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Prettify votes_needed #911

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Prettify votes_needed #911

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cb165ec
Prettify votes_needed implementation
webmaster128 Oct 12, 2024
2f6f3a0
Increase test coverage of votes_needed
webmaster128 Oct 13, 2024
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41 changes: 32 additions & 9 deletions packages/cw3/src/proposal.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,10 +4,6 @@ use cw_utils::{Expiration, Threshold};

use crate::{DepositInfo, Status, Vote};

// we multiply by this when calculating needed_votes in order to round up properly
// Note: `10u128.pow(9)` fails as "u128::pow` is not yet stable as a const fn"
const PRECISION_FACTOR: u128 = 1_000_000_000;

#[cw_serde]
pub struct Proposal {
pub title: String,
Expand Down Expand Up @@ -155,12 +151,13 @@ impl Votes {
}
}

// this is a helper function so Decimal works with u64 rather than Uint128
// also, we must *round up* here, as we need 8, not 7 votes to reach 50% of 15 total
// This is a helper function so Decimal works with u64 rather than Uint128.
// Also, we must *round up* here, as we need 8, not 7 votes to reach 50% of 15 total.
// `percentage` must not exceed 1.0.
fn votes_needed(weight: u64, percentage: Decimal) -> u64 {
let applied = Uint128::new(PRECISION_FACTOR * weight as u128).mul_floor(percentage);
// Divide by PRECISION_FACTOR, rounding up to the nearest integer
((applied.u128() + PRECISION_FACTOR - 1) / PRECISION_FACTOR) as u64
assert!(percentage <= Decimal::one());
let out = Uint128::from(weight).mul_ceil(percentage);
out.u128() as u64 // cast is safe because percentage is <= 1.
}

// we cast a ballot with our chosen vote and a given weight
Expand Down Expand Up @@ -199,10 +196,36 @@ mod test {
// round up right over 1
assert_eq!(2, votes_needed(3, Decimal::permille(334)));
assert_eq!(11, votes_needed(30, Decimal::permille(334)));
// round up to full number of votes
assert_eq!(420, votes_needed(420, Decimal::permille(999)));

// exact matches don't round
assert_eq!(17, votes_needed(34, Decimal::percent(50)));
assert_eq!(12, votes_needed(48, Decimal::percent(25)));

for x in [
0,
1,
2,
3,
10,
17,
456,
2020,
7697987,
18446744073709552,
u64::MAX,
] {
assert_eq!(votes_needed(x, Decimal::zero()), 0);
assert_eq!(votes_needed(x, Decimal::one()), x);
if x % 2 == 0 {
// even
assert_eq!(votes_needed(x, Decimal::percent(50)), x / 2);
} else {
// odd
assert_eq!(votes_needed(x, Decimal::percent(50)), x / 2 + 1);
}
}
}

fn setup_prop(
Expand Down