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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 // Copyright 2004-present Facebook. All Rights Reserved.
10
11 #pragma once
12
13 #include <cuda.h>
14
15 namespace faiss { namespace gpu { namespace utils {
16
17 template <typename U, typename V>
18 constexpr __host__ __device__ auto divUp(U a, V b) -> decltype(a + b) {
19 return (a + b - 1) / b;
20 }
21
22 template <typename U, typename V>
23 constexpr __host__ __device__ auto roundDown(U a, V b) -> decltype(a + b) {
24 return (a / b) * b;
25 }
26
27 template <typename U, typename V>
28 constexpr __host__ __device__ auto roundUp(U a, V b) -> decltype(a + b) {
29 return divUp(a, b) * b;
30 }
31
32 template <class T>
33 constexpr __host__ __device__ T pow(T n, T power) {
34 return (power > 0 ? n * pow(n, power - 1) : 1);
35 }
36
37 template <class T>
38 constexpr __host__ __device__ T pow2(T n) {
39 return pow(2, (T) n);
40 }
41
42 static_assert(pow2(8) == 256, "pow2");
43
44 template <typename T>
45 constexpr __host__ __device__ int log2(T n, int p = 0) {
46 return (n <= 1) ? p : log2(n / 2, p + 1);
47 }
48
49 static_assert(log2(2) == 1, "log2");
50 static_assert(log2(3) == 1, "log2");
51 static_assert(log2(4) == 2, "log2");
52
53 template <typename T>
54 constexpr __host__ __device__ bool isPowerOf2(T v) {
55 return (v && !(v & (v - 1)));
56 }
57
58 static_assert(isPowerOf2(2048), "isPowerOf2");
59 static_assert(!isPowerOf2(3333), "isPowerOf2");
60
61 template <typename T>
62 constexpr __host__ __device__ T nextHighestPowerOf2(T v) {
63 return (isPowerOf2(v) ? (T) 2 * v : ((T) 1 << (log2(v) + 1)));
64 }
65
66 static_assert(nextHighestPowerOf2(1) == 2, "nextHighestPowerOf2");
67 static_assert(nextHighestPowerOf2(2) == 4, "nextHighestPowerOf2");
68 static_assert(nextHighestPowerOf2(3) == 4, "nextHighestPowerOf2");
69 static_assert(nextHighestPowerOf2(4) == 8, "nextHighestPowerOf2");
70
71 static_assert(nextHighestPowerOf2(15) == 16, "nextHighestPowerOf2");
72 static_assert(nextHighestPowerOf2(16) == 32, "nextHighestPowerOf2");
73 static_assert(nextHighestPowerOf2(17) == 32, "nextHighestPowerOf2");
74
75 static_assert(nextHighestPowerOf2(1536000000u) == 2147483648u,
76 "nextHighestPowerOf2");
77 static_assert(nextHighestPowerOf2((size_t) 2147483648ULL) ==
78 (size_t) 4294967296ULL, "nextHighestPowerOf2");
79
80 } } } // namespace