libartbase/base/bit_utils.h - LeafOS-Project/android_art - Gitiles

 /*
  * 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_LIBARTBASE_BASE_BIT_UTILS_H_
 #define ART_LIBARTBASE_BASE_BIT_UTILS_H_

 #include <limits>
 #include <type_traits>

 #include <android-base/logging.h>

 #include "stl_util_identity.h"

 namespace art {

 // Like sizeof, but count how many bits a type takes. Pass type explicitly.
 template <typename T>
 constexpr size_t BitSizeOf() {
   static_assert(std::is_integral<T>::value, "T must be integral");
   using unsigned_type = typename std::make_unsigned<T>::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>
 constexpr size_t BitSizeOf(T /*x*/) {
   return BitSizeOf<T>();
 }

 template<typename T>
 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(std::numeric_limits<T>::radix == 2, "Unexpected radix!");
   static_assert(sizeof(T) == sizeof(uint64_t) || sizeof(T) <= sizeof(uint32_t),
                 "Unsupported sizeof(T)");
   DCHECK_NE(x, 0u);
   constexpr bool is_64_bit = (sizeof(T) == sizeof(uint64_t));
   constexpr size_t adjustment =
       is_64_bit ? 0u : std::numeric_limits<uint32_t>::digits - std::numeric_limits<T>::digits;
   return is_64_bit ? __builtin_clzll(x) : __builtin_clz(x) - adjustment;
 }

 // Similar to CLZ except that on zero input it returns bitwidth and supports signed integers.
 template<typename T>
 constexpr int JAVASTYLE_CLZ(T x) {
   static_assert(std::is_integral<T>::value, "T must be integral");
   using unsigned_type = typename std::make_unsigned<T>::type;
   return (x == 0) ? BitSizeOf<T>() : CLZ(static_cast<unsigned_type>(x));
 }

 template<typename T>
 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(uint64_t) || sizeof(T) <= sizeof(uint32_t),
                 "Unsupported sizeof(T)");
   DCHECK_NE(x, static_cast<T>(0));
   return (sizeof(T) == sizeof(uint64_t)) ? __builtin_ctzll(x) : __builtin_ctz(x);
 }

 // Similar to CTZ except that on zero input it returns bitwidth and supports signed integers.
 template<typename T>
 constexpr int JAVASTYLE_CTZ(T x) {
   static_assert(std::is_integral<T>::value, "T must be integral");
   using unsigned_type = typename std::make_unsigned<T>::type;
   return (x == 0) ? BitSizeOf<T>() : CTZ(static_cast<unsigned_type>(x));
 }

 // Return the number of 1-bits in `x`.
 template<typename T>
 constexpr int POPCOUNT(T x) {
   return (sizeof(T) == sizeof(uint32_t)) ? __builtin_popcount(x) : __builtin_popcountll(x);
 }

 // Swap bytes.
 template<typename T>
 constexpr T BSWAP(T x) {
   if (sizeof(T) == sizeof(uint16_t)) {
     return __builtin_bswap16(x);
   } else if (sizeof(T) == sizeof(uint32_t)) {
     return __builtin_bswap32(x);
   } else {
     return __builtin_bswap64(x);
   }
 }

 // Find the bit position of the most significant bit (0-based), or -1 if there were no bits set.
 template <typename T>
 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>
 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>
 constexpr size_t MinimumBitsToStore(T value) {
   return static_cast<size_t>(MostSignificantBit(value) + 1);
 }

 template <typename T>
 constexpr 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));
 }

 // Return highest possible N - a power of two - such that val >= N.
 template <typename T>
 constexpr T TruncToPowerOfTwo(T val) {
   static_assert(std::is_integral<T>::value, "T must be integral");
   static_assert(std::is_unsigned<T>::value, "T must be unsigned");
   return (val != 0) ? static_cast<T>(1u) << (BitSizeOf<T>() - CLZ(val) - 1u) : 0;
 }

 template<typename T>
 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>
 constexpr 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: Omit the `n` from T type deduction, deduce only from the `x` argument.
 template<typename T>
 constexpr T RoundDown(T x, typename Identity<T>::type n) WARN_UNUSED;

 template<typename T>
 constexpr T RoundDown(T x, typename Identity<T>::type n) {
   DCHECK(IsPowerOfTwo(n));
   return (x & -n);
 }

 template<typename T>
 constexpr T RoundUp(T x, typename std::remove_reference<T>::type n) WARN_UNUSED;

 template<typename T>
 constexpr T RoundUp(T x, typename std::remove_reference<T>::type n) {
   return RoundDown(x + n - 1, n);
 }

 // For aligning pointers.
 template<typename T>
 inline T* AlignDown(T* x, uintptr_t n) WARN_UNUSED;

 template<typename T>
 inline T* AlignDown(T* x, uintptr_t n) {
   return reinterpret_cast<T*>(RoundDown(reinterpret_cast<uintptr_t>(x), n));
 }

 template<typename T>
 inline T* AlignUp(T* x, uintptr_t n) WARN_UNUSED;

 template<typename T>
 inline T* AlignUp(T* x, uintptr_t n) {
   return reinterpret_cast<T*>(RoundUp(reinterpret_cast<uintptr_t>(x), n));
 }

 template<int n, typename T>
 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>
 inline bool IsAligned(T* x) {
   return IsAligned<n>(reinterpret_cast<const uintptr_t>(x));
 }

 template<typename T>
 inline bool IsAlignedParam(T x, int n) {
   return (x & (n - 1)) == 0;
 }

 template<typename T>
 inline bool IsAlignedParam(T* x, int n) {
   return IsAlignedParam(reinterpret_cast<const uintptr_t>(x), n);
 }

 #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)

 inline uint16_t Low16Bits(uint32_t value) {
   return static_cast<uint16_t>(value);
 }

 inline uint16_t High16Bits(uint32_t value) {
   return static_cast<uint16_t>(value >> 16);
 }

 inline uint32_t Low32Bits(uint64_t value) {
   return static_cast<uint32_t>(value);
 }

 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>
 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>
 constexpr T GetIntLimit(size_t bits) {
   DCHECK_NE(bits, 0u);
   DCHECK_LT(bits, BitSizeOf<T>());
   return static_cast<T>(1) << (bits - 1);
 }

 template <size_t kBits, typename T>
 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>
 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.
   using unsigned_type = typename std::make_unsigned<T>::type;
   return (0 <= value) &&
       (kBits == BitSizeOf<T>() ||
           (static_cast<unsigned_type>(value) <= GetIntLimit<unsigned_type>(kBits) * 2u - 1u));
 }

 template <size_t kBits, typename T>
 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.");
   using unsigned_type = typename std::make_unsigned<T>::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>
 constexpr T MaxInt(size_t bits) {
   DCHECK(std::is_unsigned<T>::value || bits > 0u) << "bits cannot be zero for signed.";
   DCHECK_LE(bits, BitSizeOf<T>());
   using unsigned_type = typename std::make_unsigned<T>::type;
   return bits == BitSizeOf<T>()
       ? std::numeric_limits<T>::max()
       : std::is_signed<T>::value
           ? ((bits == 1u) ? 0 : static_cast<T>(MaxInt<unsigned_type>(bits - 1)))
           : static_cast<T>(UINT64_C(1) << bits) - static_cast<T>(1);
 }

 template <typename T>
 constexpr T MinInt(size_t bits) {
   DCHECK(std::is_unsigned<T>::value || bits > 0) << "bits cannot be zero for signed.";
   DCHECK_LE(bits, BitSizeOf<T>());
   return bits == BitSizeOf<T>()
       ? std::numeric_limits<T>::min()
       : std::is_signed<T>::value
           ? ((bits == 1u) ? -1 : static_cast<T>(-1) - MaxInt<T>(bits))
           : static_cast<T>(0);
 }

 // Returns value with bit set in lowest one-bit position or 0 if 0.  (java.lang.X.lowestOneBit).
 template <typename kind>
 inline static kind LowestOneBitValue(kind opnd) {
   // Hacker's Delight, Section 2-1
   return opnd & -opnd;
 }

 // Returns value with bit set in hightest one-bit position or 0 if 0.  (java.lang.X.highestOneBit).
 template <typename T>
 inline static T HighestOneBitValue(T opnd) {
   using unsigned_type = typename std::make_unsigned<T>::type;
   T res;
   if (opnd == 0) {
     res = 0;
   } else {
     int bit_position = BitSizeOf<T>() - (CLZ(static_cast<unsigned_type>(opnd)) + 1);
     res = static_cast<T>(UINT64_C(1) << bit_position);
   }
   return res;
 }

 // Rotate bits.
 template <typename T, bool left>
 inline static T Rot(T opnd, int distance) {
   int mask = BitSizeOf<T>() - 1;
   int unsigned_right_shift = left ? (-distance & mask) : (distance & mask);
   int signed_left_shift = left ? (distance & mask) : (-distance & mask);
   using unsigned_type = typename std::make_unsigned<T>::type;
   return (static_cast<unsigned_type>(opnd) >> unsigned_right_shift) | (opnd << signed_left_shift);
 }

 // TUNING: use rbit for arm/arm64
 inline static uint32_t ReverseBits32(uint32_t opnd) {
   // Hacker's Delight 7-1
   opnd = ((opnd >>  1) & 0x55555555) | ((opnd & 0x55555555) <<  1);
   opnd = ((opnd >>  2) & 0x33333333) | ((opnd & 0x33333333) <<  2);
   opnd = ((opnd >>  4) & 0x0F0F0F0F) | ((opnd & 0x0F0F0F0F) <<  4);
   opnd = ((opnd >>  8) & 0x00FF00FF) | ((opnd & 0x00FF00FF) <<  8);
   opnd = ((opnd >> 16)) | ((opnd) << 16);
   return opnd;
 }

 // TUNING: use rbit for arm/arm64
 inline static uint64_t ReverseBits64(uint64_t opnd) {
   // Hacker's Delight 7-1
   opnd = (opnd & 0x5555555555555555L) << 1 | ((opnd >> 1) & 0x5555555555555555L);
   opnd = (opnd & 0x3333333333333333L) << 2 | ((opnd >> 2) & 0x3333333333333333L);
   opnd = (opnd & 0x0f0f0f0f0f0f0f0fL) << 4 | ((opnd >> 4) & 0x0f0f0f0f0f0f0f0fL);
   opnd = (opnd & 0x00ff00ff00ff00ffL) << 8 | ((opnd >> 8) & 0x00ff00ff00ff00ffL);
   opnd = (opnd << 48) | ((opnd & 0xffff0000L) << 16) | ((opnd >> 16) & 0xffff0000L) | (opnd >> 48);
   return opnd;
 }

 // Create a mask for the least significant "bits"
 // The returned value is always unsigned to prevent undefined behavior for bitwise ops.
 //
 // Given 'bits',
 // Returns:
 //                   <--- bits --->
 // +-----------------+------------+
 // | 0 ............0 |   1.....1  |
 // +-----------------+------------+
 // msb                           lsb
 template <typename T = size_t>
 inline static constexpr std::make_unsigned_t<T> MaskLeastSignificant(size_t bits) {
   DCHECK_GE(BitSizeOf<T>(), bits) << "Bits out of range for type T";
   using unsigned_T = std::make_unsigned_t<T>;
   if (bits >= BitSizeOf<T>()) {
     return std::numeric_limits<unsigned_T>::max();
   } else {
     auto kOne = static_cast<unsigned_T>(1);  // Do not truncate for T>size_t.
     return static_cast<unsigned_T>((kOne << bits) - kOne);
   }
 }

 // Clears the bitfield starting at the least significant bit "lsb" with a bitwidth of 'width'.
 // (Equivalent of ARM BFC instruction).
 //
 // Given:
 //           <-- width  -->
 // +--------+------------+--------+
 // | ABC... |  bitfield  | XYZ... +
 // +--------+------------+--------+
 //                       lsb      0
 // Returns:
 //           <-- width  -->
 // +--------+------------+--------+
 // | ABC... | 0........0 | XYZ... +
 // +--------+------------+--------+
 //                       lsb      0
 template <typename T>
 inline static constexpr T BitFieldClear(T value, size_t lsb, size_t width) {
   DCHECK_GE(BitSizeOf(value), lsb + width) << "Bit field out of range for value";
   const auto val = static_cast<std::make_unsigned_t<T>>(value);
   const auto mask = MaskLeastSignificant<T>(width);

   return static_cast<T>(val & ~(mask << lsb));
 }

 // Inserts the contents of 'data' into bitfield of 'value'  starting
 // at the least significant bit "lsb" with a bitwidth of 'width'.
 // Note: data must be within range of [MinInt(width), MaxInt(width)].
 // (Equivalent of ARM BFI instruction).
 //
 // Given (data):
 //           <-- width  -->
 // +--------+------------+--------+
 // | ABC... |  bitfield  | XYZ... +
 // +--------+------------+--------+
 //                       lsb      0
 // Returns:
 //           <-- width  -->
 // +--------+------------+--------+
 // | ABC... | 0...data   | XYZ... +
 // +--------+------------+--------+
 //                       lsb      0

 template <typename T, typename T2>
 inline static constexpr T BitFieldInsert(T value, T2 data, size_t lsb, size_t width) {
   DCHECK_GE(BitSizeOf(value), lsb + width) << "Bit field out of range for value";
   if (width != 0u) {
     DCHECK_GE(MaxInt<T2>(width), data) << "Data out of range [too large] for bitwidth";
     DCHECK_LE(MinInt<T2>(width), data) << "Data out of range [too small] for bitwidth";
   } else {
     DCHECK_EQ(static_cast<T2>(0), data) << "Data out of range [nonzero] for bitwidth 0";
   }
   const auto data_mask = MaskLeastSignificant<T2>(width);
   const auto value_cleared = BitFieldClear(value, lsb, width);

   return static_cast<T>(value_cleared | ((data & data_mask) << lsb));
 }

 // Extracts the bitfield starting at the least significant bit "lsb" with a bitwidth of 'width'.
 // Signed types are sign-extended during extraction. (Equivalent of ARM UBFX/SBFX instruction).
 //
 // Given:
 //           <-- width   -->
 // +--------+-------------+-------+
 // |        |   bitfield  |       +
 // +--------+-------------+-------+
 //                       lsb      0
 // (Unsigned) Returns:
 //                  <-- width   -->
 // +----------------+-------------+
 // | 0...        0  |   bitfield  |
 // +----------------+-------------+
 //                                0
 // (Signed) Returns:
 //                  <-- width   -->
 // +----------------+-------------+
 // | S...        S  |   bitfield  |
 // +----------------+-------------+
 //                                0
 // where S is the highest bit in 'bitfield'.
 template <typename T>
 inline static constexpr T BitFieldExtract(T value, size_t lsb, size_t width) {
   DCHECK_GE(BitSizeOf(value), lsb + width) << "Bit field out of range for value";
   const auto val = static_cast<std::make_unsigned_t<T>>(value);

   const T bitfield_unsigned =
       static_cast<T>((val >> lsb) & MaskLeastSignificant<T>(width));
   if (std::is_signed<T>::value) {
     // Perform sign extension
     if (width == 0) {  // Avoid underflow.
       return static_cast<T>(0);
     } else if (bitfield_unsigned & (1 << (width - 1))) {  // Detect if sign bit was set.
       // MSB        <width> LSB
       // 0b11111...100...000000
       const auto ones_negmask = ~MaskLeastSignificant<T>(width);
       return static_cast<T>(bitfield_unsigned | ones_negmask);
     }
   }
   // Skip sign extension.
   return bitfield_unsigned;
 }

 }  // namespace art

 #endif  // ART_LIBARTBASE_BASE_BIT_UTILS_H_
	/*
	* 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_LIBARTBASE_BASE_BIT_UTILS_H_
	#define ART_LIBARTBASE_BASE_BIT_UTILS_H_

	#include <limits>
	#include <type_traits>

	#include <android-base/logging.h>

	#include "stl_util_identity.h"

	namespace art {

	// Like sizeof, but count how many bits a type takes. Pass type explicitly.
	template <typename T>
	constexpr size_t BitSizeOf() {
	static_assert(std::is_integral<T>::value, "T must be integral");
	using unsigned_type = typename std::make_unsigned<T>::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>
	constexpr size_t BitSizeOf(T /x/) {
	return BitSizeOf<T>();
	}

	template<typename T>
	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(std::numeric_limits<T>::radix == 2, "Unexpected radix!");
	static_assert(sizeof(T) == sizeof(uint64_t) \|\| sizeof(T) <= sizeof(uint32_t),
	"Unsupported sizeof(T)");
	DCHECK_NE(x, 0u);
	constexpr bool is_64_bit = (sizeof(T) == sizeof(uint64_t));
	constexpr size_t adjustment =
	is_64_bit ? 0u : std::numeric_limits<uint32_t>::digits - std::numeric_limits<T>::digits;
	return is_64_bit ? __builtin_clzll(x) : __builtin_clz(x) - adjustment;
	}

	// Similar to CLZ except that on zero input it returns bitwidth and supports signed integers.
	template<typename T>
	constexpr int JAVASTYLE_CLZ(T x) {
	static_assert(std::is_integral<T>::value, "T must be integral");
	using unsigned_type = typename std::make_unsigned<T>::type;
	return (x == 0) ? BitSizeOf<T>() : CLZ(static_cast<unsigned_type>(x));
	}

	template<typename T>
	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(uint64_t) \|\| sizeof(T) <= sizeof(uint32_t),
	"Unsupported sizeof(T)");
	DCHECK_NE(x, static_cast<T>(0));
	return (sizeof(T) == sizeof(uint64_t)) ? __builtin_ctzll(x) : __builtin_ctz(x);
	}

	// Similar to CTZ except that on zero input it returns bitwidth and supports signed integers.
	template<typename T>
	constexpr int JAVASTYLE_CTZ(T x) {
	static_assert(std::is_integral<T>::value, "T must be integral");
	using unsigned_type = typename std::make_unsigned<T>::type;
	return (x == 0) ? BitSizeOf<T>() : CTZ(static_cast<unsigned_type>(x));
	}

	// Return the number of 1-bits in `x`.
	template<typename T>
	constexpr int POPCOUNT(T x) {
	return (sizeof(T) == sizeof(uint32_t)) ? __builtin_popcount(x) : __builtin_popcountll(x);
	}

	// Swap bytes.
	template<typename T>
	constexpr T BSWAP(T x) {
	if (sizeof(T) == sizeof(uint16_t)) {
	return __builtin_bswap16(x);
	} else if (sizeof(T) == sizeof(uint32_t)) {
	return __builtin_bswap32(x);
	} else {
	return __builtin_bswap64(x);
	}
	}

	// Find the bit position of the most significant bit (0-based), or -1 if there were no bits set.
	template <typename T>
	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>
	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>
	constexpr size_t MinimumBitsToStore(T value) {
	return static_cast<size_t>(MostSignificantBit(value) + 1);
	}

	template <typename T>
	constexpr 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));
	}

	// Return highest possible N - a power of two - such that val >= N.
	template <typename T>
	constexpr T TruncToPowerOfTwo(T val) {
	static_assert(std::is_integral<T>::value, "T must be integral");
	static_assert(std::is_unsigned<T>::value, "T must be unsigned");
	return (val != 0) ? static_cast<T>(1u) << (BitSizeOf<T>() - CLZ(val) - 1u) : 0;
	}

	template<typename T>
	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>
	constexpr 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: Omit the `n` from T type deduction, deduce only from the `x` argument.
	template<typename T>
	constexpr T RoundDown(T x, typename Identity<T>::type n) WARN_UNUSED;

	template<typename T>
	constexpr T RoundDown(T x, typename Identity<T>::type n) {
	DCHECK(IsPowerOfTwo(n));
	return (x & -n);
	}

	template<typename T>
	constexpr T RoundUp(T x, typename std::remove_reference<T>::type n) WARN_UNUSED;

	template<typename T>
	constexpr T RoundUp(T x, typename std::remove_reference<T>::type n) {
	return RoundDown(x + n - 1, n);
	}

	// For aligning pointers.
	template<typename T>
	inline T* AlignDown(T* x, uintptr_t n) WARN_UNUSED;

	template<typename T>
	inline T* AlignDown(T* x, uintptr_t n) {
	return reinterpret_cast<T*>(RoundDown(reinterpret_cast<uintptr_t>(x), n));
	}

	template<typename T>
	inline T* AlignUp(T* x, uintptr_t n) WARN_UNUSED;

	template<typename T>
	inline T* AlignUp(T* x, uintptr_t n) {
	return reinterpret_cast<T*>(RoundUp(reinterpret_cast<uintptr_t>(x), n));
	}

	template<int n, typename T>
	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>
	inline bool IsAligned(T* x) {
	return IsAligned<n>(reinterpret_cast<const uintptr_t>(x));
	}

	template<typename T>
	inline bool IsAlignedParam(T x, int n) {
	return (x & (n - 1)) == 0;
	}

	template<typename T>
	inline bool IsAlignedParam(T* x, int n) {
	return IsAlignedParam(reinterpret_cast<const uintptr_t>(x), n);
	}

	#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)

	inline uint16_t Low16Bits(uint32_t value) {
	return static_cast<uint16_t>(value);
	}

	inline uint16_t High16Bits(uint32_t value) {
	return static_cast<uint16_t>(value >> 16);
	}

	inline uint32_t Low32Bits(uint64_t value) {
	return static_cast<uint32_t>(value);
	}

	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>
	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>
	constexpr T GetIntLimit(size_t bits) {
	DCHECK_NE(bits, 0u);
	DCHECK_LT(bits, BitSizeOf<T>());
	return static_cast<T>(1) << (bits - 1);
	}

	template <size_t kBits, typename T>
	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>
	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.
	using unsigned_type = typename std::make_unsigned<T>::type;
	return (0 <= value) &&
	(kBits == BitSizeOf<T>() \|\|
	(static_cast<unsigned_type>(value) <= GetIntLimit<unsigned_type>(kBits) * 2u - 1u));
	}

	template <size_t kBits, typename T>
	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.");
	using unsigned_type = typename std::make_unsigned<T>::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>
	constexpr T MaxInt(size_t bits) {
	DCHECK(std::is_unsigned<T>::value \|\| bits > 0u) << "bits cannot be zero for signed.";
	DCHECK_LE(bits, BitSizeOf<T>());
	using unsigned_type = typename std::make_unsigned<T>::type;
	return bits == BitSizeOf<T>()
	? std::numeric_limits<T>::max()
	: std::is_signed<T>::value
	? ((bits == 1u) ? 0 : static_cast<T>(MaxInt<unsigned_type>(bits - 1)))
	: static_cast<T>(UINT64_C(1) << bits) - static_cast<T>(1);
	}

	template <typename T>
	constexpr T MinInt(size_t bits) {
	DCHECK(std::is_unsigned<T>::value \|\| bits > 0) << "bits cannot be zero for signed.";
	DCHECK_LE(bits, BitSizeOf<T>());
	return bits == BitSizeOf<T>()
	? std::numeric_limits<T>::min()
	: std::is_signed<T>::value
	? ((bits == 1u) ? -1 : static_cast<T>(-1) - MaxInt<T>(bits))
	: static_cast<T>(0);
	}

	// Returns value with bit set in lowest one-bit position or 0 if 0. (java.lang.X.lowestOneBit).
	template <typename kind>
	inline static kind LowestOneBitValue(kind opnd) {
	// Hacker's Delight, Section 2-1
	return opnd & -opnd;
	}

	// Returns value with bit set in hightest one-bit position or 0 if 0. (java.lang.X.highestOneBit).
	template <typename T>
	inline static T HighestOneBitValue(T opnd) {
	using unsigned_type = typename std::make_unsigned<T>::type;
	T res;
	if (opnd == 0) {
	res = 0;
	} else {
	int bit_position = BitSizeOf<T>() - (CLZ(static_cast<unsigned_type>(opnd)) + 1);
	res = static_cast<T>(UINT64_C(1) << bit_position);
	}
	return res;
	}

	// Rotate bits.
	template <typename T, bool left>
	inline static T Rot(T opnd, int distance) {
	int mask = BitSizeOf<T>() - 1;
	int unsigned_right_shift = left ? (-distance & mask) : (distance & mask);
	int signed_left_shift = left ? (distance & mask) : (-distance & mask);
	using unsigned_type = typename std::make_unsigned<T>::type;
	return (static_cast<unsigned_type>(opnd) >> unsigned_right_shift) \| (opnd << signed_left_shift);
	}

	// TUNING: use rbit for arm/arm64
	inline static uint32_t ReverseBits32(uint32_t opnd) {
	// Hacker's Delight 7-1
	opnd = ((opnd >> 1) & 0x55555555) \| ((opnd & 0x55555555) << 1);
	opnd = ((opnd >> 2) & 0x33333333) \| ((opnd & 0x33333333) << 2);
	opnd = ((opnd >> 4) & 0x0F0F0F0F) \| ((opnd & 0x0F0F0F0F) << 4);
	opnd = ((opnd >> 8) & 0x00FF00FF) \| ((opnd & 0x00FF00FF) << 8);
	opnd = ((opnd >> 16)) \| ((opnd) << 16);
	return opnd;
	}

	// TUNING: use rbit for arm/arm64
	inline static uint64_t ReverseBits64(uint64_t opnd) {
	// Hacker's Delight 7-1
	opnd = (opnd & 0x5555555555555555L) << 1 \| ((opnd >> 1) & 0x5555555555555555L);
	opnd = (opnd & 0x3333333333333333L) << 2 \| ((opnd >> 2) & 0x3333333333333333L);
	opnd = (opnd & 0x0f0f0f0f0f0f0f0fL) << 4 \| ((opnd >> 4) & 0x0f0f0f0f0f0f0f0fL);
	opnd = (opnd & 0x00ff00ff00ff00ffL) << 8 \| ((opnd >> 8) & 0x00ff00ff00ff00ffL);
	opnd = (opnd << 48) \| ((opnd & 0xffff0000L) << 16) \| ((opnd >> 16) & 0xffff0000L) \| (opnd >> 48);
	return opnd;
	}

	// Create a mask for the least significant "bits"
	// The returned value is always unsigned to prevent undefined behavior for bitwise ops.
	//
	// Given 'bits',
	// Returns:
	// <--- bits --->
	// +-----------------+------------+
	// \| 0 ............0 \| 1.....1 \|
	// +-----------------+------------+
	// msb lsb
	template <typename T = size_t>
	inline static constexpr std::make_unsigned_t<T> MaskLeastSignificant(size_t bits) {
	DCHECK_GE(BitSizeOf<T>(), bits) << "Bits out of range for type T";
	using unsigned_T = std::make_unsigned_t<T>;
	if (bits >= BitSizeOf<T>()) {
	return std::numeric_limits<unsigned_T>::max();
	} else {
	auto kOne = static_cast<unsigned_T>(1); // Do not truncate for T>size_t.
	return static_cast<unsigned_T>((kOne << bits) - kOne);
	}
	}

	// Clears the bitfield starting at the least significant bit "lsb" with a bitwidth of 'width'.
	// (Equivalent of ARM BFC instruction).
	//
	// Given:
	// <-- width -->
	// +--------+------------+--------+
	// \| ABC... \| bitfield \| XYZ... +
	// +--------+------------+--------+
	// lsb 0
	// Returns:
	// <-- width -->
	// +--------+------------+--------+
	// \| ABC... \| 0........0 \| XYZ... +
	// +--------+------------+--------+
	// lsb 0
	template <typename T>
	inline static constexpr T BitFieldClear(T value, size_t lsb, size_t width) {
	DCHECK_GE(BitSizeOf(value), lsb + width) << "Bit field out of range for value";
	const auto val = static_cast<std::make_unsigned_t<T>>(value);
	const auto mask = MaskLeastSignificant<T>(width);

	return static_cast<T>(val & ~(mask << lsb));
	}

	// Inserts the contents of 'data' into bitfield of 'value' starting
	// at the least significant bit "lsb" with a bitwidth of 'width'.
	// Note: data must be within range of [MinInt(width), MaxInt(width)].
	// (Equivalent of ARM BFI instruction).
	//
	// Given (data):
	// <-- width -->
	// +--------+------------+--------+
	// \| ABC... \| bitfield \| XYZ... +
	// +--------+------------+--------+
	// lsb 0
	// Returns:
	// <-- width -->
	// +--------+------------+--------+
	// \| ABC... \| 0...data \| XYZ... +
	// +--------+------------+--------+
	// lsb 0

	template <typename T, typename T2>
	inline static constexpr T BitFieldInsert(T value, T2 data, size_t lsb, size_t width) {
	DCHECK_GE(BitSizeOf(value), lsb + width) << "Bit field out of range for value";
	if (width != 0u) {
	DCHECK_GE(MaxInt<T2>(width), data) << "Data out of range [too large] for bitwidth";
	DCHECK_LE(MinInt<T2>(width), data) << "Data out of range [too small] for bitwidth";
	} else {
	DCHECK_EQ(static_cast<T2>(0), data) << "Data out of range [nonzero] for bitwidth 0";
	}
	const auto data_mask = MaskLeastSignificant<T2>(width);
	const auto value_cleared = BitFieldClear(value, lsb, width);

	return static_cast<T>(value_cleared \| ((data & data_mask) << lsb));
	}

	// Extracts the bitfield starting at the least significant bit "lsb" with a bitwidth of 'width'.
	// Signed types are sign-extended during extraction. (Equivalent of ARM UBFX/SBFX instruction).
	//
	// Given:
	// <-- width -->
	// +--------+-------------+-------+
	// \| \| bitfield \| +
	// +--------+-------------+-------+
	// lsb 0
	// (Unsigned) Returns:
	// <-- width -->
	// +----------------+-------------+
	// \| 0... 0 \| bitfield \|
	// +----------------+-------------+
	// 0
	// (Signed) Returns:
	// <-- width -->
	// +----------------+-------------+
	// \| S... S \| bitfield \|
	// +----------------+-------------+
	// 0
	// where S is the highest bit in 'bitfield'.
	template <typename T>
	inline static constexpr T BitFieldExtract(T value, size_t lsb, size_t width) {
	DCHECK_GE(BitSizeOf(value), lsb + width) << "Bit field out of range for value";
	const auto val = static_cast<std::make_unsigned_t<T>>(value);

	const T bitfield_unsigned =
	static_cast<T>((val >> lsb) & MaskLeastSignificant<T>(width));
	if (std::is_signed<T>::value) {
	// Perform sign extension
	if (width == 0) { // Avoid underflow.
	return static_cast<T>(0);
	} else if (bitfield_unsigned & (1 << (width - 1))) { // Detect if sign bit was set.
	// MSB <width> LSB
	// 0b11111...100...000000
	const auto ones_negmask = ~MaskLeastSignificant<T>(width);
	return static_cast<T>(bitfield_unsigned \| ones_negmask);
	}
	}
	// Skip sign extension.
	return bitfield_unsigned;
	}

	} // namespace art

	#endif // ART_LIBARTBASE_BASE_BIT_UTILS_H_