Compute asymmetric ADC distance from a prepared query to a PQ-encoded candidate. Expects `PreparedQuery::Lut` produced by `prepare_query`.
(
&self,
prepared: &PreparedQuery,
encoded: &[u8],
)
| 132 | /// |
| 133 | /// Expects `PreparedQuery::Lut` produced by `prepare_query`. |
| 134 | fn distance_prepared( |
| 135 | &self, |
| 136 | prepared: &PreparedQuery, |
| 137 | encoded: &[u8], |
| 138 | ) -> Result<f32, RerankError> { |
| 139 | let lut = match prepared { |
| 140 | PreparedQuery::Lut(t) => t, |
| 141 | _ => { |
| 142 | return Err(RerankError::BadInput( |
| 143 | "pq distance: expected PreparedQuery::Lut".to_string(), |
| 144 | )); |
| 145 | } |
| 146 | }; |
| 147 | |
| 148 | let packed_len = pq_packed_bits_len(self.m); |
| 149 | let uqv_ref = UnifiedQuantizedVectorRef::from_bytes(encoded, packed_len).map_err(|e| { |
| 150 | RerankError::BadInput(format!("pq distance: failed to parse encoded bytes: {e}")) |
| 151 | })?; |
| 152 | |
| 153 | let packed = uqv_ref.packed_bits(); |
| 154 | // ADC: sum lut[sub][code[sub]] for each subspace. |
| 155 | let dist = packed |
| 156 | .iter() |
| 157 | .enumerate() |
| 158 | .map(|(sub, &code)| { |
| 159 | lut.get(sub) |
| 160 | .and_then(|row| row.get(code as usize).copied()) |
| 161 | .unwrap_or(0.0) |
| 162 | }) |
| 163 | .sum(); |
| 164 | Ok(dist) |
| 165 | } |
| 166 | |
| 167 | fn name(&self) -> CodecName { |
| 168 | CodecName::Pq |