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use crate::num::arithmetic::traits::{ModPowerOf2Mul, ModPowerOf2MulAssign};
use crate::num::basic::unsigneds::PrimitiveUnsigned;
fn mod_power_of_2_mul<T: PrimitiveUnsigned>(x: T, y: T, pow: u64) -> T {
assert!(pow <= T::WIDTH);
assert!(
x.significant_bits() <= pow,
"x must be reduced mod 2^pow, but {x} >= 2^{pow}"
);
assert!(
y.significant_bits() <= pow,
"y must be reduced mod 2^pow, but {y} >= 2^{pow}"
);
x.wrapping_mul(y).mod_power_of_2(pow)
}
#[inline]
fn mod_power_of_2_mul_assign<T: PrimitiveUnsigned>(x: &mut T, y: T, pow: u64) {
assert!(pow <= T::WIDTH);
assert!(
x.significant_bits() <= pow,
"x must be reduced mod 2^pow, but {x} >= 2^{pow}"
);
assert!(
y.significant_bits() <= pow,
"y must be reduced mod 2^pow, but {y} >= 2^{pow}"
);
x.wrapping_mul_assign(y);
x.mod_power_of_2_assign(pow);
}
macro_rules! impl_mod_power_of_2_mul {
($t:ident) => {
impl ModPowerOf2Mul<$t> for $t {
type Output = $t;
/// Multiplies two numbers modulo a third number $2^k$. The inputs must be already
/// reduced modulo $2^k$.
///
/// $f(x, y, k) = z$, where $x, y, z < 2^k$ and $xy \equiv z \mod 2^k$.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Panics
/// Panics if `pow` is greater than `Self::WIDTH` or if `self` or `other` are greater
/// than or equal to $2^k$.
///
/// # Examples
/// See [here](super::mod_power_of_2_mul#mod_power_of_2_mul).
#[inline]
fn mod_power_of_2_mul(self, other: $t, pow: u64) -> $t {
mod_power_of_2_mul(self, other, pow)
}
}
impl ModPowerOf2MulAssign<$t> for $t {
/// Multiplies two numbers modulo a third number $2^k$, in place. The inputs must be
/// already reduced modulo $2^k$.
///
/// $x \gets z$, where $x, y, z < 2^k$ and $xy \equiv z \mod 2^k$.
///
/// # Worst-case complexity
/// Constant time and additional memory.
///
/// # Panics
/// Panics if `pow` is greater than `Self::WIDTH` or if `self` or `other` are greater
/// than or equal to $2^k$.
///
/// # Examples
/// See [here](super::mod_power_of_2_mul#mod_power_of_2_mul_assign).
#[inline]
fn mod_power_of_2_mul_assign(&mut self, other: $t, pow: u64) {
mod_power_of_2_mul_assign(self, other, pow)
}
}
};
}
apply_to_unsigneds!(impl_mod_power_of_2_mul);