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Precision::round improvements #21

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Precision::round improvements #21

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38089eb
Add tests for Precision::round
chipshort Apr 22, 2024
48bd12e
Improve Precise::round implementation
chipshort Apr 22, 2024
e525f23
Cleanup
chipshort Apr 23, 2024
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92 changes: 78 additions & 14 deletions packages/kujira-std/src/precision.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -34,17 +34,21 @@ impl Precise for Decimal {
fn round(&self, p: &Precision) -> Self {
match p {
Precision::SignificantFigures(sf) => {
// early return for zero significant figures
if sf == &0 {
return Self::zero();
}
let int = self.numerator();
let len = int.to_string().as_str().bytes().len() as u32;
let decimals: u32 = len - *sf as u32;
let pow = Uint128::from(10u128).pow(decimals);
let truncated = Self::from_ratio(int, pow) * Uint128::from(1u128);
Self::from_ratio(truncated * pow, self.denominator())
let figures = int.to_string().len() as u32;
let pow = Uint128::new(10u128).pow(figures - *sf as u32);
let significant_part = int / pow; // integer division truncates
let truncated = significant_part * pow;
Self::new(truncated)
}
Precision::DecimalPlaces(dp) => {
let pow = Uint128::from(10u128).pow(18 - *dp as u32);
let x = Self::from_ratio(self.numerator(), self.denominator() * pow);
Self::from_ratio(x.numerator() * pow, x.denominator())
let significant_part = self.numerator() / pow; // integer division truncates
Self::new(significant_part * pow)
}
}
}
Expand All @@ -54,17 +58,21 @@ impl Precise for Decimal256 {
fn round(&self, p: &Precision) -> Self {
match p {
Precision::SignificantFigures(sf) => {
// early return for zero significant figures
if sf == &0 {
return Self::zero();
}
let int = self.numerator();
let len = int.to_string().as_str().bytes().len() as u32;
let decimals: u32 = len - *sf as u32;
let pow = Uint256::from(10u128).pow(decimals);
let truncated = Self::from_ratio(int, pow) * Uint256::from(1u128);
Self::from_ratio(truncated * pow, self.denominator())
let figures = int.to_string().len() as u32;
let pow = Uint256::from(10u128).pow(figures - *sf as u32);
let significant_part = int / pow; // integer division truncates
let truncated = significant_part * pow;
Self::new(truncated)
}
Precision::DecimalPlaces(dp) => {
let pow = Uint256::from(10u128).pow(18 - *dp as u32);
let x = Self::from_ratio(self.numerator(), self.denominator() * pow);
Self::from_ratio(x.numerator() * pow, x.denominator())
let significant_part = self.numerator() / pow; // integer division truncates
Self::new(significant_part * pow)
}
}
}
Expand Down Expand Up @@ -92,4 +100,60 @@ mod tests {
assert_eq!(p.validate(&Decimal::from_str("12.343").unwrap()), None);
assert_eq!(p.validate(&Decimal::from_str("1.2").unwrap()), Some(()));
}

#[test]
fn test_significant_figures_round() {
const CASES: [(u8, &str, &str); 7] = [
(2, "123.456", "120"),
(4, "12.345678910111213141", "12.34"),
(18, "0.123456789101213141", "0.123456789101213141"),
(2, "0.123456", "0.12"),
(18 + 3, "123.456", "123.456"),
(0, "123.456", "0"),
(1, "123", "100"),
];

for (precision, unrounded, expected) in CASES {
let p = Precision::SignificantFigures(precision);
assert_eq!(
Decimal::from_str(unrounded).unwrap().round(&p),
Decimal::from_str(expected).unwrap()
);
assert_eq!(
Decimal256::from_str(unrounded).unwrap().round(&p),
Decimal256::from_str(expected).unwrap()
);
}
}

#[test]
#[should_panic]
fn test_significant_figures_round_panic() {
let p = Precision::SignificantFigures(18 + 4);
_ = Decimal::from_str("123.456").unwrap().round(&p);
}

#[test]
fn test_decimal_places_round() {
const CASES: [(u8, &str, &str); 6] = [
(2, "123.456", "123.45"),
(4, "12.345678910111213141", "12.3456"),
(18, "0.123456789101213141", "0.123456789101213141"),
(2, "0.123456", "0.12"),
(0, "123.456", "123"),
(1, "123", "123"),
];

for (precision, unrounded, expected) in CASES {
let p = Precision::DecimalPlaces(precision);
assert_eq!(
Decimal::from_str(unrounded).unwrap().round(&p),
Decimal::from_str(expected).unwrap()
);
assert_eq!(
Decimal256::from_str(unrounded).unwrap().round(&p),
Decimal256::from_str(expected).unwrap()
);
}
}
}