StaticUtils.h

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD+Patents license found in the
 * LICENSE file in the root directory of this source tree.
 */


#pragma once

#include <cuda.h>

namespace faiss { namespace gpu { namespace utils {

template <typename U, typename V>
constexpr __host__ __device__ auto divUp(U a, V b) -> decltype(a + b) {
  return (a + b - 1) / b;
}

template <typename U, typename V>
constexpr __host__ __device__ auto roundDown(U a, V b) -> decltype(a + b) {
  return (a / b) * b;
}

template <typename U, typename V>
constexpr __host__ __device__ auto roundUp(U a, V b) -> decltype(a + b) {
  return divUp(a, b) * b;
}

template <class T>
constexpr __host__ __device__ T pow(T n, T power) {
  return (power > 0 ? n * pow(n, power - 1) : 1);
}

template <class T>
constexpr __host__ __device__ T pow2(T n) {
  return pow(2, (T) n);
}

static_assert(pow2(8) == 256, "pow2");

template <typename T>
constexpr __host__ __device__ int log2(T n, int p = 0) {
  return (n <= 1) ? p : log2(n / 2, p + 1);
}

static_assert(log2(2) == 1, "log2");
static_assert(log2(3) == 1, "log2");
static_assert(log2(4) == 2, "log2");

template <typename T>
constexpr __host__ __device__ bool isPowerOf2(T v) {
  return (v && !(v & (v - 1)));
}

static_assert(isPowerOf2(2048), "isPowerOf2");
static_assert(!isPowerOf2(3333), "isPowerOf2");

template <typename T>
constexpr __host__ __device__ T nextHighestPowerOf2(T v) {
  return (isPowerOf2(v) ? (T) 2 * v : ((T) 1 << (log2(v) + 1)));
}

static_assert(nextHighestPowerOf2(1) == 2, "nextHighestPowerOf2");
static_assert(nextHighestPowerOf2(2) == 4, "nextHighestPowerOf2");
static_assert(nextHighestPowerOf2(3) == 4, "nextHighestPowerOf2");
static_assert(nextHighestPowerOf2(4) == 8, "nextHighestPowerOf2");

static_assert(nextHighestPowerOf2(15) == 16, "nextHighestPowerOf2");
static_assert(nextHighestPowerOf2(16) == 32, "nextHighestPowerOf2");
static_assert(nextHighestPowerOf2(17) == 32, "nextHighestPowerOf2");

static_assert(nextHighestPowerOf2(1536000000u) == 2147483648u,
              "nextHighestPowerOf2");
static_assert(nextHighestPowerOf2((size_t) 2147483648ULL) ==
              (size_t) 4294967296ULL, "nextHighestPowerOf2");

} } } // namespace