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Simplifies the count_ones definition. #1742

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Dec 26, 2022
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Simplifies the count_ones definition. #1742

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25 changes: 12 additions & 13 deletions fastfield_codecs/src/null_index/dense.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -31,15 +31,16 @@ const BLOCK_BITVEC_SIZE: usize = 8;
const BLOCK_OFFSET_SIZE: usize = 4;
const SERIALIZED_BLOCK_SIZE: usize = BLOCK_BITVEC_SIZE + BLOCK_OFFSET_SIZE;

/// Interpreting the bitvec as a list of 64 bits from the low weight to the
/// high weight.
///
/// This function returns the number of bits set to 1 within
/// `[0..pos_in_vec)`.
#[inline]
fn count_ones(bitvec: u64, pos_in_bitvec: u32) -> u32 {
if pos_in_bitvec == 63 {
bitvec.count_ones()
} else {
let mask = (1u64 << (pos_in_bitvec + 1)) - 1;
let masked_bitvec = bitvec & mask;
masked_bitvec.count_ones()
}
let mask = (1u64 << pos_in_bitvec) - 1;
let masked_bitvec = bitvec & mask;
masked_bitvec.count_ones()
}

#[derive(Clone, Copy)]
Expand All @@ -66,9 +67,7 @@ impl DenseCodec {
pub fn exists(&self, idx: u32) -> bool {
let block_pos = idx / ELEMENTS_PER_BLOCK;
let bitvec = self.dense_index_block(block_pos).bitvec;

let pos_in_bitvec = idx % ELEMENTS_PER_BLOCK;

get_bit_at(bitvec, pos_in_bitvec)
}
#[inline]
Expand All @@ -90,8 +89,7 @@ impl DenseCodec {
let pos_in_block_bit_vec = idx % ELEMENTS_PER_BLOCK;
let ones_in_block = count_ones(index_block.bitvec, pos_in_block_bit_vec);
if get_bit_at(index_block.bitvec, pos_in_block_bit_vec) {
// -1 is ok, since idx does exist, so there's at least one
Some(index_block.offset + ones_in_block - 1)
Some(index_block.offset + ones_in_block)
} else {
None
}
Expand Down Expand Up @@ -319,9 +317,10 @@ mod tests {
set_bit_at(&mut block, 0);
set_bit_at(&mut block, 2);

assert_eq!(count_ones(block, 0), 1);
assert_eq!(count_ones(block, 0), 0);
assert_eq!(count_ones(block, 1), 1);
assert_eq!(count_ones(block, 2), 2);
assert_eq!(count_ones(block, 2), 1);
assert_eq!(count_ones(block, 3), 2);
}
}

Expand Down