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Generic exp for pow and checked_pow #300

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Generic exp for pow and checked_pow #300

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e128f9b
Generalize exp for pow and checked_pow
mtshr Nov 25, 2023
709c2ad
Use u32 for exp in FloatCore::powi
mtshr Nov 25, 2023
01c9c32
Implement Pow<u*> for primitive integers
mtshr Nov 25, 2023
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6 changes: 3 additions & 3 deletions src/float.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -700,10 +700,10 @@ pub trait FloatCore: Num + NumCast + Neg<Output = Self> + PartialOrd + Copy {
exp = exp.wrapping_neg();
self = self.recip();
}
// It should always be possible to convert a positive `i32` to a `usize`.
// It should always be possible to convert a positive `i32` to a `u32`.
// Note, `i32::MIN` will wrap and still be negative, so we need to convert
// to `u32` without sign-extension before growing to `usize`.
super::pow(self, (exp as u32).to_usize().unwrap())
// to `u32` without sign-extension.
super::pow(self, exp as u32)
}

/// Converts to degrees, assuming the number is in radians.
Expand Down
152 changes: 58 additions & 94 deletions src/pow.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
use crate::{CheckedMul, One};
use crate::{CheckedMul, One, PrimInt, Unsigned};
use core::num::Wrapping;
use core::ops::Mul;

/// Binary operator for raising a value to a power.
pub trait Pow<RHS> {
Expand All @@ -19,17 +18,24 @@ pub trait Pow<RHS> {
}

macro_rules! pow_impl {
(prim_int $t:ty) => {
pow_impl!($t, u8);
pow_impl!($t, u16);
pow_impl!($t, u32, u32, <$t>::pow);
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Utilizes the default implementation of pow for exp with u32

pow_impl!($t, u64);
pow_impl!($t, u128);
pow_impl!($t, usize);
};
($t:ty) => {
pow_impl!($t, u8);
pow_impl!($t, u16);
pow_impl!($t, u32);
pow_impl!($t, u64);
pow_impl!($t, u128);
pow_impl!($t, usize);

// FIXME: these should be possible
// pow_impl!($t, u16);
// pow_impl!($t, u32);
// pow_impl!($t, u64);
};
($t:ty, $rhs:ty) => {
pow_impl!($t, $rhs, usize, pow);
pow_impl!($t, $rhs, $rhs, pow);
};
($t:ty, $rhs:ty, $desired_rhs:ty, $method:expr) => {
impl Pow<$rhs> for $t {
Expand Down Expand Up @@ -66,57 +72,19 @@ macro_rules! pow_impl {
};
}

pow_impl!(u8, u8, u32, u8::pow);
pow_impl!(u8, u16, u32, u8::pow);
pow_impl!(u8, u32, u32, u8::pow);
pow_impl!(u8, usize);
pow_impl!(i8, u8, u32, i8::pow);
pow_impl!(i8, u16, u32, i8::pow);
pow_impl!(i8, u32, u32, i8::pow);
pow_impl!(i8, usize);
pow_impl!(u16, u8, u32, u16::pow);
pow_impl!(u16, u16, u32, u16::pow);
pow_impl!(u16, u32, u32, u16::pow);
pow_impl!(u16, usize);
pow_impl!(i16, u8, u32, i16::pow);
pow_impl!(i16, u16, u32, i16::pow);
pow_impl!(i16, u32, u32, i16::pow);
pow_impl!(i16, usize);
pow_impl!(u32, u8, u32, u32::pow);
pow_impl!(u32, u16, u32, u32::pow);
pow_impl!(u32, u32, u32, u32::pow);
pow_impl!(u32, usize);
pow_impl!(i32, u8, u32, i32::pow);
pow_impl!(i32, u16, u32, i32::pow);
pow_impl!(i32, u32, u32, i32::pow);
pow_impl!(i32, usize);
pow_impl!(u64, u8, u32, u64::pow);
pow_impl!(u64, u16, u32, u64::pow);
pow_impl!(u64, u32, u32, u64::pow);
pow_impl!(u64, usize);
pow_impl!(i64, u8, u32, i64::pow);
pow_impl!(i64, u16, u32, i64::pow);
pow_impl!(i64, u32, u32, i64::pow);
pow_impl!(i64, usize);

pow_impl!(u128, u8, u32, u128::pow);
pow_impl!(u128, u16, u32, u128::pow);
pow_impl!(u128, u32, u32, u128::pow);
pow_impl!(u128, usize);

pow_impl!(i128, u8, u32, i128::pow);
pow_impl!(i128, u16, u32, i128::pow);
pow_impl!(i128, u32, u32, i128::pow);
pow_impl!(i128, usize);

pow_impl!(usize, u8, u32, usize::pow);
pow_impl!(usize, u16, u32, usize::pow);
pow_impl!(usize, u32, u32, usize::pow);
pow_impl!(usize, usize);
pow_impl!(isize, u8, u32, isize::pow);
pow_impl!(isize, u16, u32, isize::pow);
pow_impl!(isize, u32, u32, isize::pow);
pow_impl!(isize, usize);
pow_impl!(prim_int u8);
pow_impl!(prim_int u16);
pow_impl!(prim_int u32);
pow_impl!(prim_int u64);
pow_impl!(prim_int u128);
pow_impl!(prim_int i8);
pow_impl!(prim_int i16);
pow_impl!(prim_int i32);
pow_impl!(prim_int i64);
pow_impl!(prim_int i128);
pow_impl!(prim_int usize);
pow_impl!(prim_int isize);

pow_impl!(Wrapping<u8>);
pow_impl!(Wrapping<i8>);
pow_impl!(Wrapping<u16>);
Expand All @@ -130,18 +98,6 @@ pow_impl!(Wrapping<i128>);
pow_impl!(Wrapping<usize>);
pow_impl!(Wrapping<isize>);

// FIXME: these should be possible
// pow_impl!(u8, u64);
// pow_impl!(i16, u64);
// pow_impl!(i8, u64);
// pow_impl!(u16, u64);
// pow_impl!(u32, u64);
// pow_impl!(i32, u64);
// pow_impl!(u64, u64);
// pow_impl!(i64, u64);
// pow_impl!(usize, u64);
// pow_impl!(isize, u64);

#[cfg(any(feature = "std", feature = "libm"))]
mod float_impls {
use super::Pow;
Expand Down Expand Up @@ -171,29 +127,33 @@ mod float_impls {
/// ```rust
/// use num_traits::pow;
///
/// assert_eq!(pow(2i8, 4), 16);
/// assert_eq!(pow(6u8, 3), 216);
/// assert_eq!(pow(0u8, 0), 1); // Be aware if this case affects you
/// assert_eq!(pow(2i8, 4u32), 16);
/// assert_eq!(pow(6u8, 3u32), 216);
/// assert_eq!(pow(0u8, 0u32), 1); // Be aware if this case affects you
/// ```
#[inline]
pub fn pow<T: Clone + One + Mul<T, Output = T>>(mut base: T, mut exp: usize) -> T {
if exp == 0 {
pub fn pow<T, U>(mut base: T, mut exp: U) -> T
where
T: Clone + One,
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I removed T: Mul<T, Output = T> because One needs it.

U: PrimInt + Unsigned,
{
if exp == U::zero() {
return T::one();
}

while exp & 1 == 0 {
while exp & U::one() == U::zero() {
base = base.clone() * base;
exp >>= 1;
exp = exp >> 1;
}
if exp == 1 {
if exp == U::one() {
return base;
}

let mut acc = base.clone();
while exp > 1 {
exp >>= 1;
while exp > U::one() {
exp = exp >> 1;
base = base.clone() * base;
if exp & 1 == 1 {
if exp & U::one() == U::one() {
acc = acc * base.clone();
}
}
Expand All @@ -211,30 +171,34 @@ pub fn pow<T: Clone + One + Mul<T, Output = T>>(mut base: T, mut exp: usize) ->
/// ```rust
/// use num_traits::checked_pow;
///
/// assert_eq!(checked_pow(2i8, 4), Some(16));
/// assert_eq!(checked_pow(7i8, 8), None);
/// assert_eq!(checked_pow(7u32, 8), Some(5_764_801));
/// assert_eq!(checked_pow(0u32, 0), Some(1)); // Be aware if this case affect you
/// assert_eq!(checked_pow(2i8, 4u32), Some(16));
/// assert_eq!(checked_pow(7i8, 8u32), None);
/// assert_eq!(checked_pow(7u32, 8u32), Some(5_764_801));
/// assert_eq!(checked_pow(0u32, 0u32), Some(1)); // Be aware if this case affect you
/// ```
#[inline]
pub fn checked_pow<T: Clone + One + CheckedMul>(mut base: T, mut exp: usize) -> Option<T> {
if exp == 0 {
pub fn checked_pow<T, U>(mut base: T, mut exp: U) -> Option<T>
where
T: Clone + One + CheckedMul,
U: PrimInt + Unsigned,
{
if exp == U::zero() {
return Some(T::one());
}

while exp & 1 == 0 {
while exp & U::one() == U::zero() {
base = base.checked_mul(&base)?;
exp >>= 1;
exp = exp >> 1;
}
if exp == 1 {
if exp == U::one() {
return Some(base);
}

let mut acc = base.clone();
while exp > 1 {
exp >>= 1;
while exp > U::one() {
exp = exp >> 1;
base = base.checked_mul(&base)?;
if exp & 1 == 1 {
if exp & U::one() == U::one() {
acc = acc.checked_mul(&base)?;
}
}
Expand Down