1 // Copyright 2015 The Gemmlowp Authors. All Rights Reserved.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 // kernel.h: general definitions for kernels.
16
17 #ifndef GEMMLOWP_INTERNAL_KERNEL_H_
18 #define GEMMLOWP_INTERNAL_KERNEL_H_
19
20 #include "../public/bit_depth.h"
21 #include "common.h"
22
23 namespace gemmlowp {
24
25 // Explanation of general gemmlowp terminology
26 // ===========================================
27 //
28 // We use the following abbreviations:
29 // LHS = "left-hand side"
30 // RHS = "right-hand side"
31 // Sometimes when referring to either LHS or RHS, we just say a "Side".
32 //
33 // In a matrix product of a MxK matrix times a KxN matrix,
34 // we call K the 'depth'. Note that M is the number of rows
35 // of the result (and of the LHS), and N is the number of columns
36 // of the result (and of the RHS).
37 //
38 // In each of the LHS and RHS matrices, we call 'width' the
39 // other dimension, besides the depth. So in the LHS, 'width'
40 // is the number of rows, while in the RHS, 'width' is the number
41 // of columns.
42 //
43 // So in the LHS MxK matrix, the depth is K and the width in M.
44 // And in the RHS KxN matrix, the depth is K and the width in N.
45 //
46 // This is illustrated in this picture:
47 //
48 // RHS width
49 // <----------------->
50 // +-----------------+ ^
51 // | RHS | | Depth
52 // +-----------------+ v
53 // ^ +--+ +-----------------+
54 // | |L | | |
55 // LHS width | |H | | Result |
56 // | |S | | |
57 // v +--+ +-----------------+
58 // <-->
59 // Depth
60
61 // Explanation of gemmlowp kernel formats and "cells"
62 // ==================================================
63 //
64 // Kernels operate on small LHS and RHS blocks that fit in registers.
65 // These blocks are stored contiguously in memory, but not always
66 // in a traditional column-major or row-major order; instead,
67 // they consist of a number of sub-blocks, which we call "cells",
68 // that are stored in column-major or row-major order. However,
69 // what really matters to us is not so much rows vs columns, but
70 // rather width vs depth. So we refer to "width-major" and "depth-major"
71 // storage orders. In the LHS, width-major means row-major,
72 // while in the RHS, width-major means column-major.
73 // There is also a third possibility, "diagonal order",
74 // which is unused at the moment.
75 //
76 // We aim to treat both sides, LHS and RHS, on an equal footing,
77 // so we call them both 'sides'. A KernelFormat thus is just a pair
78 // of KernelSideFormat's, one for LHS and one for RHS; each KernelSideFormat
79 // contains a CellFormat and a number of cells; cells are only ever
80 // stacked in the width dimension, which means stacked vertically in the
81 // LHS and stacked horizondally in the RHS.
82 //
83 // Example
84 // =======
85 //
86 // Let's work out the data layout expected by a kernel having the
87 // following format (the struct names here are defined below in this file):
88 //
89 // KernelFormat<
90 // KernelSideFormat<CellFormat<3, 4>, 3>,
91 // KernelSideFormat<CellFormat<5, 4>, 2>
92 // >
93 //
94 // The LHS format, KernelSideFormat<CellFormat<3, 4>, 3>, means:
95 // 3 cells, each cell having dimensions (width=3, depth=4), laid out in
96 // DepthMajor order (the default value, see CellFormat). In the LHS,
97 // DepthMajor means column-major, so the LHS cells are of size 3x4 in
98 // column-major order, so the LHS layout is:
99 //
100 // 0 3 6 9
101 // 1 4 7 10
102 // 2 5 8 11
103 // 12 15 18 21
104 // 13 16 19 22
105 // 14 17 20 23
106 // 24 27 30 33
107 // 25 28 31 34
108 // 26 29 32 35
109 //
110 // The RHS format, KernelSideFormat<CellFormat<5, 4>, 2>, means:
111 // 2 cells each having dimensions (width=5, depth=4), laid out in
112 // DepthMajor order (the default value, see CellFormat). In the RHS,
113 // DepthMajor means row-major, so the RHS cells are of size 4x5 in
114 // row-major order, so the RHS layout is:
115 //
116 // 0 1 2 3 4 20 21 22 23 24
117 // 5 6 7 8 9 25 26 27 28 29
118 // 10 11 12 13 14 30 31 32 33 34
119 // 15 16 17 18 19 35 36 37 38 39
120
121 // CellOrder enumerates the possible storage orders (=layouts) for
122 // a cell (see explanation above).
123 enum class CellOrder { DepthMajor, WidthMajor, Diagonal };
124
125 // CellFormat describes how data is laid
126 // out in a cell. That is, a CellOrder together with actual dimensions.
127 template <int tWidth, int tDepth, CellOrder tOrder = CellOrder::DepthMajor>
128 struct CellFormat {
129 static const int kWidth = tWidth;
130 static const int kDepth = tDepth;
131 static const CellOrder kOrder = tOrder;
132
133 static const int kSize = kWidth * kDepth;
134 };
135
136 // KernelSideFormat describes how data is laid out in a kernel side
137 // (i.e. LHS or RHS). That is, a CellFormat together with a number of
138 // cells. These cells are always stacked in the Width dimension.
139 // For example, in the LHS case, the Width dimension is the rows dimension,
140 // se we're saying that in the LHS, cells are stacked vertically.
141 // We never stack cells in the Depth dimension.
142 template <typename tCellFormat, int tCells>
143 struct KernelSideFormat {
144 typedef tCellFormat Cell;
145 static const int kCells = tCells;
146 static const int kWidth = kCells * Cell::kWidth;
147 static const int kDepth = Cell::kDepth;
148 typedef std::uint8_t Scalar;
149 };
150
151 template <typename tCellFormat, int tCells>
152 struct KernelSideFormatInt8 : KernelSideFormat<tCellFormat, tCells> {
153 typedef std::int8_t Scalar;
154 };
155
156 // KernelFormat describes fully the input data layout that a kernel expects.
157 // It consists of two KernelSideFormat's, one for LHS and one for RHS.
158 template <typename tLhs, typename tRhs>
159 struct KernelFormat {
160 typedef tLhs Lhs;
161 typedef tRhs Rhs;
162
163 static_assert(Lhs::Cell::kDepth == Rhs::Cell::kDepth, "");
164 static const int kDepth = Lhs::Cell::kDepth;
165 static const int kRows = Lhs::Cell::kWidth * Lhs::kCells;
166 static const int kCols = Rhs::Cell::kWidth * Rhs::kCells;
167 };
168
CellOrderName(CellOrder o)169 inline const char* CellOrderName(CellOrder o) {
170 switch (o) {
171 case CellOrder::DepthMajor:
172 return "DepthMajor";
173 case CellOrder::WidthMajor:
174 return "WidthMajor";
175 case CellOrder::Diagonal:
176 return "Diagonal";
177 default:
178 assert(false);
179 return nullptr;
180 }
181 }
182
183 // Returns the offset into a cell, at which a given coefficient is stored.
184 template <typename CellFormat>
OffsetIntoCell(int w,int d)185 inline int OffsetIntoCell(int w, int d) {
186 const int size = CellFormat::kWidth;
187 switch (CellFormat::kOrder) {
188 case CellOrder::DepthMajor:
189 return w + d * CellFormat::kWidth;
190 case CellOrder::WidthMajor:
191 return d + w * CellFormat::kDepth;
192 case CellOrder::Diagonal:
193 assert(CellFormat::kWidth == CellFormat::kDepth);
194 return ((size + w - d) * size + d) % (size * size);
195 default:
196 assert(false);
197 return 0;
198 }
199 }
200
201 // KernelBase is the virtual base class below all kernels.
202 // The idea is that we don't need to templatize all our code on the exact
203 // kernel type; we only need to templatize on kernel format. Kernels
204 // sharing the same format can thus share the same packing/unpacking code.
205 struct KernelBase {
206 virtual const char* Name() const = 0;
207
208 // This is the kernel implementation. We use the word 'run' consistently
209 // throughout gemmlowp to mean an inner loop, the implementation of which
210 // is to be provided by a separate optimized function.
211 virtual void Run(std::int32_t* dst_ptr, std::size_t dst_row_stride,
212 std::size_t dst_col_stride, const std::uint8_t* lhs_ptr,
213 const std::uint8_t* rhs_ptr, std::size_t start_depth,
214 std::size_t run_depth) const = 0;
215
~KernelBaseKernelBase216 virtual ~KernelBase() {}
217 };
218
219 template <typename KernelScalarType>
220 struct ZeroPointInputValue {};
221
222 template <>
223 struct ZeroPointInputValue<std::uint8_t> {
224 static constexpr std::uint8_t kValue = 0;
225 };
226
227 template <>
228 struct ZeroPointInputValue<std::int8_t> {
229 static constexpr std::uint8_t kValue = 128;
230 };
231
232 } // namespace gemmlowp
233
234 #endif // GEMMLOWP_INTERNAL_KERNEL_H_
235