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Split ScalarQuantizer code into independent parts (#4296) #4557

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291b256
SIMDConfig object, [faiss] Adding support for AVX2 and AVX512(F, BW, …
mdouze Aug 28, 2025
3c61326
dynamic dispatch distances_simd
mdouze Aug 28, 2025
18ffaa7
moved IndexIVFPQ and IndexPQ to dynamic dispatch (#4291)
mdouze Aug 28, 2025
9735216
Use simdlib abstraction in ScalarQuantizer implementation, split off …
mdouze Aug 28, 2025
e4aab93
Split ScalarQuantizer code into independent parts (#4557)
Aug 28, 2025
4e9ef40
Merge branch 'main' into export-D73037185
junjieqi Sep 10, 2025
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68 changes: 41 additions & 27 deletions faiss/IndexIVFPQ.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -817,8 +817,9 @@ struct RangeSearchResults {
* The scanning functions call their favorite precompute_*
* function to precompute the tables they need.
*****************************************************/
template <typename IDType, MetricType METRIC_TYPE, class PQDecoder>
template <typename IDType, MetricType METRIC_TYPE, class PQCodeDistance>
struct IVFPQScannerT : QueryTables {
using PQDecoder = typename PQCodeDistance::PQDecoder;
const uint8_t* list_codes;
const IDType* list_ids;
size_t list_size;
Expand Down Expand Up @@ -894,7 +895,7 @@ struct IVFPQScannerT : QueryTables {
float distance_1 = 0;
float distance_2 = 0;
float distance_3 = 0;
distance_four_codes<PQDecoder>(
PQCodeDistance::distance_four_codes(
pq.M,
pq.nbits,
sim_table,
Expand All @@ -917,7 +918,7 @@ struct IVFPQScannerT : QueryTables {

if (counter >= 1) {
float dis = dis0 +
distance_single_code<PQDecoder>(
PQCodeDistance::distance_single_code(
pq.M,
pq.nbits,
sim_table,
Expand All @@ -926,7 +927,7 @@ struct IVFPQScannerT : QueryTables {
}
if (counter >= 2) {
float dis = dis0 +
distance_single_code<PQDecoder>(
PQCodeDistance::distance_single_code(
pq.M,
pq.nbits,
sim_table,
Expand All @@ -935,7 +936,7 @@ struct IVFPQScannerT : QueryTables {
}
if (counter >= 3) {
float dis = dis0 +
distance_single_code<PQDecoder>(
PQCodeDistance::distance_single_code(
pq.M,
pq.nbits,
sim_table,
Expand Down Expand Up @@ -1101,7 +1102,7 @@ struct IVFPQScannerT : QueryTables {
float distance_1 = dis0;
float distance_2 = dis0;
float distance_3 = dis0;
distance_four_codes<PQDecoder>(
PQCodeDistance::distance_four_codes(
pq.M,
pq.nbits,
sim_table,
Expand Down Expand Up @@ -1132,7 +1133,7 @@ struct IVFPQScannerT : QueryTables {
n_hamming_pass++;

float dis = dis0 +
distance_single_code<PQDecoder>(
PQCodeDistance::distance_single_code(
pq.M,
pq.nbits,
sim_table,
Expand All @@ -1152,7 +1153,7 @@ struct IVFPQScannerT : QueryTables {
n_hamming_pass++;

float dis = dis0 +
distance_single_code<PQDecoder>(
PQCodeDistance::distance_single_code(
pq.M,
pq.nbits,
sim_table,
Expand Down Expand Up @@ -1197,8 +1198,8 @@ struct IVFPQScannerT : QueryTables {
*
* use_sel: store or ignore the IDSelector
*/
template <MetricType METRIC_TYPE, class C, class PQDecoder, bool use_sel>
struct IVFPQScanner : IVFPQScannerT<idx_t, METRIC_TYPE, PQDecoder>,
template <MetricType METRIC_TYPE, class C, class PQCodeDistance, bool use_sel>
struct IVFPQScanner : IVFPQScannerT<idx_t, METRIC_TYPE, PQCodeDistance>,
InvertedListScanner {
int precompute_mode;
const IDSelector* sel;
Expand All @@ -1208,7 +1209,7 @@ struct IVFPQScanner : IVFPQScannerT<idx_t, METRIC_TYPE, PQDecoder>,
bool store_pairs,
int precompute_mode,
const IDSelector* sel)
: IVFPQScannerT<idx_t, METRIC_TYPE, PQDecoder>(ivfpq, nullptr),
: IVFPQScannerT<idx_t, METRIC_TYPE, PQCodeDistance>(ivfpq, nullptr),
precompute_mode(precompute_mode),
sel(sel) {
this->store_pairs = store_pairs;
Expand All @@ -1228,7 +1229,7 @@ struct IVFPQScanner : IVFPQScannerT<idx_t, METRIC_TYPE, PQDecoder>,
float distance_to_code(const uint8_t* code) const override {
assert(precompute_mode == 2);
float dis = this->dis0 +
distance_single_code<PQDecoder>(
PQCodeDistance::distance_single_code(
this->pq.M, this->pq.nbits, this->sim_table, code);
return dis;
}
Expand Down Expand Up @@ -1292,7 +1293,9 @@ struct IVFPQScanner : IVFPQScannerT<idx_t, METRIC_TYPE, PQDecoder>,
}
};

template <class PQDecoder, bool use_sel>
/** follow 3 stages of template dispatching */

template <class PQCodeDistance, bool use_sel>
InvertedListScanner* get_InvertedListScanner1(
const IndexIVFPQ& index,
bool store_pairs,
Expand All @@ -1301,32 +1304,47 @@ InvertedListScanner* get_InvertedListScanner1(
return new IVFPQScanner<
METRIC_INNER_PRODUCT,
CMin<float, idx_t>,
PQDecoder,
PQCodeDistance,
use_sel>(index, store_pairs, 2, sel);
} else if (index.metric_type == METRIC_L2) {
return new IVFPQScanner<
METRIC_L2,
CMax<float, idx_t>,
PQDecoder,
PQCodeDistance,
use_sel>(index, store_pairs, 2, sel);
}
return nullptr;
}

template <bool use_sel>
template <bool use_sel, SIMDLevel SL>
InvertedListScanner* get_InvertedListScanner2(
const IndexIVFPQ& index,
bool store_pairs,
const IDSelector* sel) {
if (index.pq.nbits == 8) {
return get_InvertedListScanner1<PQDecoder8, use_sel>(
index, store_pairs, sel);
return get_InvertedListScanner1<
PQCodeDistance<PQDecoder8, SL>,
use_sel>(index, store_pairs, sel);
} else if (index.pq.nbits == 16) {
return get_InvertedListScanner1<PQDecoder16, use_sel>(
index, store_pairs, sel);
return get_InvertedListScanner1<
PQCodeDistance<PQDecoder16, SL>,
use_sel>(index, store_pairs, sel);
} else {
return get_InvertedListScanner1<
PQCodeDistance<PQDecoderGeneric, SL>,
use_sel>(index, store_pairs, sel);
}
}

template <SIMDLevel SL>
InvertedListScanner* get_InvertedListScanner3(
const IndexIVFPQ& index,
bool store_pairs,
const IDSelector* sel) {
if (sel) {
return get_InvertedListScanner2<true, SL>(index, store_pairs, sel);
} else {
return get_InvertedListScanner1<PQDecoderGeneric, use_sel>(
index, store_pairs, sel);
return get_InvertedListScanner2<false, SL>(index, store_pairs, sel);
}
}

Expand All @@ -1336,11 +1354,7 @@ InvertedListScanner* IndexIVFPQ::get_InvertedListScanner(
bool store_pairs,
const IDSelector* sel,
const IVFSearchParameters*) const {
if (sel) {
return get_InvertedListScanner2<true>(*this, store_pairs, sel);
} else {
return get_InvertedListScanner2<false>(*this, store_pairs, sel);
}
DISPATCH_SIMDLevel(get_InvertedListScanner3, *this, store_pairs, sel);
return nullptr;
}

Expand Down
32 changes: 21 additions & 11 deletions faiss/IndexPQ.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -72,7 +72,7 @@ void IndexPQ::train(idx_t n, const float* x) {

namespace {

template <class PQDecoder>
template <class PQCodeDistance>
struct PQDistanceComputer : FlatCodesDistanceComputer {
size_t d;
MetricType metric;
Expand All @@ -85,7 +85,7 @@ struct PQDistanceComputer : FlatCodesDistanceComputer {
float distance_to_code(const uint8_t* code) final {
ndis++;

float dis = distance_single_code<PQDecoder>(
float dis = PQCodeDistance::distance_single_code(
pq.M, pq.nbits, precomputed_table.data(), code);
return dis;
}
Expand All @@ -94,8 +94,10 @@ struct PQDistanceComputer : FlatCodesDistanceComputer {
FAISS_THROW_IF_NOT(sdc);
const float* sdci = sdc;
float accu = 0;
PQDecoder codei(codes + i * code_size, pq.nbits);
PQDecoder codej(codes + j * code_size, pq.nbits);
typename PQCodeDistance::PQDecoder codei(
codes + i * code_size, pq.nbits);
typename PQCodeDistance::PQDecoder codej(
codes + j * code_size, pq.nbits);

for (int l = 0; l < pq.M; l++) {
accu += sdci[codei.decode() + (codej.decode() << codei.nbits)];
Expand Down Expand Up @@ -131,16 +133,24 @@ struct PQDistanceComputer : FlatCodesDistanceComputer {
}
};

template <SIMDLevel SL>
FlatCodesDistanceComputer* get_FlatCodesDistanceComputer1(
const IndexPQ& index) {
int nbits = index.pq.nbits;
if (nbits == 8) {
return new PQDistanceComputer<PQCodeDistance<PQDecoder8, SL>>(index);
} else if (nbits == 16) {
return new PQDistanceComputer<PQCodeDistance<PQDecoder16, SL>>(index);
} else {
return new PQDistanceComputer<PQCodeDistance<PQDecoderGeneric, SL>>(
index);
}
}

} // namespace

FlatCodesDistanceComputer* IndexPQ::get_FlatCodesDistanceComputer() const {
if (pq.nbits == 8) {
return new PQDistanceComputer<PQDecoder8>(*this);
} else if (pq.nbits == 16) {
return new PQDistanceComputer<PQDecoder16>(*this);
} else {
return new PQDistanceComputer<PQDecoderGeneric>(*this);
}
DISPATCH_SIMDLevel(get_FlatCodesDistanceComputer1, *this);
}

/*****************************************
Expand Down
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