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Implement shift with broad RHS types #142

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merged 4 commits into from
Apr 4, 2020
Merged

Implement shift with broad RHS types #142

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bf8640e
Make the shift algorithms generic on PrimInt
cuviper Mar 20, 2020
cb1c2dd
Implement more shift RHS for BigUint
cuviper Mar 20, 2020
82b9d5c
Implement more shift RHS for BigInt
cuviper Mar 20, 2020
e827fd5
Reduce allocations in shift benchmarks
cuviper Mar 20, 2020
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10 changes: 6 additions & 4 deletions benches/bigint.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -293,9 +293,10 @@ fn rand_131072(b: &mut Bencher) {

#[bench]
fn shl(b: &mut Bencher) {
let n = BigUint::one() << 1000;
let n = BigUint::one() << 1000u32;
let mut m = n.clone();
b.iter(|| {
let mut m = n.clone();
m.clone_from(&n);
for i in 0..50 {
m <<= i;
}
Expand All @@ -304,9 +305,10 @@ fn shl(b: &mut Bencher) {

#[bench]
fn shr(b: &mut Bencher) {
let n = BigUint::one() << 2000;
let n = BigUint::one() << 2000u32;
let mut m = n.clone();
b.iter(|| {
let mut m = n.clone();
m.clone_from(&n);
for i in 0..50 {
m >>= i;
}
Expand Down
74 changes: 50 additions & 24 deletions src/algorithms.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@ use core::cmp;
use core::cmp::Ordering::{self, Equal, Greater, Less};
use core::iter::repeat;
use core::mem;
use num_traits::{One, Zero};
use num_traits::{One, PrimInt, Zero};

use crate::biguint::biguint_from_vec;
use crate::biguint::BigUint;
Expand Down Expand Up @@ -720,34 +720,46 @@ fn div_rem_core(mut a: BigUint, b: &BigUint) -> (BigUint, BigUint) {

/// Find last set bit
/// fls(0) == 0, fls(u32::MAX) == 32
pub(crate) fn fls<T: num_traits::PrimInt>(v: T) -> usize {
pub(crate) fn fls<T: PrimInt>(v: T) -> usize {
mem::size_of::<T>() * 8 - v.leading_zeros() as usize
}

pub(crate) fn ilog2<T: num_traits::PrimInt>(v: T) -> usize {
pub(crate) fn ilog2<T: PrimInt>(v: T) -> usize {
fls(v) - 1
}

#[inline]
pub(crate) fn biguint_shl(n: Cow<'_, BigUint>, bits: usize) -> BigUint {
let n_unit = bits / big_digit::BITS;
let mut data = match n_unit {
pub(crate) fn biguint_shl<T: PrimInt>(n: Cow<'_, BigUint>, shift: T) -> BigUint {
if shift < T::zero() {
panic!("attempt to shift left with negative");
}
if n.is_zero() {
return n.into_owned();
}
let bits = T::from(big_digit::BITS).unwrap();
let digits = (shift / bits).to_usize().expect("capacity overflow");
let shift = (shift % bits).to_u8().unwrap();
biguint_shl2(n, digits, shift)
}

fn biguint_shl2(n: Cow<'_, BigUint>, digits: usize, shift: u8) -> BigUint {
let mut data = match digits {
0 => n.into_owned().data,
_ => {
let len = n_unit + n.data.len() + 1;
let len = digits.saturating_add(n.data.len() + 1);
let mut data = Vec::with_capacity(len);
data.extend(repeat(0).take(n_unit));
data.extend(n.data.iter().cloned());
data.extend(repeat(0).take(digits));
data.extend(n.data.iter());
data
}
};

let n_bits = bits % big_digit::BITS;
if n_bits > 0 {
if shift > 0 {
let mut carry = 0;
for elem in data[n_unit..].iter_mut() {
let new_carry = *elem >> (big_digit::BITS - n_bits);
*elem = (*elem << n_bits) | carry;
let carry_shift = big_digit::BITS as u8 - shift;
for elem in data[digits..].iter_mut() {
let new_carry = *elem >> carry_shift;
*elem = (*elem << shift) | carry;
carry = new_carry;
}
if carry != 0 {
Expand All @@ -759,25 +771,39 @@ pub(crate) fn biguint_shl(n: Cow<'_, BigUint>, bits: usize) -> BigUint {
}

#[inline]
pub(crate) fn biguint_shr(n: Cow<'_, BigUint>, bits: usize) -> BigUint {
let n_unit = bits / big_digit::BITS;
if n_unit >= n.data.len() {
return Zero::zero();
pub(crate) fn biguint_shr<T: PrimInt>(n: Cow<'_, BigUint>, shift: T) -> BigUint {
if shift < T::zero() {
panic!("attempt to shift right with negative");
}
if n.is_zero() {
return n.into_owned();
}
let bits = T::from(big_digit::BITS).unwrap();
let digits = (shift / bits).to_usize().unwrap_or(core::usize::MAX);
let shift = (shift % bits).to_u8().unwrap();
biguint_shr2(n, digits, shift)
}

fn biguint_shr2(n: Cow<'_, BigUint>, digits: usize, shift: u8) -> BigUint {
if digits >= n.data.len() {
let mut n = n.into_owned();
n.set_zero();
return n;
}
let mut data = match n {
Cow::Borrowed(n) => n.data[n_unit..].to_vec(),
Cow::Borrowed(n) => n.data[digits..].to_vec(),
Cow::Owned(mut n) => {
n.data.drain(..n_unit);
n.data.drain(..digits);
n.data
}
};

let n_bits = bits % big_digit::BITS;
if n_bits > 0 {
if shift > 0 {
let mut borrow = 0;
let borrow_shift = big_digit::BITS as u8 - shift;
for elem in data.iter_mut().rev() {
let new_borrow = *elem << (big_digit::BITS - n_bits);
*elem = (*elem >> n_bits) | borrow;
let new_borrow = *elem << borrow_shift;
*elem = (*elem >> shift) | borrow;
borrow = new_borrow;
}
}
Expand Down
144 changes: 90 additions & 54 deletions src/bigint.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@ use serde;

use num_integer::{Integer, Roots};
use num_traits::{
CheckedAdd, CheckedDiv, CheckedMul, CheckedSub, FromPrimitive, Num, One, Pow, Signed,
CheckedAdd, CheckedDiv, CheckedMul, CheckedSub, FromPrimitive, Num, One, Pow, PrimInt, Signed,
ToPrimitive, Zero,
};

Expand Down Expand Up @@ -779,69 +779,105 @@ impl Num for BigInt {
}
}

impl Shl<usize> for BigInt {
type Output = BigInt;
macro_rules! impl_shift {
(@ref $Shx:ident :: $shx:ident, $ShxAssign:ident :: $shx_assign:ident, $rhs:ty) => {
impl<'b> $Shx<&'b $rhs> for BigInt {
type Output = BigInt;

#[inline]
fn shl(mut self, rhs: usize) -> BigInt {
self <<= rhs;
self
}
}
#[inline]
fn $shx(self, rhs: &'b $rhs) -> BigInt {
$Shx::$shx(self, *rhs)
}
}
impl<'a, 'b> $Shx<&'b $rhs> for &'a BigInt {
type Output = BigInt;

impl<'a> Shl<usize> for &'a BigInt {
type Output = BigInt;
#[inline]
fn $shx(self, rhs: &'b $rhs) -> BigInt {
$Shx::$shx(self, *rhs)
}
}
impl<'b> $ShxAssign<&'b $rhs> for BigInt {
#[inline]
fn $shx_assign(&mut self, rhs: &'b $rhs) {
$ShxAssign::$shx_assign(self, *rhs);
}
}
};
($($rhs:ty),+) => {$(
impl Shl<$rhs> for BigInt {
type Output = BigInt;

#[inline]
fn shl(self, rhs: usize) -> BigInt {
BigInt::from_biguint(self.sign, &self.data << rhs)
}
}
#[inline]
fn shl(self, rhs: $rhs) -> BigInt {
BigInt::from_biguint(self.sign, self.data << rhs)
}
}
impl<'a> Shl<$rhs> for &'a BigInt {
type Output = BigInt;

impl ShlAssign<usize> for BigInt {
#[inline]
fn shl_assign(&mut self, rhs: usize) {
self.data <<= rhs;
}
}
#[inline]
fn shl(self, rhs: $rhs) -> BigInt {
BigInt::from_biguint(self.sign, &self.data << rhs)
}
}
impl ShlAssign<$rhs> for BigInt {
#[inline]
fn shl_assign(&mut self, rhs: $rhs) {
self.data <<= rhs
}
}
impl_shift! { @ref Shl::shl, ShlAssign::shl_assign, $rhs }

// Negative values need a rounding adjustment if there are any ones in the
// bits that are getting shifted out.
fn shr_round_down(i: &BigInt, rhs: usize) -> bool {
i.is_negative() && i.trailing_zeros().map(|n| n < rhs).unwrap_or(false)
}
impl Shr<$rhs> for BigInt {
type Output = BigInt;

impl Shr<usize> for BigInt {
type Output = BigInt;
#[inline]
fn shr(self, rhs: $rhs) -> BigInt {
let round_down = shr_round_down(&self, rhs);
let data = self.data >> rhs;
let data = if round_down { data + 1u8 } else { data };
BigInt::from_biguint(self.sign, data)
}
}
impl<'a> Shr<$rhs> for &'a BigInt {
type Output = BigInt;

#[inline]
fn shr(mut self, rhs: usize) -> BigInt {
self >>= rhs;
self
}
#[inline]
fn shr(self, rhs: $rhs) -> BigInt {
let round_down = shr_round_down(self, rhs);
let data = &self.data >> rhs;
let data = if round_down { data + 1u8 } else { data };
BigInt::from_biguint(self.sign, data)
}
}
impl ShrAssign<$rhs> for BigInt {
#[inline]
fn shr_assign(&mut self, rhs: $rhs) {
let round_down = shr_round_down(self, rhs);
self.data >>= rhs;
if round_down {
self.data += 1u8;
} else if self.data.is_zero() {
self.sign = NoSign;
}
}
}
impl_shift! { @ref Shr::shr, ShrAssign::shr_assign, $rhs }
)*};
}

impl<'a> Shr<usize> for &'a BigInt {
type Output = BigInt;

#[inline]
fn shr(self, rhs: usize) -> BigInt {
let round_down = shr_round_down(self, rhs);
let data = &self.data >> rhs;
BigInt::from_biguint(self.sign, if round_down { data + 1u8 } else { data })
}
}
impl_shift! { u8, u16, u32, u64, u128, usize }
impl_shift! { i8, i16, i32, i64, i128, isize }

impl ShrAssign<usize> for BigInt {
#[inline]
fn shr_assign(&mut self, rhs: usize) {
let round_down = shr_round_down(self, rhs);
self.data >>= rhs;
if round_down {
self.data += 1u8;
} else if self.data.is_zero() {
self.sign = NoSign;
}
// Negative values need a rounding adjustment if there are any ones in the
// bits that are getting shifted out.
fn shr_round_down<T: PrimInt>(i: &BigInt, shift: T) -> bool {
if i.is_negative() {
let zeros = i.trailing_zeros().expect("negative values are non-zero");
shift > T::zero() && shift.to_usize().map(|shift| zeros < shift).unwrap_or(true)
} else {
false
}
}

Expand Down