src/core/util/useful.h

//
//
// Copyright 2015 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//

#ifndef GRPC_SRC_CORE_UTIL_USEFUL_H
#define GRPC_SRC_CORE_UTIL_USEFUL_H

#include <grpc/support/port_platform.h>

#include <cstddef>

#include "absl/strings/string_view.h"
#include "absl/types/variant.h"

/// useful utilities that don't belong anywhere else

namespace grpc_core {

template <typename T>
T Clamp(T val, T min, T max) {
  if (val < min) return min;
  if (max < val) return max;
  return val;
}

/// rotl, rotr assume x is unsigned
template <typename T>
constexpr T RotateLeft(T x, T n) {
  return ((x << n) | (x >> (sizeof(x) * 8 - n)));
}
template <typename T>
constexpr T RotateRight(T x, T n) {
  return ((x >> n) | (x << (sizeof(x) * 8 - n)));
}

// Set the n-th bit of i
template <typename T>
T SetBit(T* i, size_t n) {
  return *i |= (T(1) << n);
}

// Clear the n-th bit of i
template <typename T>
T ClearBit(T* i, size_t n) {
  return *i &= ~(T(1) << n);
}

// Get the n-th bit of i
template <typename T>
bool GetBit(T i, size_t n) {
  return (i & (T(1) << n)) != 0;
}

namespace useful_detail {
inline constexpr uint32_t HexdigitBitcount(uint32_t x) {
  return (x - ((x >> 1) & 0x77777777) - ((x >> 2) & 0x33333333) -
          ((x >> 3) & 0x11111111));
}
}  // namespace useful_detail

inline constexpr uint32_t BitCount(uint32_t i) {
  return (((useful_detail::HexdigitBitcount(i) +
            (useful_detail::HexdigitBitcount(i) >> 4)) &
           0x0f0f0f0f) %
          255);
}

inline constexpr uint32_t BitCount(uint64_t i) {
  return BitCount(static_cast<uint32_t>(i)) +
         BitCount(static_cast<uint32_t>(i >> 32));
}

inline constexpr uint32_t BitCount(uint16_t i) {
  return BitCount(static_cast<uint32_t>(i));
}
inline constexpr uint32_t BitCount(uint8_t i) {
  return BitCount(static_cast<uint32_t>(i));
}
inline constexpr uint32_t BitCount(int64_t i) {
  return BitCount(static_cast<uint64_t>(i));
}
inline constexpr uint32_t BitCount(int32_t i) {
  return BitCount(static_cast<uint32_t>(i));
}
inline constexpr uint32_t BitCount(int16_t i) {
  return BitCount(static_cast<uint16_t>(i));
}
inline constexpr uint32_t BitCount(int8_t i) {
  return BitCount(static_cast<uint8_t>(i));
}

// This function uses operator< to implement a qsort-style comparison, whereby:
// if a is smaller than b, a number smaller than 0 is returned.
// if a is bigger than b, a number greater than 0 is returned.
// if a is neither smaller nor bigger than b, 0 is returned.
template <typename T>
int QsortCompare(const T& a, const T& b) {
  if (a < b) return -1;
  if (b < a) return 1;
  return 0;
}

template <typename... X>
int QsortCompare(const absl::variant<X...>& a, const absl::variant<X...>& b) {
  const int index = QsortCompare(a.index(), b.index());
  if (index != 0) return index;
  return absl::visit(
      [&](const auto& x) {
        return QsortCompare(x, absl::get<absl::remove_cvref_t<decltype(x)>>(b));
      },
      a);
}

inline int QsortCompare(absl::string_view a, absl::string_view b) {
  return a.compare(b);
}

inline int QsortCompare(const std::string& a, const std::string& b) {
  return a.compare(b);
}

template <typename A, typename B>
int QsortCompare(const std::pair<A, B>& a, const std::pair<A, B>& b) {
  const int first = QsortCompare(a.first, b.first);
  if (first != 0) return first;
  return QsortCompare(a.second, b.second);
}

template <typename T>
constexpr size_t HashPointer(T* p, size_t range) {
  return (((reinterpret_cast<size_t>(p)) >> 4) ^
          ((reinterpret_cast<size_t>(p)) >> 9) ^
          ((reinterpret_cast<size_t>(p)) >> 14)) %
         range;
}

// Compute a+b.
// If the result is greater than INT64_MAX, return INT64_MAX.
// If the result is less than INT64_MIN, return INT64_MIN.
inline int64_t SaturatingAdd(int64_t a, int64_t b) {
  if (a > 0) {
    if (b > INT64_MAX - a) {
      return INT64_MAX;
    }
  } else if (b < INT64_MIN - a) {
    return INT64_MIN;
  }
  return a + b;
}

inline uint32_t MixHash32(uint32_t a, uint32_t b) {
  return RotateLeft(a, 2u) ^ b;
}

inline uint32_t RoundUpToPowerOf2(uint32_t v) {
  v--;
  v |= v >> 1;
  v |= v >> 2;
  v |= v >> 4;
  v |= v >> 8;
  v |= v >> 16;
  v++;
  return v;
}

}  // namespace grpc_core

#define GPR_ARRAY_SIZE(array) (sizeof(array) / sizeof(*(array)))

#endif  // GRPC_SRC_CORE_UTIL_USEFUL_H