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/*
* Copyright (C) 2015 The Android Open Source Project
*
* 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 ART_RUNTIME_BASE_BIT_UTILS_H_
#define ART_RUNTIME_BASE_BIT_UTILS_H_
#include <iterator>
#include <limits>
#include <type_traits>
#include "base/logging.h"
#include "base/iteration_range.h"
namespace art {
template<typename T>
static constexpr int CLZ(T x) {
static_assert(std::is_integral<T>::value, "T must be integral");
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
static_assert(sizeof(T) <= sizeof(long long), // NOLINT [runtime/int] [4]
"T too large, must be smaller than long long");
return
DCHECK_CONSTEXPR(x != 0, "x must not be zero", T(0))
(sizeof(T) == sizeof(uint32_t))
? __builtin_clz(x)
: __builtin_clzll(x);
}
template<typename T>
static constexpr int CTZ(T x) {
static_assert(std::is_integral<T>::value, "T must be integral");
// It is not unreasonable to ask for trailing zeros in a negative number. As such, do not check
// that T is an unsigned type.
static_assert(sizeof(T) <= sizeof(long long), // NOLINT [runtime/int] [4]
"T too large, must be smaller than long long");
return
DCHECK_CONSTEXPR(x != 0, "x must not be zero", T(0))
(sizeof(T) == sizeof(uint32_t))
? __builtin_ctz(x)
: __builtin_ctzll(x);
}
// Return the number of 1-bits in `x`.
template<typename T>
static constexpr int POPCOUNT(T x) {
return (sizeof(T) == sizeof(uint32_t))
? __builtin_popcount(x)
: __builtin_popcountll(x);
}
// Find the bit position of the most significant bit (0-based), or -1 if there were no bits set.
template <typename T>
static constexpr ssize_t MostSignificantBit(T value) {
static_assert(std::is_integral<T>::value, "T must be integral");
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
static_assert(std::numeric_limits<T>::radix == 2, "Unexpected radix!");
return (value == 0) ? -1 : std::numeric_limits<T>::digits - 1 - CLZ(value);
}
// Find the bit position of the least significant bit (0-based), or -1 if there were no bits set.
template <typename T>
static constexpr ssize_t LeastSignificantBit(T value) {
static_assert(std::is_integral<T>::value, "T must be integral");
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
return (value == 0) ? -1 : CTZ(value);
}
// How many bits (minimally) does it take to store the constant 'value'? i.e. 1 for 1, 3 for 5, etc.
template <typename T>
static constexpr size_t MinimumBitsToStore(T value) {
return static_cast<size_t>(MostSignificantBit(value) + 1);
}
template <typename T>
static constexpr inline T RoundUpToPowerOfTwo(T x) {
static_assert(std::is_integral<T>::value, "T must be integral");
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
// NOTE: Undefined if x > (1 << (std::numeric_limits<T>::digits - 1)).
return (x < 2u) ? x : static_cast<T>(1u) << (std::numeric_limits<T>::digits - CLZ(x - 1u));
}
template<typename T>
static constexpr bool IsPowerOfTwo(T x) {
static_assert(std::is_integral<T>::value, "T must be integral");
// TODO: assert unsigned. There is currently many uses with signed values.
return (x & (x - 1)) == 0;
}
template<typename T>
static inline int WhichPowerOf2(T x) {
static_assert(std::is_integral<T>::value, "T must be integral");
// TODO: assert unsigned. There is currently many uses with signed values.
DCHECK((x != 0) && IsPowerOfTwo(x));
return CTZ(x);
}
// For rounding integers.
// NOTE: In the absence of std::omit_from_type_deduction<T> or std::identity<T>, use std::decay<T>.
template<typename T>
static constexpr T RoundDown(T x, typename std::decay<T>::type n) WARN_UNUSED;
template<typename T>
static constexpr T RoundDown(T x, typename std::decay<T>::type n) {
return
DCHECK_CONSTEXPR(IsPowerOfTwo(n), , T(0))
(x & -n);
}
template<typename T>
static constexpr T RoundUp(T x, typename std::remove_reference<T>::type n) WARN_UNUSED;
template<typename T>
static constexpr T RoundUp(T x, typename std::remove_reference<T>::type n) {
return RoundDown(x + n - 1, n);
}
// For aligning pointers.
template<typename T>
static inline T* AlignDown(T* x, uintptr_t n) WARN_UNUSED;
template<typename T>
static inline T* AlignDown(T* x, uintptr_t n) {
return reinterpret_cast<T*>(RoundDown(reinterpret_cast<uintptr_t>(x), n));
}
template<typename T>
static inline T* AlignUp(T* x, uintptr_t n) WARN_UNUSED;
template<typename T>
static inline T* AlignUp(T* x, uintptr_t n) {
return reinterpret_cast<T*>(RoundUp(reinterpret_cast<uintptr_t>(x), n));
}
template<int n, typename T>
static constexpr bool IsAligned(T x) {
static_assert((n & (n - 1)) == 0, "n is not a power of two");
return (x & (n - 1)) == 0;
}
template<int n, typename T>
static inline bool IsAligned(T* x) {
return IsAligned<n>(reinterpret_cast<const uintptr_t>(x));
}
template<typename T>
static inline bool IsAlignedParam(T x, int n) {
return (x & (n - 1)) == 0;
}
#define CHECK_ALIGNED(value, alignment) \
CHECK(::art::IsAligned<alignment>(value)) << reinterpret_cast<const void*>(value)
#define DCHECK_ALIGNED(value, alignment) \
DCHECK(::art::IsAligned<alignment>(value)) << reinterpret_cast<const void*>(value)
#define CHECK_ALIGNED_PARAM(value, alignment) \
CHECK(::art::IsAlignedParam(value, alignment)) << reinterpret_cast<const void*>(value)
#define DCHECK_ALIGNED_PARAM(value, alignment) \
DCHECK(::art::IsAlignedParam(value, alignment)) << reinterpret_cast<const void*>(value)
// Like sizeof, but count how many bits a type takes. Pass type explicitly.
template <typename T>
static constexpr size_t BitSizeOf() {
static_assert(std::is_integral<T>::value, "T must be integral");
typedef typename std::make_unsigned<T>::type unsigned_type;
static_assert(sizeof(T) == sizeof(unsigned_type), "Unexpected type size mismatch!");
static_assert(std::numeric_limits<unsigned_type>::radix == 2, "Unexpected radix!");
return std::numeric_limits<unsigned_type>::digits;
}
// Like sizeof, but count how many bits a type takes. Infers type from parameter.
template <typename T>
static constexpr size_t BitSizeOf(T /*x*/) {
return BitSizeOf<T>();
}
static inline uint16_t Low16Bits(uint32_t value) {
return static_cast<uint16_t>(value);
}
static inline uint16_t High16Bits(uint32_t value) {
return static_cast<uint16_t>(value >> 16);
}
static inline uint32_t Low32Bits(uint64_t value) {
return static_cast<uint32_t>(value);
}
static inline uint32_t High32Bits(uint64_t value) {
return static_cast<uint32_t>(value >> 32);
}
// Check whether an N-bit two's-complement representation can hold value.
template <typename T>
static inline bool IsInt(size_t N, T value) {
if (N == BitSizeOf<T>()) {
return true;
} else {
CHECK_LT(0u, N);
CHECK_LT(N, BitSizeOf<T>());
T limit = static_cast<T>(1) << (N - 1u);
return (-limit <= value) && (value < limit);
}
}
template <typename T>
static constexpr T GetIntLimit(size_t bits) {
return
DCHECK_CONSTEXPR(bits > 0, "bits cannot be zero", 0)
DCHECK_CONSTEXPR(bits < BitSizeOf<T>(), "kBits must be < max.", 0)
static_cast<T>(1) << (bits - 1);
}
template <size_t kBits, typename T>
static constexpr bool IsInt(T value) {
static_assert(kBits > 0, "kBits cannot be zero.");
static_assert(kBits <= BitSizeOf<T>(), "kBits must be <= max.");
static_assert(std::is_signed<T>::value, "Needs a signed type.");
// Corner case for "use all bits." Can't use the limits, as they would overflow, but it is
// trivially true.
return (kBits == BitSizeOf<T>()) ?
true :
(-GetIntLimit<T>(kBits) <= value) && (value < GetIntLimit<T>(kBits));
}
template <size_t kBits, typename T>
static constexpr bool IsUint(T value) {
static_assert(kBits > 0, "kBits cannot be zero.");
static_assert(kBits <= BitSizeOf<T>(), "kBits must be <= max.");
static_assert(std::is_integral<T>::value, "Needs an integral type.");
// Corner case for "use all bits." Can't use the limits, as they would overflow, but it is
// trivially true.
// NOTE: To avoid triggering assertion in GetIntLimit(kBits+1) if kBits+1==BitSizeOf<T>(),
// use GetIntLimit(kBits)*2u. The unsigned arithmetic works well for us if it overflows.
return (0 <= value) &&
(kBits == BitSizeOf<T>() ||
(static_cast<typename std::make_unsigned<T>::type>(value) <=
GetIntLimit<typename std::make_unsigned<T>::type>(kBits) * 2u - 1u));
}
template <size_t kBits, typename T>
static constexpr bool IsAbsoluteUint(T value) {
static_assert(kBits <= BitSizeOf<T>(), "kBits must be <= max.");
static_assert(std::is_integral<T>::value, "Needs an integral type.");
typedef typename std::make_unsigned<T>::type unsigned_type;
return (kBits == BitSizeOf<T>())
? true
: IsUint<kBits>(value < 0
? static_cast<unsigned_type>(-1 - value) + 1u // Avoid overflow.
: static_cast<unsigned_type>(value));
}
// Generate maximum/minimum values for signed/unsigned n-bit integers
template <typename T>
static constexpr T MaxInt(size_t bits) {
return
DCHECK_CONSTEXPR(bits > 0, "bits cannot be zero", 0)
DCHECK_CONSTEXPR(bits <= BitSizeOf<T>(), "kBits must be < max.", 0)
bits == BitSizeOf<T>()
? std::numeric_limits<T>::max()
: std::is_signed<T>::value
? (bits == 1
? 0
: static_cast<T>(MaxInt<typename std::make_unsigned<T>::type>(bits - 1)))
: static_cast<T>(UINT64_C(1) << bits) - static_cast<T>(1);
}
template <typename T>
static constexpr T MinInt(size_t bits) {
return
DCHECK_CONSTEXPR(bits > 0, "bits cannot be zero", 0)
DCHECK_CONSTEXPR(bits <= BitSizeOf<T>(), "kBits must be < max.", 0)
bits == BitSizeOf<T>()
? std::numeric_limits<T>::min()
: std::is_signed<T>::value
? (bits == 1 ? -1 : static_cast<T>(-1) - MaxInt<T>(bits))
: static_cast<T>(0);
}
// Using the Curiously Recurring Template Pattern to implement everything shared
// by LowToHighBitIterator and HighToLowBitIterator, i.e. everything but operator*().
template <typename T, typename Iter>
class BitIteratorBase
: public std::iterator<std::forward_iterator_tag, uint32_t, ptrdiff_t, void, void> {
static_assert(std::is_integral<T>::value, "T must be integral");
static_assert(std::is_unsigned<T>::value, "T must be unsigned");
static_assert(sizeof(T) == sizeof(uint32_t) || sizeof(T) == sizeof(uint64_t), "Unsupported size");
public:
BitIteratorBase() : bits_(0u) { }
explicit BitIteratorBase(T bits) : bits_(bits) { }
Iter& operator++() {
DCHECK_NE(bits_, 0u);
uint32_t bit = *static_cast<Iter&>(*this);
bits_ &= ~(static_cast<T>(1u) << bit);
return static_cast<Iter&>(*this);
}
Iter& operator++(int) {
Iter tmp(static_cast<Iter&>(*this));
++*this;
return tmp;
}
protected:
T bits_;
template <typename U, typename I>
friend bool operator==(const BitIteratorBase<U, I>& lhs, const BitIteratorBase<U, I>& rhs);
};
template <typename T, typename Iter>
bool operator==(const BitIteratorBase<T, Iter>& lhs, const BitIteratorBase<T, Iter>& rhs) {
return lhs.bits_ == rhs.bits_;
}
template <typename T, typename Iter>
bool operator!=(const BitIteratorBase<T, Iter>& lhs, const BitIteratorBase<T, Iter>& rhs) {
return !(lhs == rhs);
}
template <typename T>
class LowToHighBitIterator : public BitIteratorBase<T, LowToHighBitIterator<T>> {
public:
using BitIteratorBase<T, LowToHighBitIterator<T>>::BitIteratorBase;
uint32_t operator*() const {
DCHECK_NE(this->bits_, 0u);
return CTZ(this->bits_);
}
};
template <typename T>
class HighToLowBitIterator : public BitIteratorBase<T, HighToLowBitIterator<T>> {
public:
using BitIteratorBase<T, HighToLowBitIterator<T>>::BitIteratorBase;
uint32_t operator*() const {
DCHECK_NE(this->bits_, 0u);
static_assert(std::numeric_limits<T>::radix == 2, "Unexpected radix!");
return std::numeric_limits<T>::digits - 1u - CLZ(this->bits_);
}
};
template <typename T>
IterationRange<LowToHighBitIterator<T>> LowToHighBits(T bits) {
return IterationRange<LowToHighBitIterator<T>>(
LowToHighBitIterator<T>(bits), LowToHighBitIterator<T>());
}
template <typename T>
IterationRange<HighToLowBitIterator<T>> HighToLowBits(T bits) {
return IterationRange<HighToLowBitIterator<T>>(
HighToLowBitIterator<T>(bits), HighToLowBitIterator<T>());
}
} // namespace art
#endif // ART_RUNTIME_BASE_BIT_UTILS_H_