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remove dead code
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@jorendorff
jorendorff committed Nov 12, 2024
1 parent 2fcc903 commit bfaa2de
Showing 1 changed file with 26 additions and 155 deletions.
181 changes: 26 additions & 155 deletions crates/string-offsets/src/bitrank.rs
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Original file line number Diff line number Diff line change
@@ -1,9 +1,6 @@
//! A bit-vector data structure, optimized for
//! [rank](http://bitmagic.io/rank-select.html) operations.
//!
//! There is also an opportunistic `select` operation, but the general case has not been
//! implemented.
//!
//! See also: ["Succinct data structure"](https://en.wikipedia.org/wiki/Succinct_data_structure).
type SubblockBits = u128;
Expand Down Expand Up @@ -55,15 +52,6 @@ impl Block {
self.bits[chunk_idx] ^= mask;
}

/// Tests whether the bit at the given index is set.
fn get(&self, index: usize) -> bool {
assert!(index < BITS_PER_BLOCK);
let chunk_idx = index / BITS_PER_SUB_BLOCK;
let bit_idx = index % BITS_PER_SUB_BLOCK;
let mask = 1 << ((BITS_PER_SUB_BLOCK - 1) - bit_idx);
self.bits[chunk_idx] & mask != 0
}

/// The **total rank** of the block relative local index, and the index of the one
/// bit that establishes that rank (aka "select") **if** it occurs within that same
/// chunk, otherwise ['None']. The assumption is that if you would have to look back
Expand Down Expand Up @@ -99,40 +87,6 @@ impl Block {
.map(|c| c.count_ones() as usize)
.sum::<usize>()
}

fn predecessor(&self, idx: usize) -> Option<usize> {
let sub_block = idx / BITS_PER_SUB_BLOCK;
let masked = self.bits[sub_block] >> (BITS_PER_SUB_BLOCK - 1 - idx % BITS_PER_SUB_BLOCK);
if masked > 0 {
Some(idx - masked.trailing_zeros() as usize)
} else {
for i in (0..sub_block).rev() {
let masked = self.bits[i];
if masked > 0 {
return Some(
(i + 1) * BITS_PER_SUB_BLOCK - masked.trailing_zeros() as usize - 1,
);
}
}
None
}
}

fn successor(&self, idx: usize) -> Option<usize> {
let sub_block = idx / BITS_PER_SUB_BLOCK;
let masked = self.bits[sub_block] << (idx % BITS_PER_SUB_BLOCK);
if masked > 0 {
Some(idx + masked.leading_zeros() as usize)
} else {
for i in (sub_block + 1)..SUB_BLOCKS_PER_BLOCK {
let masked = self.bits[i];
if masked > 0 {
return Some(i * BITS_PER_SUB_BLOCK + masked.leading_zeros() as usize);
}
}
None
}
}
}

/// Builder for creating a [`BitRank`].
Expand All @@ -154,6 +108,7 @@ pub struct BitRankBuilder {

impl BitRankBuilder {
/// Returns a new builder.
#[cfg(test)]
pub fn new() -> Self {
Self::default()
}
Expand Down Expand Up @@ -221,20 +176,6 @@ pub struct BitRank {
}

impl BitRank {
/// Creates a `BitRank` containing the integers in `iter`.
///
/// # Panics
/// This may panic if the values produced by `iter` are not strictly increasing.
#[allow(dead_code)]
#[allow(clippy::should_implement_trait)]
pub fn from_iter<I: IntoIterator<Item = usize>>(iter: I) -> BitRank {
let mut builder = BitRankBuilder::new();
for position in iter {
builder.push(position);
}
builder.finish()
}

/// The rank at the specified index (exclusive).
///
/// The (one) rank is defined as: `rank(i) = sum(b[j] for j in 0..i)`
Expand All @@ -243,51 +184,6 @@ impl BitRank {
self.rank_select(idx).0
}

/// Tests whether the bit at the given index is set.
#[allow(dead_code)]
pub fn get(&self, idx: usize) -> bool {
let block_num = idx / BITS_PER_BLOCK;
// assert!(block_num < self.blocks.len(), "index out of bounds");
if block_num >= self.blocks.len() {
false
} else {
self.blocks[block_num].get(idx % BITS_PER_BLOCK)
}
}

/// Returns the 1 bit at or before the specified index.
#[allow(dead_code)]
pub fn predecessor(&self, idx: usize) -> usize {
let block_num = idx / BITS_PER_BLOCK;
if block_num < self.blocks.len() {
if let Some(p) = self.blocks[block_num].predecessor(idx % BITS_PER_BLOCK) {
return block_num * BITS_PER_BLOCK + p;
}
}
for block_num in (0..self.blocks.len().min(block_num)).rev() {
if let Some(p) = self.blocks[block_num].predecessor(BITS_PER_BLOCK - 1) {
return block_num * BITS_PER_BLOCK + p;
}
}
panic!("no predecessor found!");
}

/// Returns the next 1 bit at or after the specified index.
#[allow(dead_code)]
pub fn successor(&self, idx: usize) -> usize {
let block_num = idx / BITS_PER_BLOCK;
if let Some(s) = self.blocks[block_num].successor(idx % BITS_PER_BLOCK) {
s + block_num * BITS_PER_BLOCK
} else {
for block_num in block_num + 1..self.blocks.len() {
if let Some(p) = self.blocks[block_num].successor(0) {
return block_num * BITS_PER_BLOCK + p;
}
}
panic!("no successor found!");
}
}

/// Returns the number of elements in the set.
pub fn max_rank(&self) -> usize {
self.blocks
Expand All @@ -314,58 +210,55 @@ impl BitRank {
(rank, b_idx.map(|i| (block_num * BITS_PER_BLOCK) + i))
}
}

/// The total size of the bit vec that was allocated.
/// **Note:** This is more like capacity than normal `len` in that it does not
/// consider how much of the bit vec is actually used.
#[allow(dead_code)]
pub fn capacity(&self) -> usize {
self.blocks.len() * BITS_PER_BLOCK
}
}

#[cfg(test)]
mod tests {
use itertools::Itertools;
use rand::distributions::Uniform;
use rand::prelude::*;
use rand_chacha::ChaCha8Rng;

use super::*;

fn write(positions: &[usize]) -> BitRank {
BitRank::from_iter(positions.iter().copied())
/// Creates a `BitRank` containing the integers in `iter` (which should be strictly
/// increasing).
pub fn bitrank<I: IntoIterator<Item = usize>>(iter: I) -> BitRank {
let mut builder = BitRankBuilder::new();
for position in iter {
builder.push(position);
}
builder.finish()
}

#[test]
fn test_rank_zero() {
let br = BitRank::from_iter([0]);
let br = bitrank([0]);
assert_eq!(br.rank(0), 0);
assert_eq!(br.rank(1), 1);
}

#[test]
fn test_empty() {
let br = BitRank::from_iter([]);
let br = bitrank([]);
assert!(br.blocks.is_empty());
}

#[test]
fn test_index_out_of_bounds() {
let br = BitRank::from_iter([BITS_PER_BLOCK - 1]);
let br = bitrank([BITS_PER_BLOCK - 1]);
assert_eq!(br.rank(BITS_PER_BLOCK), 1);
}

#[test]
#[should_panic]
fn test_duplicate_position() {
write(&[64, 66, 68, 68, 90]);
bitrank([64, 66, 68, 68, 90]);
}

#[test]
fn test_rank_exclusive() {
let br = BitRank::from_iter(0..132);
assert_eq!(br.capacity(), BITS_PER_BLOCK);
let br = bitrank(0..132);
assert_eq!(br.blocks.len(), 1);
assert_eq!(br.rank(64), 64);
assert_eq!(br.rank(132), 132);
}
Expand All @@ -374,39 +267,37 @@ mod tests {
fn test_rank() {
let mut positions: Vec<usize> = (0..132).collect();
positions.append(&mut vec![138usize, 140, 146]);
let br = write(&positions);
let br = bitrank(positions);
assert_eq!(br.rank(135), 132);

let bits2: Vec<usize> = (0..BITS_PER_BLOCK - 5).collect();
let br2 = write(&bits2);
let br2 = bitrank(0..BITS_PER_BLOCK - 5);
assert_eq!(br2.rank(169), 169);

let bits3: Vec<usize> = (0..BITS_PER_BLOCK + 5).collect();
let br3 = write(&bits3);
let br3 = bitrank(0..BITS_PER_BLOCK + 5);
assert_eq!(br3.rank(BITS_PER_BLOCK), BITS_PER_BLOCK);
}

#[test]
fn test_rank_idx() {
let mut positions: Vec<usize> = (0..132).collect();
positions.append(&mut vec![138usize, 140, 146]);
let br = write(&positions);
let br = bitrank(positions);
assert_eq!(br.rank_select(135), (132, Some(131)));

let bits2: Vec<usize> = (0..BITS_PER_BLOCK - 5).collect();
let br2 = write(&bits2);
let br2 = bitrank(bits2);
assert_eq!(br2.rank_select(169), (169, Some(168)));

let bits3: Vec<usize> = (0..BITS_PER_BLOCK + 5).collect();
let br3 = write(&bits3);
let br3 = bitrank(bits3);
assert_eq!(br3.rank_select(BITS_PER_BLOCK), (BITS_PER_BLOCK, None));

let bits4: Vec<usize> = vec![1, 1000, 9999, BITS_PER_BLOCK + 1];
let br4 = write(&bits4);
let br4 = bitrank(bits4);
assert_eq!(br4.rank_select(10000), (3, Some(9999)));

let bits5: Vec<usize> = vec![1, 1000, 9999, BITS_PER_BLOCK + 1];
let br5 = write(&bits5);
let br5 = bitrank(bits5);
assert_eq!(br5.rank_select(BITS_PER_BLOCK), (3, None));
}

Expand All @@ -422,7 +313,7 @@ mod tests {
// This isn't strictly necessary, given that the bit would just be toggled again, but it
// ensures that we are meeting the contract.
random_bits.dedup();
let br = write(&random_bits);
let br = bitrank(random_bits.iter().copied());
let mut rank = 0;
let mut select = None;
for i in 0..random_bits.capacity() {
Expand All @@ -442,7 +333,7 @@ mod tests {
#[test]
fn test_rank_out_of_bounds() {
for i in 1..30 {
let br = write(&[BITS_PER_BLOCK * i - 1]);
let br = bitrank([BITS_PER_BLOCK * i - 1]);
assert_eq!(br.max_rank(), 1);
assert_eq!(br.rank(BITS_PER_BLOCK * i - 1), 0);
for j in 0..10 {
Expand All @@ -451,29 +342,9 @@ mod tests {
}
}

#[test]
fn test_predecessor_and_successor() {
let mut rng = ChaCha8Rng::seed_from_u64(2);
let uniform = Uniform::<usize>::from(0..1_000_000);
let mut random_bits = Vec::with_capacity(100_000);
for _ in 0..100_000 {
random_bits.push(uniform.sample(&mut rng));
}
random_bits.sort_unstable();
random_bits.dedup();
let br = write(&random_bits);

for (i, j) in random_bits.iter().copied().tuple_windows() {
for k in i..j {
assert_eq!(br.successor(k + 1), j, "{i} {k} {j}");
assert_eq!(br.predecessor(k), i, "{i} {k} {j}");
}
}
}

#[test]
fn test_large_gap() {
let br = BitRank::from_iter((3..4).chain(BITS_PER_BLOCK * 15..BITS_PER_BLOCK * 15 + 17));
let br = bitrank((3..4).chain(BITS_PER_BLOCK * 15..BITS_PER_BLOCK * 15 + 17));
for i in 1..15 {
assert_eq!(br.rank(BITS_PER_BLOCK * i), 1);
}
Expand Down

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