mirror of
https://github.com/pezkuwichain/pezkuwi-subxt.git
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Squirrel
bc2e5e1fe2
First in a series of PRs that reduces our use of sp-std with a view to deprecating it. This is just looking at /substrate and moving some of the references from `sp-std` to `core`. These particular changes should be uncontroversial. Where macros are used `::core` should be used to remove any ambiguity. part of https://github.com/paritytech/polkadot-sdk/issues/2101
122 lines
3.4 KiB
Rust
122 lines
3.4 KiB
Rust
// This file is part of Substrate.
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// Copyright (C) Parity Technologies (UK) Ltd.
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// SPDX-License-Identifier: Apache-2.0
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//! Voting thresholds.
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use crate::Tally;
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use codec::{Decode, Encode, MaxEncodedLen};
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use core::ops::{Add, Div, Mul, Rem};
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use scale_info::TypeInfo;
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#[cfg(feature = "std")]
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use serde::{Deserialize, Serialize};
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use sp_runtime::traits::{IntegerSquareRoot, Zero};
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/// A means of determining if a vote is past pass threshold.
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#[derive(
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Clone, Copy, PartialEq, Eq, Encode, MaxEncodedLen, Decode, sp_runtime::RuntimeDebug, TypeInfo,
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)]
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#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
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pub enum VoteThreshold {
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/// A supermajority of approvals is needed to pass this vote.
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SuperMajorityApprove,
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/// A supermajority of rejects is needed to fail this vote.
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SuperMajorityAgainst,
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/// A simple majority of approvals is needed to pass this vote.
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SimpleMajority,
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}
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pub trait Approved<Balance> {
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/// Given a `tally` of votes and a total size of `electorate`, this returns `true` if the
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/// overall outcome is in favor of approval according to `self`'s threshold method.
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fn approved(&self, tally: Tally<Balance>, electorate: Balance) -> bool;
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}
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/// Return `true` iff `n1 / d1 < n2 / d2`. `d1` and `d2` may not be zero.
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fn compare_rationals<
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T: Zero + Mul<T, Output = T> + Div<T, Output = T> + Rem<T, Output = T> + Ord + Copy,
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>(
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mut n1: T,
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mut d1: T,
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mut n2: T,
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mut d2: T,
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) -> bool {
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// Uses a continued fractional representation for a non-overflowing compare.
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// Detailed at https://janmr.com/blog/2014/05/comparing-rational-numbers-without-overflow/.
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loop {
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let q1 = n1 / d1;
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let q2 = n2 / d2;
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if q1 < q2 {
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return true
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}
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if q2 < q1 {
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return false
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}
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let r1 = n1 % d1;
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let r2 = n2 % d2;
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if r2.is_zero() {
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return false
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}
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if r1.is_zero() {
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return true
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}
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n1 = d2;
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n2 = d1;
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d1 = r2;
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d2 = r1;
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}
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}
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impl<
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Balance: IntegerSquareRoot
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+ Zero
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+ Ord
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+ Add<Balance, Output = Balance>
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+ Mul<Balance, Output = Balance>
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+ Div<Balance, Output = Balance>
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+ Rem<Balance, Output = Balance>
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+ Copy,
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> Approved<Balance> for VoteThreshold
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{
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fn approved(&self, tally: Tally<Balance>, electorate: Balance) -> bool {
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let sqrt_voters = tally.turnout.integer_sqrt();
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let sqrt_electorate = electorate.integer_sqrt();
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if sqrt_voters.is_zero() {
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return false
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}
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match *self {
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VoteThreshold::SuperMajorityApprove =>
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compare_rationals(tally.nays, sqrt_voters, tally.ayes, sqrt_electorate),
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VoteThreshold::SuperMajorityAgainst =>
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compare_rationals(tally.nays, sqrt_electorate, tally.ayes, sqrt_voters),
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VoteThreshold::SimpleMajority => tally.ayes > tally.nays,
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn should_work() {
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assert!(!VoteThreshold::SuperMajorityApprove
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.approved(Tally { ayes: 60, nays: 50, turnout: 110 }, 210));
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assert!(VoteThreshold::SuperMajorityApprove
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.approved(Tally { ayes: 100, nays: 50, turnout: 150 }, 210));
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}
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}
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