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use super::mul_rem::MulRem;
pub trait CheckedPowRemEuclid<Exponent, Divisor> {
type Output;
/// Returns remainder of checked power's euclidean division.
/// ```
/// use traiter::numbers::CheckedPowRemEuclid;
/// // signed integers
/// assert_eq!(
/// CheckedPowRemEuclid::checked_pow_rem_euclid(-3i8, 0u32, 2i8),
/// Some(1i8)
/// );
/// assert_eq!(
/// CheckedPowRemEuclid::checked_pow_rem_euclid(-3i8, 1u32, 1i8),
/// Some(0i8)
/// );
/// assert_eq!(
/// CheckedPowRemEuclid::checked_pow_rem_euclid(-3i8, 2u32, 0i8),
/// None
/// );
/// assert_eq!(
/// CheckedPowRemEuclid::checked_pow_rem_euclid(i8::MIN, 1u32, -1i8),
/// None
/// );
/// // unsigned integers
/// assert_eq!(
/// CheckedPowRemEuclid::checked_pow_rem_euclid(3u8, 0u32, 2u8),
/// Some(1u8)
/// );
/// assert_eq!(
/// CheckedPowRemEuclid::checked_pow_rem_euclid(3u8, 1u32, 1u8),
/// Some(0u8)
/// );
/// assert_eq!(
/// CheckedPowRemEuclid::checked_pow_rem_euclid(3u8, 2u32, 0u8),
/// None
/// );
/// ```
fn checked_pow_rem_euclid(
self,
exponent: Exponent,
divisor: Divisor,
) -> Self::Output;
}
macro_rules! signed_integer_checked_pow_rem_euclid_impl {
($($integer:ty)*) => ($(
impl CheckedPowRemEuclid<u32, $integer> for $integer {
type Output = Option<$integer>;
#[inline]
fn checked_pow_rem_euclid(
self,
exponent: u32,
divisor: Self,
) -> Self::Output {
let base = if self < 0 || self > divisor {
self.checked_rem_euclid(divisor)?
} else {
self
};
if divisor == 1 || divisor == -1 {
return Some(0);
}
let mut result = base;
let mut exponent_mask = if exponent == 0u32 {
0u32
} else {
(1u32 << exponent.ilog2()) >> 1u32
};
while exponent_mask != 0 {
result = result.mul_rem(result, divisor);
if exponent & exponent_mask != 0 {
result = result.mul_rem(base, divisor);
}
exponent_mask >>= 1;
}
Some(result)
}
}
)*)
}
signed_integer_checked_pow_rem_euclid_impl!(i8 i16 i32 i64 i128 isize);
macro_rules! unsigned_integer_checked_pow_rem_euclid_impl {
($($integer:ty)*) => ($(
impl CheckedPowRemEuclid<u32, Self> for $integer {
type Output = Option<Self>;
#[inline]
fn checked_pow_rem_euclid(
self,
exponent: u32,
divisor: Self,
) -> Self::Output {
if divisor == 0 {
None
} else if divisor == 1 {
Some(0)
} else {
let base = if self > divisor {
unsafe {
self.checked_rem_euclid(divisor).unwrap_unchecked()
}
} else {
self
};
let mut result = base;
let mut exponent_mask = 2u32;
loop {
if exponent_mask > exponent {
exponent_mask >>= 1;
break;
}
exponent_mask <<= 1;
}
exponent_mask >>= 1;
while exponent_mask != 0 {
result = result.mul_rem(result, divisor);
if exponent & exponent_mask != 0 {
result = result.mul_rem(base, divisor);
}
exponent_mask >>= 1;
}
Some(result)
}
}
}
)*)
}
unsigned_integer_checked_pow_rem_euclid_impl!(u8 u16 u32 u64 u128 usize);