k.calculateDelegationRewardsBetween(ctx, val, startingPeriod, endingPeriod, stake))
+ // note: necessary to truncate so we don't allow withdrawing more rewards than owed
  stake = stake.MulTruncate(sdk.OneDec().Sub(event.Fraction))
  startingPeriod = endingPeriod
  return false

x/distribution/keeper/validator.go

@@ -38,6 +38,7 @@ func (k Keeper) incrementValidatorPeriod(ctx sdk.Context, val sdk.Validator) uin
 
  current = sdk.DecCoins{}
  } else {
+ // note: necessary to truncate so we don't allow withdrawing more rewards than owed
  current = rewards.Rewards.QuoDecTruncate(sdk.NewDecFromInt(val.GetTokens()))
  }