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Make Int % Uint return a Uint #892

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83 changes: 37 additions & 46 deletions src/int/div_uint.rs
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Original file line number Diff line number Diff line change
@@ -1,14 +1,14 @@
//! Operations related to dividing an [`Int`] by a [`Uint`].
use core::ops::{Div, DivAssign, Rem, RemAssign};
use core::ops::{Div, DivAssign, Rem};

use crate::{ConstChoice, Int, NonZero, Uint, Wrapping};

/// Checked division operations.
impl<const LIMBS: usize> Int<LIMBS> {
#[inline]
/// Base div_rem operation on dividing an [`Int`] by a [`Uint`].
/// Computes the quotient and remainder of `self / rhs`.
/// Furthermore, returns the sign of `self`.
#[inline]
const fn div_rem_base_uint<const RHS_LIMBS: usize>(
&self,
rhs: &NonZero<Uint<RHS_LIMBS>>,
Expand All @@ -25,21 +25,21 @@ impl<const LIMBS: usize> Int<LIMBS> {
/// use crypto_bigint::{I128, NonZero, U128};
///
/// let (quotient, remainder) = I128::from(8).div_rem_uint(&U128::from(3u32).to_nz().unwrap());
/// assert_eq!(quotient, I128::from(2));
/// assert_eq!(remainder, I128::from(2));
/// assert_eq!(quotient, I128::from(2i32));
/// assert_eq!(remainder, U128::from(2u32));
///
/// let (quotient, remainder) = I128::from(-8).div_rem_uint(&U128::from(3u32).to_nz().unwrap());
/// assert_eq!(quotient, I128::from(-2));
/// assert_eq!(remainder, I128::from(-2));
/// assert_eq!(quotient, I128::from(-2i32));
/// assert_eq!(remainder, U128::from(1u32));
/// ```
pub const fn div_rem_uint<const RHS_LIMBS: usize>(
&self,
rhs: &NonZero<Uint<RHS_LIMBS>>,
) -> (Self, Int<RHS_LIMBS>) {
) -> (Self, Uint<RHS_LIMBS>) {
let (quotient, remainder, lhs_sgn) = self.div_rem_base_uint(rhs);
(
Self(quotient).wrapping_neg_if(lhs_sgn),
Int::new_from_abs_sign(remainder, lhs_sgn).expect("no overflow; always fits"),
Uint::select(&remainder, &rhs.0.wrapping_sub(&remainder), lhs_sgn),
)
}

Expand All @@ -54,20 +54,20 @@ impl<const LIMBS: usize> Int<LIMBS> {
pub const fn rem_uint<const RHS_LIMBS: usize>(
&self,
rhs: &NonZero<Uint<RHS_LIMBS>>,
) -> Int<RHS_LIMBS> {
) -> Uint<RHS_LIMBS> {
self.div_rem_uint(rhs).1
}
}

/// Vartime checked division operations.
impl<const LIMBS: usize> Int<LIMBS> {
#[inline]
/// Variable time equivalent of [`Self::div_rem_base_uint`].
///
/// This is variable only with respect to `rhs`.
///
/// When used with a fixed `rhs`, this function is constant-time with respect
/// to `self`.
#[inline]
const fn div_rem_base_uint_vartime<const RHS_LIMBS: usize>(
&self,
rhs: &NonZero<Uint<RHS_LIMBS>>,
Expand All @@ -86,11 +86,11 @@ impl<const LIMBS: usize> Int<LIMBS> {
pub const fn div_rem_uint_vartime<const RHS_LIMBS: usize>(
&self,
rhs: &NonZero<Uint<RHS_LIMBS>>,
) -> (Self, Int<RHS_LIMBS>) {
) -> (Self, Uint<RHS_LIMBS>) {
let (quotient, remainder, lhs_sgn) = self.div_rem_base_uint_vartime(rhs);
(
Self(quotient).wrapping_neg_if(lhs_sgn),
remainder.as_int().wrapping_neg_if(lhs_sgn),
Uint::select(&remainder, &rhs.0.wrapping_sub(&remainder), lhs_sgn),
)
}

Expand All @@ -116,7 +116,7 @@ impl<const LIMBS: usize> Int<LIMBS> {
pub const fn rem_uint_vartime<const RHS_LIMBS: usize>(
&self,
rhs: &NonZero<Uint<RHS_LIMBS>>,
) -> Int<RHS_LIMBS> {
) -> Uint<RHS_LIMBS> {
self.div_rem_uint_vartime(rhs).1
}
}
Expand Down Expand Up @@ -356,53 +356,41 @@ impl<const LIMBS: usize> DivAssign<NonZero<Uint<LIMBS>>> for Wrapping<Int<LIMBS>
}

impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<&NonZero<Uint<RHS_LIMBS>>> for &Int<LIMBS> {
type Output = Int<RHS_LIMBS>;
type Output = Uint<RHS_LIMBS>;

fn rem(self, rhs: &NonZero<Uint<RHS_LIMBS>>) -> Self::Output {
*self % *rhs
}
}

impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<&NonZero<Uint<RHS_LIMBS>>> for Int<LIMBS> {
type Output = Int<RHS_LIMBS>;
type Output = Uint<RHS_LIMBS>;

fn rem(self, rhs: &NonZero<Uint<RHS_LIMBS>>) -> Self::Output {
self % *rhs
}
}

impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<NonZero<Uint<RHS_LIMBS>>> for &Int<LIMBS> {
type Output = Int<RHS_LIMBS>;
type Output = Uint<RHS_LIMBS>;

fn rem(self, rhs: NonZero<Uint<RHS_LIMBS>>) -> Self::Output {
*self % rhs
}
}

impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<NonZero<Uint<RHS_LIMBS>>> for Int<LIMBS> {
type Output = Int<RHS_LIMBS>;
type Output = Uint<RHS_LIMBS>;

fn rem(self, rhs: NonZero<Uint<RHS_LIMBS>>) -> Self::Output {
Self::rem_uint(&self, &rhs)
}
}

impl<const LIMBS: usize> RemAssign<&NonZero<Uint<LIMBS>>> for Int<LIMBS> {
fn rem_assign(&mut self, rhs: &NonZero<Uint<LIMBS>>) {
*self %= *rhs
}
}

impl<const LIMBS: usize> RemAssign<NonZero<Uint<LIMBS>>> for Int<LIMBS> {
fn rem_assign(&mut self, rhs: NonZero<Uint<LIMBS>>) {
*self = *self % rhs;
}
}

impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<NonZero<Uint<RHS_LIMBS>>>
for Wrapping<Int<LIMBS>>
{
type Output = Wrapping<Int<RHS_LIMBS>>;
type Output = Wrapping<Uint<RHS_LIMBS>>;

fn rem(self, rhs: NonZero<Uint<RHS_LIMBS>>) -> Self::Output {
Wrapping(self.0 % rhs)
Expand All @@ -412,7 +400,7 @@ impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<NonZero<Uint<RHS_LIMBS>>>
impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<NonZero<Uint<RHS_LIMBS>>>
for &Wrapping<Int<LIMBS>>
{
type Output = Wrapping<Int<RHS_LIMBS>>;
type Output = Wrapping<Uint<RHS_LIMBS>>;

fn rem(self, rhs: NonZero<Uint<RHS_LIMBS>>) -> Self::Output {
*self % rhs
Expand All @@ -422,7 +410,7 @@ impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<NonZero<Uint<RHS_LIMBS>>>
impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<&NonZero<Uint<RHS_LIMBS>>>
for &Wrapping<Int<LIMBS>>
{
type Output = Wrapping<Int<RHS_LIMBS>>;
type Output = Wrapping<Uint<RHS_LIMBS>>;

fn rem(self, rhs: &NonZero<Uint<RHS_LIMBS>>) -> Self::Output {
*self % *rhs
Expand All @@ -432,25 +420,13 @@ impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<&NonZero<Uint<RHS_LIMBS>>>
impl<const LIMBS: usize, const RHS_LIMBS: usize> Rem<&NonZero<Uint<RHS_LIMBS>>>
for Wrapping<Int<LIMBS>>
{
type Output = Wrapping<Int<RHS_LIMBS>>;
type Output = Wrapping<Uint<RHS_LIMBS>>;

fn rem(self, rhs: &NonZero<Uint<RHS_LIMBS>>) -> Self::Output {
self % *rhs
}
}

impl<const LIMBS: usize> RemAssign<NonZero<Uint<LIMBS>>> for Wrapping<Int<LIMBS>> {
fn rem_assign(&mut self, rhs: NonZero<Uint<LIMBS>>) {
*self %= &rhs;
}
}

impl<const LIMBS: usize> RemAssign<&NonZero<Uint<LIMBS>>> for Wrapping<Int<LIMBS>> {
fn rem_assign(&mut self, rhs: &NonZero<Uint<LIMBS>>) {
*self = Wrapping(self.0 % rhs)
}
}

#[cfg(test)]
mod tests {
#[cfg(feature = "rand_core")]
Expand All @@ -460,7 +436,7 @@ mod tests {
rand_core::SeedableRng,
};

use crate::{I128, U128};
use crate::{I128, I256, U128};

#[test]
fn test_div_uint() {
Expand Down Expand Up @@ -556,6 +532,21 @@ mod tests {
);
}

#[test]
fn test_rem_uint() {
let num =
I256::from_be_hex("eed8f6c7a5b1a65031ebc9b7a93492e89f282d49e75d25607a5693b3d8ae2e87");
let denom = U128::from_be_hex("de157f812521c55eccf9a903b31e4a34")
.to_nz()
.unwrap();
let expect = U128::from_be_hex("44bfe3176459710d0d0848f99b37e47b");
assert_eq!(num.rem_uint(&denom), expect);
assert_eq!(
num.wrapping_neg().rem_uint(&denom),
denom.wrapping_sub(&expect)
);
}

#[cfg(feature = "rand_core")]
#[test]
fn test_div_floor_ct_vs_vt() {
Expand Down