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Fix PerThing::from_percent. #7701

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merged 4 commits into from
Dec 11, 2020
Merged

Fix PerThing::from_percent. #7701

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a0cffc7
Fix overflow in per_things::from_percent.
kianenigma Dec 9, 2020
549aa6e
Fix test
kianenigma Dec 9, 2020
d8359e6
Fix the whole thing.. :|
kianenigma Dec 10, 2020
7207540
Merge branch 'master' of github.com:paritytech/substrate into kiz-fix…
kianenigma Dec 10, 2020
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22 changes: 15 additions & 7 deletions primitives/arithmetic/src/per_things.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -61,13 +61,11 @@ pub trait PerThing:
fn is_one(&self) -> bool { self.deconstruct() == Self::ACCURACY }

/// Build this type from a percent. Equivalent to `Self::from_parts(x * Self::ACCURACY / 100)`
/// but more accurate.
/// but more accurate and can cope with potential type overflows.
fn from_percent(x: Self::Inner) -> Self {
let a = x.min(100.into());
let b = Self::ACCURACY;
// if Self::ACCURACY % 100 > 0 then we need the correction for accuracy
let c = rational_mul_correction::<Self::Inner, Self>(b, a, 100.into(), Rounding::Nearest);
Self::from_parts(a / 100.into() * b + c)
let a: Self::Inner = x.min(100.into());
let b: Self::Inner = 100.into();
Self::from_rational_approximation(a, b)
}

/// Return the product of multiplication of this value by itself.
Expand Down Expand Up @@ -334,7 +332,7 @@ macro_rules! implement_per_thing {
&self.0
}
fn decode_from(x: Self::As) -> Self {
// Saturates if `x` is more than `$max` internally.
// Saturates if `x` is more than `$max` internally.
Self::from_parts(x)
}
}
Expand Down Expand Up @@ -707,6 +705,7 @@ macro_rules! implement_per_thing {

assert_eq!($name::from_percent(0), $name::from_parts(Zero::zero()));
assert_eq!($name::from_percent(10), $name::from_parts($max / 10));
assert_eq!($name::from_percent(50), $name::from_parts($max / 2));
assert_eq!($name::from_percent(100), $name::from_parts($max));
assert_eq!($name::from_percent(200), $name::from_parts($max));

Expand All @@ -717,6 +716,15 @@ macro_rules! implement_per_thing {
assert_eq!($name::from_fraction(-1.0), $name::from_parts(Zero::zero()));
}

#[test]
fn percent_trait_impl_works() {
assert_eq!(<$name as PerThing>::from_percent(0), $name::from_parts(Zero::zero()));
assert_eq!(<$name as PerThing>::from_percent(10), $name::from_parts($max / 10));
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As the macro is not exported. However you are just lucky that this works :P

assert_eq!(<$name as PerThing>::from_percent(50), $name::from_parts($max / 2));
assert_eq!(<$name as PerThing>::from_percent(100), $name::from_parts($max));
assert_eq!(<$name as PerThing>::from_percent(200), $name::from_parts($max));
}

macro_rules! u256ify {
($val:expr) => {
Into::<U256>::into($val)
Expand Down