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StaticUtils.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
10 #pragma once
11
12 #include <cuda.h>
13
14 namespace faiss { namespace gpu { namespace utils {
15
16 template <typename U, typename V>
17 constexpr __host__ __device__ auto divUp(U a, V b) -> decltype(a + b) {
18 return (a + b - 1) / b;
19 }
20
21 template <typename U, typename V>
22 constexpr __host__ __device__ auto roundDown(U a, V b) -> decltype(a + b) {
23 return (a / b) * b;
24 }
25
26 template <typename U, typename V>
27 constexpr __host__ __device__ auto roundUp(U a, V b) -> decltype(a + b) {
28 return divUp(a, b) * b;
29 }
30
31 template <class T>
32 constexpr __host__ __device__ T pow(T n, T power) {
33 return (power > 0 ? n * pow(n, power - 1) : 1);
34 }
35
36 template <class T>
37 constexpr __host__ __device__ T pow2(T n) {
38 return pow(2, (T) n);
39 }
40
41 static_assert(pow2(8) == 256, "pow2");
42
43 template <typename T>
44 constexpr __host__ __device__ int log2(T n, int p = 0) {
45 return (n <= 1) ? p : log2(n / 2, p + 1);
46 }
47
48 static_assert(log2(2) == 1, "log2");
49 static_assert(log2(3) == 1, "log2");
50 static_assert(log2(4) == 2, "log2");
51
52 template <typename T>
53 constexpr __host__ __device__ bool isPowerOf2(T v) {
54 return (v && !(v & (v - 1)));
55 }
56
57 static_assert(isPowerOf2(2048), "isPowerOf2");
58 static_assert(!isPowerOf2(3333), "isPowerOf2");
59
60 template <typename T>
61 constexpr __host__ __device__ T nextHighestPowerOf2(T v) {
62 return (isPowerOf2(v) ? (T) 2 * v : ((T) 1 << (log2(v) + 1)));
63 }
64
65 static_assert(nextHighestPowerOf2(1) == 2, "nextHighestPowerOf2");
66 static_assert(nextHighestPowerOf2(2) == 4, "nextHighestPowerOf2");
67 static_assert(nextHighestPowerOf2(3) == 4, "nextHighestPowerOf2");
68 static_assert(nextHighestPowerOf2(4) == 8, "nextHighestPowerOf2");
69
70 static_assert(nextHighestPowerOf2(15) == 16, "nextHighestPowerOf2");
71 static_assert(nextHighestPowerOf2(16) == 32, "nextHighestPowerOf2");
72 static_assert(nextHighestPowerOf2(17) == 32, "nextHighestPowerOf2");
73
74 static_assert(nextHighestPowerOf2(1536000000u) == 2147483648u,
75 "nextHighestPowerOf2");
76 static_assert(nextHighestPowerOf2((size_t) 2147483648ULL) ==
77 (size_t) 4294967296ULL, "nextHighestPowerOf2");
78
79 } } } // namespace