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//! Rounding operations for `Decimal`.
//!
//! All methods are `const fn`, generated per backing type via macro.
use crate::Decimal;
macro_rules! impl_decimal_rounding {
($backing:ty, $pow10_fn:path) => {
impl<const D: u8> Decimal<$backing, D> {
/// Rounds toward negative infinity.
///
/// # Examples
///
/// ```
/// use nexus_decimal::Decimal;
/// type D64 = Decimal<i64, 8>;
///
/// let pos = D64::new(1, 75_000_000); // 1.75
/// assert_eq!(pos.floor().to_raw(), D64::new(1, 0).to_raw());
///
/// let neg = D64::new(-1, 75_000_000); // -1.75
/// assert_eq!(neg.floor().to_raw(), D64::new(-2, 0).to_raw());
/// ```
#[inline(always)]
pub const fn floor(self) -> Self {
let remainder = self.value % Self::SCALE;
if remainder >= 0 {
Self {
value: self.value - remainder,
}
} else {
// self.value - remainder gives next integer toward zero.
// Subtract SCALE to go one step negative. Saturate on underflow.
let toward_zero = self.value - remainder;
match toward_zero.checked_sub(Self::SCALE) {
Some(v) => Self { value: v },
None => Self::MIN,
}
}
}
/// Rounds toward positive infinity.
///
/// # Examples
///
/// ```
/// use nexus_decimal::Decimal;
/// type D64 = Decimal<i64, 8>;
///
/// let pos = D64::new(1, 25_000_000); // 1.25
/// assert_eq!(pos.ceil().to_raw(), D64::new(2, 0).to_raw());
///
/// let neg = D64::new(-1, 25_000_000); // -1.25
/// assert_eq!(neg.ceil().to_raw(), D64::new(-1, 0).to_raw());
/// ```
#[inline(always)]
pub const fn ceil(self) -> Self {
let remainder = self.value % Self::SCALE;
if remainder > 0 {
let toward_zero = self.value - remainder;
match toward_zero.checked_add(Self::SCALE) {
Some(v) => Self { value: v },
None => Self::MAX,
}
} else {
Self {
value: self.value - remainder,
}
}
}
/// Truncates toward zero (removes fractional part).
///
/// # Examples
///
/// ```
/// use nexus_decimal::Decimal;
/// type D64 = Decimal<i64, 8>;
///
/// let pos = D64::new(1, 99_000_000); // 1.99
/// assert_eq!(pos.trunc().to_raw(), D64::new(1, 0).to_raw());
///
/// let neg = D64::new(-1, 99_000_000); // -1.99
/// assert_eq!(neg.trunc().to_raw(), D64::new(-1, 0).to_raw());
/// ```
#[inline(always)]
pub const fn trunc(self) -> Self {
Self {
value: (self.value / Self::SCALE) * Self::SCALE,
}
}
/// Returns the fractional part (same sign as `self`).
///
/// Invariant: `self == self.trunc() + self.fract()`.
#[inline(always)]
pub const fn fract(self) -> Self {
Self {
value: self.value % Self::SCALE,
}
}
/// Returns the integer part as the backing type.
///
/// Equivalent to `self.trunc().to_raw() / SCALE`.
#[inline(always)]
pub const fn to_integer(self) -> $backing {
self.value / Self::SCALE
}
/// Rounds to the nearest integer using banker's rounding
/// (round half to even).
///
/// # Examples
///
/// ```
/// use nexus_decimal::Decimal;
/// type D64 = Decimal<i64, 8>;
///
/// // Half rounds to even
/// let half_even = D64::new(2, 50_000_000); // 2.5
/// assert_eq!(half_even.round().to_raw(), D64::new(2, 0).to_raw());
///
/// let half_odd = D64::new(3, 50_000_000); // 3.5
/// assert_eq!(half_odd.round().to_raw(), D64::new(4, 0).to_raw());
/// ```
#[inline(always)]
pub const fn round(self) -> Self {
let quotient = self.value / Self::SCALE;
let remainder = self.value % Self::SCALE;
let half = Self::SCALE / 2;
let rounded = if remainder > half {
quotient + 1
} else if remainder < -half {
quotient - 1
} else if remainder == half {
// Banker's rounding: round to even
if quotient & 1 != 0 {
quotient + 1
} else {
quotient
}
} else if remainder == -half {
if quotient & 1 != 0 {
quotient - 1
} else {
quotient
}
} else {
quotient
};
match rounded.checked_mul(Self::SCALE) {
Some(v) => Self { value: v },
None => {
if rounded > 0 {
Self::MAX
} else {
Self::MIN
}
}
}
}
/// Rounds to `dp` decimal places using banker's rounding.
///
/// # Panics
///
/// Panics if `dp >= DECIMALS`.
///
/// # Examples
///
/// ```
/// use nexus_decimal::Decimal;
/// type D64 = Decimal<i64, 8>;
///
/// let price = D64::new(1, 23_456_789); // 1.23456789
/// let rounded = price.round_dp(2); // 1.23
/// assert_eq!(rounded.to_raw(), D64::new(1, 23_000_000).to_raw());
/// ```
#[inline]
pub const fn round_dp(self, dp: u8) -> Self {
assert!(dp < D, "round_dp: dp must be less than DECIMALS");
let sub_scale = $pow10_fn(D - dp);
let half = sub_scale / 2;
let quotient = self.value / sub_scale;
let remainder = self.value % sub_scale;
let rounded = if remainder > half {
quotient + 1
} else if remainder < -half {
quotient - 1
} else if remainder == half {
if quotient & 1 != 0 {
quotient + 1
} else {
quotient
}
} else if remainder == -half {
if quotient & 1 != 0 {
quotient - 1
} else {
quotient
}
} else {
quotient
};
match rounded.checked_mul(sub_scale) {
Some(v) => Self { value: v },
None => {
if rounded > 0 {
Self::MAX
} else {
Self::MIN
}
}
}
}
}
};
}
use crate::pow10::{pow10_i32, pow10_i64, pow10_i128};
impl_decimal_rounding!(i32, pow10_i32);
impl_decimal_rounding!(i64, pow10_i64);
impl_decimal_rounding!(i128, pow10_i128);