Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Decimal checked multiplication and exponentiation #1239

Merged
merged 5 commits into from
Mar 10, 2022
Merged

Decimal checked multiplication and exponentiation #1239

Show file tree
Hide file tree
Changes from 3 commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
56bc979
cosmwasm_std: Decimal checked multiplication
uint Mar 10, 2022
16a21b5
cosmwasm_std: Decimal checked_pow
uint Mar 10, 2022
088171b
document checked mul and pow for decimal types
uint Mar 10, 2022
4fa4d6e
Decimal::checked_pow 0^0 = 1 test
uint Mar 10, 2022
bbadca5
more comments
uint Mar 10, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 2 additions & 0 deletions CHANGELOG.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@ and this project adheres to
### Added

- cosmwasm-std: Implement `ops::Rem` for `Uint{64,128,256,512}`.
- cosmwasm-std: Implement `Decimal{,256}::checked_mul` and
`Decimal{,256}::checked_pow`.

### Changed

Expand Down
162 changes: 162 additions & 0 deletions packages/std/src/math/decimal.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ use std::str::FromStr;
use thiserror::Error;

use crate::errors::StdError;
use crate::OverflowError;

use super::Fraction;
use super::Isqrt;
Expand Down Expand Up @@ -151,6 +152,53 @@ impl Decimal {
Self::DECIMAL_PLACES as u32
}

/// Multiplies one `Decimal` by another, returning an `OverflowError` if an overflow occurred.
pub fn checked_mul(self, other: Self) -> Result<Self, OverflowError> {
let result_as_uint256 = self.numerator().full_mul(other.numerator())
/ Uint256::from_uint128(Self::DECIMAL_FRACTIONAL); // from_uint128 is a const method and should be "free"
result_as_uint256
.try_into()
.map(Self)
.map_err(|_| OverflowError {
operation: crate::OverflowOperation::Mul,
operand1: self.to_string(),
operand2: other.to_string(),
})
}

/// Raises a value to the power of `exp`, returning an `OverflowError` if an overflow occurred.
pub fn checked_pow(self, exp: u32) -> Result<Self, OverflowError> {
// This uses the exponentiation by squaring algorithm:
// https://en.wikipedia.org/wiki/Exponentiation_by_squaring#Basic_method

fn inner(mut x: Decimal, mut n: u32) -> Result<Decimal, OverflowError> {
if n == 0 {
return Ok(Decimal::one());
}

let mut y = Decimal::one();

while n > 1 {
if n % 2 == 0 {
x = x.checked_mul(x)?;
n /= 2;
} else {
y = x.checked_mul(y)?;
x = x.checked_mul(x)?;
n = (n - 1) / 2;
}
}

Ok(x * y)
}

inner(self, exp).map_err(|_| OverflowError {
operation: crate::OverflowOperation::Pow,
operand1: self.to_string(),
operand2: exp.to_string(),
})
}

/// Returns the approximate square root as a Decimal.
///
/// This should not overflow or panic.
Expand Down Expand Up @@ -952,6 +1000,37 @@ mod tests {
let _value = Decimal::MAX * Decimal::percent(101);
}

#[test]
fn decimal_checked_mul() {
let test_data = [
(Decimal::zero(), Decimal::zero()),
(Decimal::zero(), Decimal::one()),
(Decimal::one(), Decimal::zero()),
(Decimal::percent(10), Decimal::zero()),
(Decimal::percent(10), Decimal::percent(5)),
(Decimal::MAX, Decimal::one()),
(Decimal::MAX / 2u128.into(), Decimal::percent(200)),
(Decimal::permille(6), Decimal::permille(13)),
];

// The regular std::ops::Mul is our source of truth for these tests.
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Nice

for (x, y) in test_data.iter().cloned() {
assert_eq!(x * y, x.checked_mul(y).unwrap());
}
}

#[test]
fn decimal_checked_mul_overflow() {
assert_eq!(
Decimal::MAX.checked_mul(Decimal::percent(200)),
Err(OverflowError {
operation: crate::OverflowOperation::Mul,
operand1: Decimal::MAX.to_string(),
operand2: Decimal::percent(200).to_string(),
})
);
}

#[test]
// in this test the Decimal is on the right
fn uint128_decimal_multiply() {
Expand Down Expand Up @@ -1068,6 +1147,89 @@ mod tests {
);
}

#[test]
fn decimal_checked_pow() {
for exp in 0..10 {
assert_eq!(Decimal::one().checked_pow(exp).unwrap(), Decimal::one());
}

// Do we leave 0^0 undefined?
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

What about going with the Rust standard library behaviour of expecting 1 in the implementation, even though this is mathematically undefined.

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=20df6716048e77087acd40194b233494

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Makes sense! Done.


for exp in 1..10 {
assert_eq!(Decimal::zero().checked_pow(exp).unwrap(), Decimal::zero());
}

for num in &[
Decimal::percent(50),
Decimal::percent(99),
Decimal::percent(200),
] {
assert_eq!(num.checked_pow(0).unwrap(), Decimal::one())
}

assert_eq!(
Decimal::percent(20).checked_pow(2).unwrap(),
Decimal::percent(4)
);

assert_eq!(
Decimal::percent(20).checked_pow(3).unwrap(),
Decimal::permille(8)
);

assert_eq!(
Decimal::percent(200).checked_pow(4).unwrap(),
Decimal::percent(1600)
);

assert_eq!(
Decimal::percent(200).checked_pow(4).unwrap(),
Decimal::percent(1600)
);

assert_eq!(
Decimal::percent(700).checked_pow(5).unwrap(),
Decimal::percent(1680700)
);

assert_eq!(
Decimal::percent(700).checked_pow(8).unwrap(),
Decimal::percent(576480100)
);

assert_eq!(
Decimal::percent(700).checked_pow(10).unwrap(),
Decimal::percent(28247524900)
);

assert_eq!(
Decimal::percent(120).checked_pow(123).unwrap(),
Decimal(5486473221892422150877397607u128.into())
);

assert_eq!(
Decimal::percent(10).checked_pow(2).unwrap(),
Decimal(10000000000000000u128.into())
);

assert_eq!(
Decimal::percent(10).checked_pow(18).unwrap(),
Decimal(1u128.into())
);
}

#[test]
fn decimal_checked_pow_overflow() {
assert_eq!(
Decimal::MAX.checked_pow(2),
Err(OverflowError {
operation: crate::OverflowOperation::Pow,
operand1: Decimal::MAX.to_string(),
operand2: "2".to_string(),
})
);
}

#[test]
fn decimal_to_string() {
// Integers
Expand Down
169 changes: 168 additions & 1 deletion packages/std/src/math/decimal256.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ use std::str::FromStr;
use thiserror::Error;

use crate::errors::StdError;
use crate::Uint512;
use crate::{OverflowError, Uint512};

use super::Fraction;
use super::Isqrt;
Expand Down Expand Up @@ -164,6 +164,53 @@ impl Decimal256 {
Self::DECIMAL_PLACES as u32
}

/// Multiplies one `Decimal256` by another, returning an `OverflowError` if an overflow occurred.
pub fn checked_mul(self, other: Self) -> Result<Self, OverflowError> {
let result_as_uint512 = self.numerator().full_mul(other.numerator())
/ Uint512::from_uint256(Self::DECIMAL_FRACTIONAL); // from_uint128 is a const method and should be "free"
result_as_uint512
.try_into()
.map(Self)
.map_err(|_| OverflowError {
operation: crate::OverflowOperation::Mul,
operand1: self.to_string(),
operand2: other.to_string(),
})
}

/// Raises a value to the power of `exp`, returning an `OverflowError` if an overflow occurred.
pub fn checked_pow(self, exp: u32) -> Result<Self, OverflowError> {
// This uses the exponentiation by squaring algorithm:
// https://en.wikipedia.org/wiki/Exponentiation_by_squaring#Basic_method

fn inner(mut x: Decimal256, mut n: u32) -> Result<Decimal256, OverflowError> {
if n == 0 {
return Ok(Decimal256::one());
}

let mut y = Decimal256::one();

while n > 1 {
if n % 2 == 0 {
x = x.checked_mul(x)?;
n /= 2;
} else {
y = x.checked_mul(y)?;
x = x.checked_mul(x)?;
n = (n - 1) / 2;
}
}

Ok(x * y)
}

inner(self, exp).map_err(|_| OverflowError {
operation: crate::OverflowOperation::Pow,
operand1: self.to_string(),
operand2: exp.to_string(),
})
}

/// Returns the approximate square root as a Decimal256.
///
/// This should not overflow or panic.
Expand Down Expand Up @@ -1031,6 +1078,37 @@ mod tests {
let _value = Decimal256::MAX * Decimal256::percent(101);
}

#[test]
fn decimal256_checked_mul() {
let test_data = [
(Decimal256::zero(), Decimal256::zero()),
(Decimal256::zero(), Decimal256::one()),
(Decimal256::one(), Decimal256::zero()),
(Decimal256::percent(10), Decimal256::zero()),
(Decimal256::percent(10), Decimal256::percent(5)),
(Decimal256::MAX, Decimal256::one()),
(Decimal256::MAX / 2u128.into(), Decimal256::percent(200)),
(Decimal256::permille(6), Decimal256::permille(13)),
];

// The regular std::ops::Mul is our source of truth for these tests.
for (x, y) in test_data.iter().cloned() {
assert_eq!(x * y, x.checked_mul(y).unwrap());
}
}

#[test]
fn decimal256_checked_mul_overflow() {
assert_eq!(
Decimal256::MAX.checked_mul(Decimal256::percent(200)),
Err(OverflowError {
operation: crate::OverflowOperation::Mul,
operand1: Decimal256::MAX.to_string(),
operand2: Decimal256::percent(200).to_string(),
})
);
}

#[test]
// in this test the Decimal256 is on the right
fn uint128_decimal_multiply() {
Expand Down Expand Up @@ -1151,6 +1229,95 @@ mod tests {
);
}

#[test]
fn decimal256_checked_pow() {
for exp in 0..10 {
assert_eq!(
Decimal256::one().checked_pow(exp).unwrap(),
Decimal256::one()
);
}

// Do we leave 0^0 undefined?

for exp in 1..10 {
assert_eq!(
Decimal256::zero().checked_pow(exp).unwrap(),
Decimal256::zero()
);
}

for num in &[
Decimal256::percent(50),
Decimal256::percent(99),
Decimal256::percent(200),
] {
assert_eq!(num.checked_pow(0).unwrap(), Decimal256::one())
}

assert_eq!(
Decimal256::percent(20).checked_pow(2).unwrap(),
Decimal256::percent(4)
);

assert_eq!(
Decimal256::percent(20).checked_pow(3).unwrap(),
Decimal256::permille(8)
);

assert_eq!(
Decimal256::percent(200).checked_pow(4).unwrap(),
Decimal256::percent(1600)
);

assert_eq!(
Decimal256::percent(200).checked_pow(4).unwrap(),
Decimal256::percent(1600)
);

assert_eq!(
Decimal256::percent(700).checked_pow(5).unwrap(),
Decimal256::percent(1680700)
);

assert_eq!(
Decimal256::percent(700).checked_pow(8).unwrap(),
Decimal256::percent(576480100)
);

assert_eq!(
Decimal256::percent(700).checked_pow(10).unwrap(),
Decimal256::percent(28247524900)
);

assert_eq!(
Decimal256::percent(120).checked_pow(123).unwrap(),
Decimal256(5486473221892422150877397607u128.into())
);

assert_eq!(
Decimal256::percent(10).checked_pow(2).unwrap(),
Decimal256(10000000000000000u128.into())
);

assert_eq!(
Decimal256::percent(10).checked_pow(18).unwrap(),
Decimal256(1u128.into())
);
}

#[test]
fn decimal256_checked_pow_overflow() {
assert_eq!(
Decimal256::MAX.checked_pow(2),
Err(OverflowError {
operation: crate::OverflowOperation::Pow,
operand1: Decimal256::MAX.to_string(),
operand2: "2".to_string(),
})
);
}

#[test]
fn decimal256_to_string() {
// Integers
Expand Down