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/data/users/matthijs/github_faiss/faiss/IndexScalarQuantizer.h
1 /**
2 * Copyright (c) 2015-present, Facebook, Inc.
3 * All rights reserved.
4 *
5 * This source code is licensed under the BSD+Patents license found in the
6 * LICENSE file in the root directory of this source tree.
7 */
8
9 #ifndef FAISS_INDEX_SCALAR_QUANTIZER_H
10 #define FAISS_INDEX_SCALAR_QUANTIZER_H
11
12 #include <stdint.h>
13
14
15 #include <vector>
16
17
18 #include "IndexIVF.h"
19
20
21 namespace faiss {
22
23 /**
24 * The uniform quantizer has a range [vmin, vmax]. The range can be
25 * the same for all dimensions (uniform) or specific per dimension
26 * (default).
27 */
28
29
30 struct ScalarQuantizer {
31
32 enum QuantizerType {
33 QT_8bit, ///< 8 bits per component
34 QT_4bit, ///< 4 bits per component
35 QT_8bit_uniform, ///< same, shared range for all dimensions
36 QT_4bit_uniform,
37 };
38
39 QuantizerType qtype;
40
41 /** The uniform encoder can estimate the range of representable
42 * values of the unform encoder using different statistics. Here
43 * rs = rangestat_arg */
44
45 // rangestat_arg.
46 enum RangeStat {
47 RS_minmax, ///< [min - rs*(max-min), max + rs*(max-min)]
48 RS_meanstd, ///< [mean - std * rs, mean + std * rs]
49 RS_quantiles, ///< [Q(rs), Q(1-rs)]
50 RS_optim, ///< alternate optimization of reconstruction error
51 };
52
53 RangeStat rangestat;
54 float rangestat_arg;
55
56 /// dimension of input vectors
57 size_t d;
58
59 /// bytes per vector
60 size_t code_size;
61
62 /// trained values (including the range)
63 std::vector<float> trained;
64
65 ScalarQuantizer (size_t d, QuantizerType qtype);
66 ScalarQuantizer ();
67
68 void train (size_t n, const float *x);
69
70
71 /// same as compute_code for several vectors
72 void compute_codes (const float * x,
73 uint8_t * codes,
74 size_t n) const ;
75
76 /// decode a vector from a given code (or n vectors if third argument)
77 void decode (const uint8_t *code, float *x, size_t n) const;
78
79 // fast, non thread-safe way of computing vector-to-code and
80 // code-to-code distances.
81 struct DistanceComputer {
82
83 /// vector-to-code distance computation
84 virtual float compute_distance (const float *x,
85 const uint8_t *code) = 0;
86
87 /// code-to-code distance computation
88 virtual float compute_code_distance (const uint8_t *code1,
89 const uint8_t *code2) = 0;
90 virtual ~DistanceComputer () {}
91 };
92
93 DistanceComputer *get_distance_computer (MetricType metric = METRIC_L2)
94 const;
95
96 };
97
98
99 struct IndexScalarQuantizer: Index {
100 /// Used to encode the vectors
101 ScalarQuantizer sq;
102
103 /// Codes. Size ntotal * pq.code_size
104 std::vector<uint8_t> codes;
105
106 size_t code_size;
107
108 /** Constructor.
109 *
110 * @param d dimensionality of the input vectors
111 * @param M number of subquantizers
112 * @param nbits number of bit per subvector index
113 */
114 IndexScalarQuantizer (int d,
115 ScalarQuantizer::QuantizerType qtype,
116 MetricType metric = METRIC_L2);
117
118 IndexScalarQuantizer ();
119
120 void train(idx_t n, const float* x) override;
121
122 void add(idx_t n, const float* x) override;
123
124 void search(
125 idx_t n,
126 const float* x,
127 idx_t k,
128 float* distances,
129 idx_t* labels) const override;
130
131 void reset() override;
132
133 void reconstruct_n(idx_t i0, idx_t ni, float* recons) const override;
134
135 void reconstruct(idx_t key, float* recons) const override;
136
137 };
138
139
140 /** An IVF implementation where the components of the residuals are
141 * encoded with a scalar uniform quantizer. All distance computations
142 * are asymmetric, so the encoded vectors are decoded and approximate
143 * distances are computed.
144 */
145
146 struct IndexIVFScalarQuantizer: IndexIVF {
147 ScalarQuantizer sq;
148
149 IndexIVFScalarQuantizer(Index *quantizer, size_t d, size_t nlist,
150 ScalarQuantizer::QuantizerType qtype,
151 MetricType metric = METRIC_L2);
152
153 IndexIVFScalarQuantizer();
154
155 void train_residual(idx_t n, const float* x) override;
156
157 void add_with_ids(idx_t n, const float* x, const long* xids) override;
158
159 void search_preassigned (idx_t n, const float *x, idx_t k,
160 const idx_t *assign,
161 const float *centroid_dis,
162 float *distances, idx_t *labels,
163 bool store_pairs) const override;
164
165 void reconstruct_from_offset (long list_no, long offset,
166 float* recons) const override;
167
168 };
169
170
171 }
172
173
174 #endif
faiss::IndexIVF
Definition: IndexIVF.h:77
faiss::ScalarQuantizer::code_size
size_t code_size
bytes per vector
Definition: IndexScalarQuantizer.h:60
faiss::ScalarQuantizer::QuantizerType
QuantizerType
Definition: IndexScalarQuantizer.h:32
faiss::IndexScalarQuantizer::search
void search(idx_t n, const float *x, idx_t k, float *distances, idx_t *labels) const override
Definition: IndexScalarQuantizer.cpp:870
faiss::IndexIVFScalarQuantizer::train_residual
void train_residual(idx_t n, const float *x) override
Definition: IndexScalarQuantizer.cpp:925
faiss::ScalarQuantizer::RS_optim
alternate optimization of reconstruction error
Definition: IndexScalarQuantizer.h:50
faiss::IndexScalarQuantizer
Definition: IndexScalarQuantizer.h:99
faiss::ScalarQuantizer::QT_8bit_uniform
same, shared range for all dimensions
Definition: IndexScalarQuantizer.h:35
faiss::IndexIVFScalarQuantizer::reconstruct_from_offset
void reconstruct_from_offset(long list_no, long offset, float *recons) const override
Definition: IndexScalarQuantizer.cpp:1113
faiss::IndexScalarQuantizer::add
void add(idx_t n, const float *x) override
Definition: IndexScalarQuantizer.cpp:815
faiss::ScalarQuantizer::DistanceComputer::compute_code_distance
virtual float compute_code_distance(const uint8_t *code1, const uint8_t *code2)=0
code-to-code distance computation
faiss::ScalarQuantizer::QT_4bit
4 bits per component
Definition: IndexScalarQuantizer.h:34
faiss::Index::assign
void assign(idx_t n, const float *x, idx_t *labels, idx_t k=1)
Definition: Index.cpp:34
faiss::IndexScalarQuantizer::reset
void reset() override
removes all elements from the database.
Definition: IndexScalarQuantizer.cpp:885
faiss::ScalarQuantizer
Definition: IndexScalarQuantizer.h:30
faiss::IndexIVFScalarQuantizer::add_with_ids
void add_with_ids(idx_t n, const float *x, const long *xids) override
Definition: IndexScalarQuantizer.cpp:944
faiss::Index::d
int d
vector dimension
Definition: Index.h:64
faiss::IndexScalarQuantizer::codes
std::vector< uint8_t > codes
Codes. Size ntotal * pq.code_size.
Definition: IndexScalarQuantizer.h:104
faiss::ScalarQuantizer::DistanceComputer
Definition: IndexScalarQuantizer.h:81
faiss::IndexScalarQuantizer::sq
ScalarQuantizer sq
Used to encode the vectors.
Definition: IndexScalarQuantizer.h:101
faiss::Index::idx_t
long idx_t
all indices are this type
Definition: Index.h:62
faiss::ScalarQuantizer::RangeStat
RangeStat
Definition: IndexScalarQuantizer.h:46
faiss::IndexIVFScalarQuantizer
Definition: IndexScalarQuantizer.h:146
faiss::ScalarQuantizer::RS_quantiles
[Q(rs), Q(1-rs)]
Definition: IndexScalarQuantizer.h:49
faiss::IndexIVFScalarQuantizer::search_preassigned
void search_preassigned(idx_t n, const float *x, idx_t k, const idx_t *assign, const float *centroid_dis, float *distances, idx_t *labels, bool store_pairs) const override
Definition: IndexScalarQuantizer.cpp:1073
faiss::ScalarQuantizer::RS_meanstd
[mean - std * rs, mean + std * rs]
Definition: IndexScalarQuantizer.h:48
faiss::ScalarQuantizer::decode
void decode(const uint8_t *code, float *x, size_t n) const
decode a vector from a given code (or n vectors if third argument)
Definition: IndexScalarQuantizer.cpp:768
faiss::ScalarQuantizer::compute_codes
void compute_codes(const float *x, uint8_t *codes, size_t n) const
same as compute_code for several vectors
Definition: IndexScalarQuantizer.cpp:757
faiss::ScalarQuantizer::QT_8bit
8 bits per component
Definition: IndexScalarQuantizer.h:33
faiss::Index
Definition: Index.h:60
faiss::IndexScalarQuantizer::reconstruct_n
void reconstruct_n(idx_t i0, idx_t ni, float *recons) const override
Definition: IndexScalarQuantizer.cpp:891
faiss::IndexScalarQuantizer::reconstruct
void reconstruct(idx_t key, float *recons) const override
Definition: IndexScalarQuantizer.cpp:901
faiss::ScalarQuantizer::RS_minmax
[min - rs*(max-min), max + rs*(max-min)]
Definition: IndexScalarQuantizer.h:47
faiss::ScalarQuantizer::trained
std::vector< float > trained
trained values (including the range)
Definition: IndexScalarQuantizer.h:63
faiss::Level1Quantizer::quantizer
Index * quantizer
quantizer that maps vectors to inverted lists
Definition: IndexIVF.h:33
faiss::IndexScalarQuantizer::train
void train(idx_t n, const float *x) override
Definition: IndexScalarQuantizer.cpp:809
faiss::ScalarQuantizer::d
size_t d
dimension of input vectors
Definition: IndexScalarQuantizer.h:57
faiss::Level1Quantizer::nlist
size_t nlist
number of possible key values
Definition: IndexIVF.h:34
faiss::MetricType
MetricType
Some algorithms support both an inner product version and a L2 search version.
Definition: Index.h:43
faiss::ScalarQuantizer::DistanceComputer::compute_distance
virtual float compute_distance(const float *x, const uint8_t *code)=0
vector-to-code distance computation