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fix: Write bits to bytes in LSB #9

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Merged
rustaceanrob merged 1 commit into from
Oct 9, 2026
Merged

fix: Write bits to bytes in LSB #9

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20 changes: 16 additions & 4 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@ impl EliasFano {
let low = element & mask;
for shift in 0..l {
let bit = ((low >> shift) & 1) as u8;
curr_byte |= bit << (7 - bit_pos);
curr_byte |= bit << bit_pos;
bit_pos += 1;
if bit_pos == 8 {
packed.push(curr_byte);
Expand Down Expand Up @@ -81,7 +81,7 @@ impl EliasFano {
curr_byte = 0x00;
}
}
curr_byte |= 1 << (7 - bit_pos);
curr_byte |= 1 << bit_pos;
bit_pos += 1;
if bit_pos == 8 {
high.push(curr_byte);
Expand Down Expand Up @@ -110,7 +110,7 @@ impl EliasFano {
for _ in 0..self.n {
let mut low_val: u32 = 0;
for shift in 0..l {
let bit = (self.low[low_byte_pos] >> (7 - low_bit_pos)) & 1;
let bit = (self.low[low_byte_pos] >> low_bit_pos) & 1;
low_val |= (bit as u32) << shift;
low_bit_pos += 1;
if low_bit_pos == 8 {
Expand All @@ -119,7 +119,7 @@ impl EliasFano {
}
}
loop {
let bit = (self.high[high_byte_pos] >> (7 - high_bit_pos)) & 1;
let bit = (self.high[high_byte_pos] >> high_bit_pos) & 1;
high_bit_pos += 1;
if high_bit_pos == 8 {
high_byte_pos += 1;
Expand Down Expand Up @@ -430,6 +430,18 @@ mod tests {

use super::EliasFano;

#[test]
fn lsb_first_bit_order() {
// Lows 3, 3, 0 pack bit 0 first into bits 0..5; highs 0, 1, 3 unary `1 01 001`.
let elms = vec![3, 7, 12];
let ef = EliasFano::compress(&elms);
let mut bytes = Vec::new();
ef.write(&mut bytes).unwrap();
assert_eq!(bytes, vec![0x03, 0x0c, 0x0f, 0x25]);
let ef = EliasFano::from_reader(&mut bytes.as_slice()).unwrap();
assert_eq!(ef.decompress(), elms);
}

#[test]
fn compress_decompress() {
let mut elms = Vec::new();
Expand Down
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