149 lines
3.3 KiB
Rust
149 lines
3.3 KiB
Rust
use core::ops::Mul;
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use {One, CheckedMul};
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/// Binary operator for raising a value to a power.
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pub trait Pow<RHS> {
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/// The result after applying the operator.
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type Output;
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/// Returns `self` to the power `rhs`.
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///
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/// # Examples
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///
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/// ```
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/// use num_traits::Pow;
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/// assert_eq!(Pow::pow(10u32, 2u32), 100);
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/// ```
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fn pow(self, rhs: RHS) -> Self::Output;
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}
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macro_rules! pow_impl {
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($t:ty, $rhs:ty, $method:ident) => {
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impl Pow<$rhs> for $t {
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type Output = $t;
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#[inline]
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fn pow(self, rhs: $rhs) -> $t {
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<$t>::$method(self, rhs)
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}
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}
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impl<'a> Pow<&'a $rhs> for $t {
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type Output = $t;
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#[inline]
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fn pow(self, rhs: &'a $rhs) -> $t {
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<$t>::$method(self, *rhs)
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}
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}
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impl<'a> Pow<$rhs> for &'a $t {
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type Output = $t;
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#[inline]
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fn pow(self, rhs: $rhs) -> $t {
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<$t>::$method(*self, rhs)
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}
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}
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impl<'a, 'b> Pow<&'a $rhs> for &'b $t {
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type Output = $t;
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#[inline]
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fn pow(self, rhs: &'a $rhs) -> $t {
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<$t>::$method(*self, *rhs)
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}
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}
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}
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}
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pow_impl!(u8, u32, pow);
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pow_impl!(i8, u32, pow);
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pow_impl!(u16, u32, pow);
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pow_impl!(i16, u32, pow);
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pow_impl!(u32, u32, pow);
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pow_impl!(i32, u32, pow);
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pow_impl!(u64, u32, pow);
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pow_impl!(i64, u32, pow);
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pow_impl!(usize, u32, pow);
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pow_impl!(isize, u32, pow);
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#[cfg(feature = "std")]
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mod float_impls {
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use super::Pow;
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pow_impl!(f32, i32, powi);
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pow_impl!(f64, i32, powi);
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pow_impl!(f32, f32, powf);
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pow_impl!(f64, f64, powf);
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}
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/// Raises a value to the power of exp, using exponentiation by squaring.
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///
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/// # Example
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///
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/// ```rust
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/// use num_traits::pow;
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///
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/// assert_eq!(pow(2i8, 4), 16);
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/// assert_eq!(pow(6u8, 3), 216);
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/// ```
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#[inline]
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pub fn pow<T: Clone + One + Mul<T, Output = T>>(mut base: T, mut exp: usize) -> T {
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if exp == 0 { return T::one() }
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while exp & 1 == 0 {
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base = base.clone() * base;
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exp >>= 1;
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}
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if exp == 1 { return base }
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let mut acc = base.clone();
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while exp > 1 {
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exp >>= 1;
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base = base.clone() * base;
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if exp & 1 == 1 {
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acc = acc * base.clone();
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}
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}
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acc
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}
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/// Raises a value to the power of exp, returning `None` if an overflow occurred.
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///
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/// Otherwise same as the `pow` function.
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///
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/// # Example
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///
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/// ```rust
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/// use num_traits::checked_pow;
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///
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/// assert_eq!(checked_pow(2i8, 4), Some(16));
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/// assert_eq!(checked_pow(7i8, 8), None);
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/// assert_eq!(checked_pow(7u32, 8), Some(5_764_801));
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/// ```
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#[inline]
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pub fn checked_pow<T: Clone + One + CheckedMul>(mut base: T, mut exp: usize) -> Option<T> {
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if exp == 0 { return Some(T::one()) }
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macro_rules! optry {
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( $ expr : expr ) => {
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if let Some(val) = $expr { val } else { return None }
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}
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}
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while exp & 1 == 0 {
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base = optry!(base.checked_mul(&base));
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exp >>= 1;
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}
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if exp == 1 { return Some(base) }
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let mut acc = base.clone();
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while exp > 1 {
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exp >>= 1;
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base = optry!(base.checked_mul(&base));
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if exp & 1 == 1 {
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acc = optry!(acc.checked_mul(&base));
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}
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}
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Some(acc)
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}
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