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# fix: Replace slower division and remainder with faster bit operations and addition #133

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# fix: Replace slower division and remainder with faster bit operations and addition #133

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1 change: 1 addition & 0 deletions src/block/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,7 @@ impl Block {
pub const NONE: Self = Self::from_usize_array([0; Self::USIZE_COUNT]);
pub const ALL: Self = Self::from_usize_array([usize::MAX; Self::USIZE_COUNT]);
pub const BITS: usize = core::mem::size_of::<Self>() * 8;
pub const BITS_LOG2: usize = usize::ilog2(Self::BITS) as usize;

#[inline]
pub fn into_usize_array(self) -> [usize; Self::USIZE_COUNT] {
Expand Down
39 changes: 24 additions & 15 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -40,15 +40,24 @@ use core::ptr::NonNull;
pub use range::IndexRange;

pub(crate) const BITS: usize = core::mem::size_of::<Block>() * 8;
pub const BITS_LOG2: usize = usize::ilog2(BITS) as usize;
#[cfg(feature = "serde")]
pub(crate) const BYTES: usize = core::mem::size_of::<Block>();

use block::Block as SimdBlock;
pub type Block = usize;

// #[inline]
// fn div_rem(x: usize, mut denominator: usize, _bitslog2: usize) -> (usize, usize) {
// denominator = usize::pow(2, denominator as u32) ;
// (x / denominator, x % denominator)
// }

#[inline]
fn div_rem(x: usize, denominator: usize) -> (usize, usize) {
(x / denominator, x % denominator)
fn div_rem(x: usize, bits: usize, bitslog2: usize) -> (usize, usize) {
let block = x >> bitslog2;
let i = x - (block * bits);
(block, i)
}

fn vec_into_parts<T>(vec: Vec<T>) -> (NonNull<T>, usize, usize) {
Expand Down Expand Up @@ -96,7 +105,7 @@ impl FixedBitSet {
/// Create a new **FixedBitSet** with a specific number of bits,
/// all initially clear.
pub fn with_capacity(bits: usize) -> Self {
let (mut blocks, rem) = div_rem(bits, SimdBlock::BITS);
let (mut blocks, rem) = div_rem(bits, SimdBlock::BITS, SimdBlock::BITS_LOG2);
blocks += (rem > 0) as usize;
Self::from_blocks_and_len(vec![SimdBlock::NONE; blocks], bits)
}
Expand Down Expand Up @@ -158,7 +167,7 @@ impl FixedBitSet {
let mut data = unsafe {
Vec::from_raw_parts(self.data.as_ptr(), self.simd_block_len(), self.capacity)
};
let (mut blocks, rem) = div_rem(bits, SimdBlock::BITS);
let (mut blocks, rem) = div_rem(bits, SimdBlock::BITS, SimdBlock::BITS_LOG2);
blocks += (rem > 0) as usize;
data.resize(blocks, fill);
let (data, capacity, _) = vec_into_parts(data);
Expand All @@ -179,14 +188,14 @@ impl FixedBitSet {

#[inline]
fn usize_len(&self) -> usize {
let (mut blocks, rem) = div_rem(self.length, BITS);
let (mut blocks, rem) = div_rem(self.length, BITS, BITS_LOG2);
blocks += (rem > 0) as usize;
blocks
}

#[inline]
fn simd_block_len(&self) -> usize {
let (mut blocks, rem) = div_rem(self.length, SimdBlock::BITS);
let (mut blocks, rem) = div_rem(self.length, SimdBlock::BITS, SimdBlock::BITS_LOG2);
blocks += (rem > 0) as usize;
blocks
}
Expand Down Expand Up @@ -233,7 +242,7 @@ impl FixedBitSet {
pub fn grow_and_insert(&mut self, bits: usize) {
self.grow(bits + 1);

let (blocks, rem) = div_rem(bits, BITS);
let (blocks, rem) = div_rem(bits, BITS, BITS_LOG2);
// SAFETY: The above grow ensures that the block is inside the Vec's allocation.
unsafe {
*self.get_unchecked_mut(blocks) |= 1 << rem;
Expand Down Expand Up @@ -406,7 +415,7 @@ impl FixedBitSet {
/// `bit` must be less than `self.len()`
#[inline]
pub unsafe fn contains_unchecked(&self, bit: usize) -> bool {
let (block, i) = div_rem(bit, BITS);
let (block, i) = div_rem(bit, BITS, BITS_LOG2);
(self.get_unchecked(block) & (1 << i)) != 0
}

Expand Down Expand Up @@ -441,7 +450,7 @@ impl FixedBitSet {
/// `bit` must be less than `self.len()`
#[inline]
pub unsafe fn insert_unchecked(&mut self, bit: usize) {
let (block, i) = div_rem(bit, BITS);
let (block, i) = div_rem(bit, BITS, BITS_LOG2);
// SAFETY: The above assertion ensures that the block is inside the Vec's allocation.
unsafe {
*self.get_unchecked_mut(block) |= 1 << i;
Expand Down Expand Up @@ -471,7 +480,7 @@ impl FixedBitSet {
/// `bit` must be less than `self.len()`
#[inline]
pub unsafe fn remove_unchecked(&mut self, bit: usize) {
let (block, i) = div_rem(bit, BITS);
let (block, i) = div_rem(bit, BITS, BITS_LOG2);
// SAFETY: The above assertion ensures that the block is inside the Vec's allocation.
unsafe {
*self.get_unchecked_mut(block) &= !(1 << i);
Expand Down Expand Up @@ -499,7 +508,7 @@ impl FixedBitSet {
/// `bit` must be less than `self.len()`
#[inline]
pub unsafe fn put_unchecked(&mut self, bit: usize) -> bool {
let (block, i) = div_rem(bit, BITS);
let (block, i) = div_rem(bit, BITS, BITS_LOG2);
// SAFETY: The above assertion ensures that the block is inside the Vec's allocation.
unsafe {
let word = self.get_unchecked_mut(block);
Expand Down Expand Up @@ -532,7 +541,7 @@ impl FixedBitSet {
/// `bit` must be less than `self.len()`
#[inline]
pub unsafe fn toggle_unchecked(&mut self, bit: usize) {
let (block, i) = div_rem(bit, BITS);
let (block, i) = div_rem(bit, BITS, BITS_LOG2);
// SAFETY: The above assertion ensures that the block is inside the Vec's allocation.
unsafe {
*self.get_unchecked_mut(block) ^= 1 << i;
Expand Down Expand Up @@ -562,7 +571,7 @@ impl FixedBitSet {
/// `bit` must be less than `self.len()`
#[inline]
pub unsafe fn set_unchecked(&mut self, bit: usize, enabled: bool) {
let (block, i) = div_rem(bit, BITS);
let (block, i) = div_rem(bit, BITS, BITS_LOG2);
// SAFETY: The above assertion ensures that the block is inside the Vec's allocation.
let elt = unsafe { self.get_unchecked_mut(block) };
if enabled {
Expand Down Expand Up @@ -1230,8 +1239,8 @@ impl Masks {
length
);

let (first_block, first_rem) = div_rem(start, BITS);
let (last_block, last_rem) = div_rem(end, BITS);
let (first_block, first_rem) = div_rem(start, BITS, BITS_LOG2);
let (last_block, last_rem) = div_rem(end, BITS, BITS_LOG2);

Masks {
first_block,
Expand Down
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