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Staking module: approximate fraction into perbill to avoid overflow (#2889)

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* approximate fraction into perbill

* test

* fix comment

* line width

* bump impl version

* rename test for better naming

* test overflow

* Apply suggestions from code review

Co-Authored-By: Niklas Adolfsson <niklasadolfsson1@gmail.com>
This commit is contained in:
thiolliere
2019-06-24 13:23:54 +02:00
committed by Gavin Wood
parent e919d03331
commit cf7dbe8151
4 changed files with 112 additions and 25 deletions
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substrate/srml/staking/src/lib.rs
+8 -8
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@@ -940,11 +940,10 @@ impl<T: Trait> Module<T> {
// The total to be slashed from the nominators.
let total = exposure.total - exposure.own;
if !total.is_zero() {
// FIXME #1572 avoid overflow
let safe_mul_rational = |b| b * rest_slash / total;
for i in exposure.others.iter() {
let per_u64 = Perbill::from_rational_approximation(i.value, total);
// best effort - not much that can be done on fail.
imbalance.subsume(T::Currency::slash(&i.who, safe_mul_rational(i.value)).0)
imbalance.subsume(T::Currency::slash(&i.who, per_u64 * rest_slash).0)
}
}
}
@@ -986,13 +985,14 @@ impl<T: Trait> Module<T> {
} else {
let exposure = Self::stakers(stash);
let total = exposure.total.max(One::one());
// FIXME #1572: avoid overflow
let safe_mul_rational = |b| b * reward / total;
for i in &exposure.others {
let nom_payout = safe_mul_rational(i.value);
imbalance.maybe_subsume(Self::make_payout(&i.who, nom_payout));
let per_u64 = Perbill::from_rational_approximation(i.value, total);
imbalance.maybe_subsume(Self::make_payout(&i.who, per_u64 * reward));
}
safe_mul_rational(exposure.own)
let per_u64 = Perbill::from_rational_approximation(exposure.own, total);
per_u64 * reward
};
imbalance.maybe_subsume(Self::make_payout(stash, validator_cut + off_the_table));
T::Reward::on_unbalanced(imbalance);