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document 1 unused bit in skiplist

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trinity Pointard
2025-12-19 10:29:43 +01:00
parent 53c4b8346c
commit 32a8f8646f
1 changed files with 8 additions and 4 deletions
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12
src/postings/skip.rs
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@@ -6,17 +6,21 @@ use crate::{DocId, Score, TERMINATED};
// doc num bits uses the following encoding:
// given 0b a b cdefgh
// |1|2| 3 |
// |1|2|3| 4 |
// - 1: unused
// - 2: is delta-1 encoded. 0 if not, 1, if yes
// - 3: a 6 bit number in 0..=32, the actual bitwidth
// - 3: unused
// - 4: a 5 bit number in 0..32, the actual bitwidth. Bitpacking could in theory say this is 32
// (requiring a 6th bit), but the biggest doc_id we can want to encode is TERMINATED-1, which can
// be represented on 31b without delta encoding.
fn encode_bitwidth(bitwidth: u8, delta_1: bool) -> u8 {
assert!(bitwidth < 32);
bitwidth | ((delta_1 as u8) << 6)
}
fn decode_bitwidth(raw_bitwidth: u8) -> (u8, bool) {
let delta_1 = ((raw_bitwidth >> 6) & 1) != 0;
let bitwidth = raw_bitwidth & 0x3f;
let bitwidth = raw_bitwidth & 0x1f;
(bitwidth, delta_1)
}
@@ -430,7 +434,7 @@ mod tests {
#[test]
fn test_encode_decode_bitwidth() {
for bitwidth in 0..=32 {
for bitwidth in 0..32 {
for delta_1 in [false, true] {
assert_eq!(
(bitwidth, delta_1),