c10/util/llvmMathExtras.h

//===-- llvm/Support/MathExtras.h - Useful math functions -------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains some functions that are useful for math stuff.
 //
 //===----------------------------------------------------------------------===//

 #ifndef LLVM_SUPPORT_MATHEXTRAS_H
 #define LLVM_SUPPORT_MATHEXTRAS_H

 #include <algorithm>
 #include <cmath>
 #include <cassert>
 #include <climits>
 #include <cstring>
 #include <limits>
 #include <type_traits>

 #ifdef __ANDROID_NDK__
 #include <android/api-level.h>
 #endif

 #ifndef __has_builtin
 # define __has_builtin(x) 0
 #endif

 #ifndef LLVM_GNUC_PREREQ
 # if defined(__GNUC__) && defined(__GNUC_MINOR__) && defined(__GNUC_PATCHLEVEL__)
 #  define LLVM_GNUC_PREREQ(maj, min, patch) \
     ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) + __GNUC_PATCHLEVEL__ >= \
      ((maj) << 20) + ((min) << 10) + (patch))
 # elif defined(__GNUC__) && defined(__GNUC_MINOR__)
 #  define LLVM_GNUC_PREREQ(maj, min, patch) \
     ((__GNUC__ << 20) + (__GNUC_MINOR__ << 10) >= ((maj) << 20) + ((min) << 10))
 # else
 #  define LLVM_GNUC_PREREQ(maj, min, patch) 0
 # endif
 #endif

 #ifdef _MSC_VER
 // Declare these intrinsics manually rather including intrin.h. It's very
 // expensive, and MathExtras.h is popular.
 // #include <intrin.h>
 extern "C" {
 unsigned char _BitScanForward(unsigned long *_Index, unsigned long _Mask);
 unsigned char _BitScanForward64(unsigned long *_Index, unsigned __int64 _Mask);
 unsigned char _BitScanReverse(unsigned long *_Index, unsigned long _Mask);
 unsigned char _BitScanReverse64(unsigned long *_Index, unsigned __int64 _Mask);
 }
 #endif

 namespace llvm {
 /// The behavior an operation has on an input of 0.
 enum ZeroBehavior {
   /// The returned value is undefined.
   ZB_Undefined,
   /// The returned value is numeric_limits<T>::max()
   ZB_Max,
   /// The returned value is numeric_limits<T>::digits
   ZB_Width
 };

 namespace detail {
 template <typename T, std::size_t SizeOfT> struct TrailingZerosCounter {
   static std::size_t count(T Val, ZeroBehavior) {
     if (!Val)
       return std::numeric_limits<T>::digits;
     if (Val & 0x1)
       return 0;

     // Bisection method.
     std::size_t ZeroBits = 0;
     T Shift = std::numeric_limits<T>::digits >> 1;
     T Mask = std::numeric_limits<T>::max() >> Shift;
     while (Shift) {
       if ((Val & Mask) == 0) {
         Val >>= Shift;
         ZeroBits |= Shift;
       }
       Shift >>= 1;
       Mask >>= Shift;
     }
     return ZeroBits;
   }
 };

 #if __GNUC__ >= 4 || defined(_MSC_VER)
 template <typename T> struct TrailingZerosCounter<T, 4> {
   static std::size_t count(T Val, ZeroBehavior ZB) {
     if (ZB != ZB_Undefined && Val == 0)
       return 32;

 #if __has_builtin(__builtin_ctz) || LLVM_GNUC_PREREQ(4, 0, 0)
     return __builtin_ctz(Val);
 #elif defined(_MSC_VER)
     unsigned long Index;
     _BitScanForward(&Index, Val);
     return Index;
 #endif
   }
 };

 #if !defined(_MSC_VER) || defined(_M_X64)
 template <typename T> struct TrailingZerosCounter<T, 8> {
   static std::size_t count(T Val, ZeroBehavior ZB) {
     if (ZB != ZB_Undefined && Val == 0)
       return 64;

 #if __has_builtin(__builtin_ctzll) || LLVM_GNUC_PREREQ(4, 0, 0)
     return __builtin_ctzll(Val);
 #elif defined(_MSC_VER)
     unsigned long Index;
     _BitScanForward64(&Index, Val);
     return Index;
 #endif
   }
 };
 #endif
 #endif
 } // namespace detail

 /// Count number of 0's from the least significant bit to the most
 ///   stopping at the first 1.
 ///
 /// Only unsigned integral types are allowed.
 ///
 /// \param ZB the behavior on an input of 0. Only ZB_Width and ZB_Undefined are
 ///   valid arguments.
 template <typename T>
 std::size_t countTrailingZeros(T Val, ZeroBehavior ZB = ZB_Width) {
   static_assert(std::numeric_limits<T>::is_integer &&
                     !std::numeric_limits<T>::is_signed,
                 "Only unsigned integral types are allowed.");
   return llvm::detail::TrailingZerosCounter<T, sizeof(T)>::count(Val, ZB);
 }

 namespace detail {
 template <typename T, std::size_t SizeOfT> struct LeadingZerosCounter {
   static std::size_t count(T Val, ZeroBehavior) {
     if (!Val)
       return std::numeric_limits<T>::digits;

     // Bisection method.
     std::size_t ZeroBits = 0;
     for (T Shift = std::numeric_limits<T>::digits >> 1; Shift; Shift >>= 1) {
       T Tmp = Val >> Shift;
       if (Tmp)
         Val = Tmp;
       else
         ZeroBits |= Shift;
     }
     return ZeroBits;
   }
 };

 #if __GNUC__ >= 4 || defined(_MSC_VER)
 template <typename T> struct LeadingZerosCounter<T, 4> {
   static std::size_t count(T Val, ZeroBehavior ZB) {
     if (ZB != ZB_Undefined && Val == 0)
       return 32;

 #if __has_builtin(__builtin_clz) || LLVM_GNUC_PREREQ(4, 0, 0)
     return __builtin_clz(Val);
 #elif defined(_MSC_VER)
     unsigned long Index;
     _BitScanReverse(&Index, Val);
     return Index ^ 31;
 #endif
   }
 };

 #if !defined(_MSC_VER) || defined(_M_X64)
 template <typename T> struct LeadingZerosCounter<T, 8> {
   static std::size_t count(T Val, ZeroBehavior ZB) {
     if (ZB != ZB_Undefined && Val == 0)
       return 64;

 #if __has_builtin(__builtin_clzll) || LLVM_GNUC_PREREQ(4, 0, 0)
     return __builtin_clzll(Val);
 #elif defined(_MSC_VER)
     unsigned long Index;
     _BitScanReverse64(&Index, Val);
     return Index ^ 63;
 #endif
   }
 };
 #endif
 #endif
 } // namespace detail

 /// Count number of 0's from the most significant bit to the least
 ///   stopping at the first 1.
 ///
 /// Only unsigned integral types are allowed.
 ///
 /// \param ZB the behavior on an input of 0. Only ZB_Width and ZB_Undefined are
 ///   valid arguments.
 template <typename T>
 std::size_t countLeadingZeros(T Val, ZeroBehavior ZB = ZB_Width) {
   static_assert(std::numeric_limits<T>::is_integer &&
                     !std::numeric_limits<T>::is_signed,
                 "Only unsigned integral types are allowed.");
   return llvm::detail::LeadingZerosCounter<T, sizeof(T)>::count(Val, ZB);
 }

 /// Get the index of the first set bit starting from the least
 ///   significant bit.
 ///
 /// Only unsigned integral types are allowed.
 ///
 /// \param ZB the behavior on an input of 0. Only ZB_Max and ZB_Undefined are
 ///   valid arguments.
 template <typename T> T findFirstSet(T Val, ZeroBehavior ZB = ZB_Max) {
   if (ZB == ZB_Max && Val == 0)
     return std::numeric_limits<T>::max();

   return countTrailingZeros(Val, ZB_Undefined);
 }

 /// Create a bitmask with the N right-most bits set to 1, and all other
 /// bits set to 0.  Only unsigned types are allowed.
 template <typename T> T maskTrailingOnes(unsigned N) {
   static_assert(std::is_unsigned<T>::value, "Invalid type!");
   const unsigned Bits = CHAR_BIT * sizeof(T);
   assert(N <= Bits && "Invalid bit index");
   return N == 0 ? 0 : (T(-1) >> (Bits - N));
 }

 /// Create a bitmask with the N left-most bits set to 1, and all other
 /// bits set to 0.  Only unsigned types are allowed.
 template <typename T> T maskLeadingOnes(unsigned N) {
   return ~maskTrailingOnes<T>(CHAR_BIT * sizeof(T) - N);
 }

 /// Create a bitmask with the N right-most bits set to 0, and all other
 /// bits set to 1.  Only unsigned types are allowed.
 template <typename T> T maskTrailingZeros(unsigned N) {
   return maskLeadingOnes<T>(CHAR_BIT * sizeof(T) - N);
 }

 /// Create a bitmask with the N left-most bits set to 0, and all other
 /// bits set to 1.  Only unsigned types are allowed.
 template <typename T> T maskLeadingZeros(unsigned N) {
   return maskTrailingOnes<T>(CHAR_BIT * sizeof(T) - N);
 }

 /// Get the index of the last set bit starting from the least
 ///   significant bit.
 ///
 /// Only unsigned integral types are allowed.
 ///
 /// \param ZB the behavior on an input of 0. Only ZB_Max and ZB_Undefined are
 ///   valid arguments.
 template <typename T> T findLastSet(T Val, ZeroBehavior ZB = ZB_Max) {
   if (ZB == ZB_Max && Val == 0)
     return std::numeric_limits<T>::max();

   // Use ^ instead of - because both gcc and llvm can remove the associated ^
   // in the __builtin_clz intrinsic on x86.
   return countLeadingZeros(Val, ZB_Undefined) ^
          (std::numeric_limits<T>::digits - 1);
 }

 /// Macro compressed bit reversal table for 256 bits.
 ///
 /// http://graphics.stanford.edu/~seander/bithacks.html#BitReverseTable
 static const unsigned char BitReverseTable256[256] = {
 #define R2(n) n, n + 2 * 64, n + 1 * 64, n + 3 * 64
 #define R4(n) R2(n), R2(n + 2 * 16), R2(n + 1 * 16), R2(n + 3 * 16)
 #define R6(n) R4(n), R4(n + 2 * 4), R4(n + 1 * 4), R4(n + 3 * 4)
   R6(0), R6(2), R6(1), R6(3)
 #undef R2
 #undef R4
 #undef R6
 };

 /// Reverse the bits in \p Val.
 template <typename T>
 T reverseBits(T Val) {
   unsigned char in[sizeof(Val)];
   unsigned char out[sizeof(Val)];
   std::memcpy(in, &Val, sizeof(Val));
   for (unsigned i = 0; i < sizeof(Val); ++i)
     out[(sizeof(Val) - i) - 1] = BitReverseTable256[in[i]];
   std::memcpy(&Val, out, sizeof(Val));
   return Val;
 }

 // NOTE: The following support functions use the _32/_64 extensions instead of
 // type overloading so that signed and unsigned integers can be used without
 // ambiguity.

 /// Return the high 32 bits of a 64 bit value.
 constexpr inline uint32_t Hi_32(uint64_t Value) {
   return static_cast<uint32_t>(Value >> 32);
 }

 /// Return the low 32 bits of a 64 bit value.
 constexpr inline uint32_t Lo_32(uint64_t Value) {
   return static_cast<uint32_t>(Value);
 }

 /// Make a 64-bit integer from a high / low pair of 32-bit integers.
 constexpr inline uint64_t Make_64(uint32_t High, uint32_t Low) {
   return ((uint64_t)High << 32) | (uint64_t)Low;
 }

 /// Checks if an integer fits into the given bit width.
 template <unsigned N> constexpr inline bool isInt(int64_t x) {
   return N >= 64 || (-(INT64_C(1)<<(N-1)) <= x && x < (INT64_C(1)<<(N-1)));
 }
 // Template specializations to get better code for common cases.
 template <> constexpr inline bool isInt<8>(int64_t x) {
   return static_cast<int8_t>(x) == x;
 }
 template <> constexpr inline bool isInt<16>(int64_t x) {
   return static_cast<int16_t>(x) == x;
 }
 template <> constexpr inline bool isInt<32>(int64_t x) {
   return static_cast<int32_t>(x) == x;
 }

 /// Checks if a signed integer is an N bit number shifted left by S.
 template <unsigned N, unsigned S>
 constexpr inline bool isShiftedInt(int64_t x) {
   static_assert(
       N > 0, "isShiftedInt<0> doesn't make sense (refers to a 0-bit number.");
   static_assert(N + S <= 64, "isShiftedInt<N, S> with N + S > 64 is too wide.");
   return isInt<N + S>(x) && (x % (UINT64_C(1) << S) == 0);
 }

 /// Checks if an unsigned integer fits into the given bit width.
 ///
 /// This is written as two functions rather than as simply
 ///
 ///   return N >= 64 || X < (UINT64_C(1) << N);
 ///
 /// to keep MSVC from (incorrectly) warning on isUInt<64> that we're shifting
 /// left too many places.
 template <unsigned N>
 constexpr inline typename std::enable_if<(N < 64), bool>::type
 isUInt(uint64_t X) {
   static_assert(N > 0, "isUInt<0> doesn't make sense");
   return X < (UINT64_C(1) << (N));
 }
 template <unsigned N>
 constexpr inline typename std::enable_if<N >= 64, bool>::type
 isUInt(uint64_t X) {
   return true;
 }

 // Template specializations to get better code for common cases.
 template <> constexpr inline bool isUInt<8>(uint64_t x) {
   return static_cast<uint8_t>(x) == x;
 }
 template <> constexpr inline bool isUInt<16>(uint64_t x) {
   return static_cast<uint16_t>(x) == x;
 }
 template <> constexpr inline bool isUInt<32>(uint64_t x) {
   return static_cast<uint32_t>(x) == x;
 }

 /// Checks if a unsigned integer is an N bit number shifted left by S.
 template <unsigned N, unsigned S>
 constexpr inline bool isShiftedUInt(uint64_t x) {
   static_assert(
       N > 0, "isShiftedUInt<0> doesn't make sense (refers to a 0-bit number)");
   static_assert(N + S <= 64,
                 "isShiftedUInt<N, S> with N + S > 64 is too wide.");
   // Per the two static_asserts above, S must be strictly less than 64.  So
   // 1 << S is not undefined behavior.
   return isUInt<N + S>(x) && (x % (UINT64_C(1) << S) == 0);
 }

 /// Gets the maximum value for a N-bit unsigned integer.
 inline uint64_t maxUIntN(uint64_t N) {
   assert(N > 0 && N <= 64 && "integer width out of range");

   // uint64_t(1) << 64 is undefined behavior, so we can't do
   //   (uint64_t(1) << N) - 1
   // without checking first that N != 64.  But this works and doesn't have a
   // branch.
   return UINT64_MAX >> (64 - N);
 }

 /// Gets the minimum value for a N-bit signed integer.
 inline int64_t minIntN(int64_t N) {
   assert(N > 0 && N <= 64 && "integer width out of range");

   return -(UINT64_C(1)<<(N-1));
 }

 /// Gets the maximum value for a N-bit signed integer.
 inline int64_t maxIntN(int64_t N) {
   assert(N > 0 && N <= 64 && "integer width out of range");

   // This relies on two's complement wraparound when N == 64, so we convert to
   // int64_t only at the very end to avoid UB.
   return (UINT64_C(1) << (N - 1)) - 1;
 }

 /// Checks if an unsigned integer fits into the given (dynamic) bit width.
 inline bool isUIntN(unsigned N, uint64_t x) {
   return N >= 64 || x <= maxUIntN(N);
 }

 /// Checks if an signed integer fits into the given (dynamic) bit width.
 inline bool isIntN(unsigned N, int64_t x) {
   return N >= 64 || (minIntN(N) <= x && x <= maxIntN(N));
 }

 /// Return true if the argument is a non-empty sequence of ones starting at the
 /// least significant bit with the remainder zero (32 bit version).
 /// Ex. isMask_32(0x0000FFFFU) == true.
 constexpr inline bool isMask_32(uint32_t Value) {
   return Value && ((Value + 1) & Value) == 0;
 }

 /// Return true if the argument is a non-empty sequence of ones starting at the
 /// least significant bit with the remainder zero (64 bit version).
 constexpr inline bool isMask_64(uint64_t Value) {
   return Value && ((Value + 1) & Value) == 0;
 }

 /// Return true if the argument contains a non-empty sequence of ones with the
 /// remainder zero (32 bit version.) Ex. isShiftedMask_32(0x0000FF00U) == true.
 constexpr inline bool isShiftedMask_32(uint32_t Value) {
   return Value && isMask_32((Value - 1) | Value);
 }

 /// Return true if the argument contains a non-empty sequence of ones with the
 /// remainder zero (64 bit version.)
 constexpr inline bool isShiftedMask_64(uint64_t Value) {
   return Value && isMask_64((Value - 1) | Value);
 }

 /// Return true if the argument is a power of two > 0.
 /// Ex. isPowerOf2_32(0x00100000U) == true (32 bit edition.)
 constexpr inline bool isPowerOf2_32(uint32_t Value) {
   return Value && !(Value & (Value - 1));
 }

 /// Return true if the argument is a power of two > 0 (64 bit edition.)
 constexpr inline bool isPowerOf2_64(uint64_t Value) {
   return Value && !(Value & (Value - 1));
 }

 /// Count the number of ones from the most significant bit to the first
 /// zero bit.
 ///
 /// Ex. countLeadingOnes(0xFF0FFF00) == 8.
 /// Only unsigned integral types are allowed.
 ///
 /// \param ZB the behavior on an input of all ones. Only ZB_Width and
 /// ZB_Undefined are valid arguments.
 template <typename T>
 std::size_t countLeadingOnes(T Value, ZeroBehavior ZB = ZB_Width) {
   static_assert(std::numeric_limits<T>::is_integer &&
                     !std::numeric_limits<T>::is_signed,
                 "Only unsigned integral types are allowed.");
   return countLeadingZeros<T>(~Value, ZB);
 }

 /// Count the number of ones from the least significant bit to the first
 /// zero bit.
 ///
 /// Ex. countTrailingOnes(0x00FF00FF) == 8.
 /// Only unsigned integral types are allowed.
 ///
 /// \param ZB the behavior on an input of all ones. Only ZB_Width and
 /// ZB_Undefined are valid arguments.
 template <typename T>
 std::size_t countTrailingOnes(T Value, ZeroBehavior ZB = ZB_Width) {
   static_assert(std::numeric_limits<T>::is_integer &&
                     !std::numeric_limits<T>::is_signed,
                 "Only unsigned integral types are allowed.");
   return countTrailingZeros<T>(~Value, ZB);
 }

 namespace detail {
 template <typename T, std::size_t SizeOfT> struct PopulationCounter {
   static unsigned count(T Value) {
     // Generic version, forward to 32 bits.
     static_assert(SizeOfT <= 4, "Not implemented!");
 #if __GNUC__ >= 4
     return __builtin_popcount(Value);
 #else
     uint32_t v = Value;
     v = v - ((v >> 1) & 0x55555555);
     v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
     return ((v + (v >> 4) & 0xF0F0F0F) * 0x1010101) >> 24;
 #endif
   }
 };

 template <typename T> struct PopulationCounter<T, 8> {
   static unsigned count(T Value) {
 #if __GNUC__ >= 4
     return __builtin_popcountll(Value);
 #else
     uint64_t v = Value;
     v = v - ((v >> 1) & 0x5555555555555555ULL);
     v = (v & 0x3333333333333333ULL) + ((v >> 2) & 0x3333333333333333ULL);
     v = (v + (v >> 4)) & 0x0F0F0F0F0F0F0F0FULL;
     return unsigned((uint64_t)(v * 0x0101010101010101ULL) >> 56);
 #endif
   }
 };
 } // namespace detail

 /// Count the number of set bits in a value.
 /// Ex. countPopulation(0xF000F000) = 8
 /// Returns 0 if the word is zero.
 template <typename T>
 inline unsigned countPopulation(T Value) {
   static_assert(std::numeric_limits<T>::is_integer &&
                     !std::numeric_limits<T>::is_signed,
                 "Only unsigned integral types are allowed.");
   return detail::PopulationCounter<T, sizeof(T)>::count(Value);
 }

 /// Return the log base 2 of the specified value.
 inline double Log2(double Value) {
 #if defined(__ANDROID_API__) && __ANDROID_API__ < 18
   return __builtin_log(Value) / __builtin_log(2.0);
 #else
   return log2(Value);
 #endif
 }

 /// Return the floor log base 2 of the specified value, -1 if the value is zero.
 /// (32 bit edition.)
 /// Ex. Log2_32(32) == 5, Log2_32(1) == 0, Log2_32(0) == -1, Log2_32(6) == 2
 inline unsigned Log2_32(uint32_t Value) {
   return 31 - countLeadingZeros(Value);
 }

 /// Return the floor log base 2 of the specified value, -1 if the value is zero.
 /// (64 bit edition.)
 inline unsigned Log2_64(uint64_t Value) {
   return 63 - countLeadingZeros(Value);
 }

 /// Return the ceil log base 2 of the specified value, 32 if the value is zero.
 /// (32 bit edition).
 /// Ex. Log2_32_Ceil(32) == 5, Log2_32_Ceil(1) == 0, Log2_32_Ceil(6) == 3
 inline unsigned Log2_32_Ceil(uint32_t Value) {
   return 32 - countLeadingZeros(Value - 1);
 }

 /// Return the ceil log base 2 of the specified value, 64 if the value is zero.
 /// (64 bit edition.)
 inline unsigned Log2_64_Ceil(uint64_t Value) {
   return 64 - countLeadingZeros(Value - 1);
 }

 /// Return the greatest common divisor of the values using Euclid's algorithm.
 inline uint64_t GreatestCommonDivisor64(uint64_t A, uint64_t B) {
   while (B) {
     uint64_t T = B;
     B = A % B;
     A = T;
   }
   return A;
 }

 /// This function takes a 64-bit integer and returns the bit equivalent double.
 inline double BitsToDouble(uint64_t Bits) {
   double D;
   static_assert(sizeof(uint64_t) == sizeof(double), "Unexpected type sizes");
   memcpy(&D, &Bits, sizeof(Bits));
   return D;
 }

 /// This function takes a 32-bit integer and returns the bit equivalent float.
 inline float BitsToFloat(uint32_t Bits) {
   float F;
   static_assert(sizeof(uint32_t) == sizeof(float), "Unexpected type sizes");
   memcpy(&F, &Bits, sizeof(Bits));
   return F;
 }

 /// This function takes a double and returns the bit equivalent 64-bit integer.
 /// Note that copying doubles around changes the bits of NaNs on some hosts,
 /// notably x86, so this routine cannot be used if these bits are needed.
 inline uint64_t DoubleToBits(double Double) {
   uint64_t Bits;
   static_assert(sizeof(uint64_t) == sizeof(double), "Unexpected type sizes");
   memcpy(&Bits, &Double, sizeof(Double));
   return Bits;
 }

 /// This function takes a float and returns the bit equivalent 32-bit integer.
 /// Note that copying floats around changes the bits of NaNs on some hosts,
 /// notably x86, so this routine cannot be used if these bits are needed.
 inline uint32_t FloatToBits(float Float) {
   uint32_t Bits;
   static_assert(sizeof(uint32_t) == sizeof(float), "Unexpected type sizes");
   memcpy(&Bits, &Float, sizeof(Float));
   return Bits;
 }

 /// A and B are either alignments or offsets. Return the minimum alignment that
 /// may be assumed after adding the two together.
 constexpr inline uint64_t MinAlign(uint64_t A, uint64_t B) {
   // The largest power of 2 that divides both A and B.
   //
   // Replace "-Value" by "1+~Value" in the following commented code to avoid
   // MSVC warning C4146
   //    return (A | B) & -(A | B);
   return (A | B) & (1 + ~(A | B));
 }

 /// Aligns \c Addr to \c Alignment bytes, rounding up.
 ///
 /// Alignment should be a power of two.  This method rounds up, so
 /// alignAddr(7, 4) == 8 and alignAddr(8, 4) == 8.
 inline uintptr_t alignAddr(const void *Addr, size_t Alignment) {
   assert(Alignment && isPowerOf2_64((uint64_t)Alignment) &&
          "Alignment is not a power of two!");

   assert((uintptr_t)Addr + Alignment - 1 >= (uintptr_t)Addr);

   return (((uintptr_t)Addr + Alignment - 1) & ~(uintptr_t)(Alignment - 1));
 }

 /// Returns the necessary adjustment for aligning \c Ptr to \c Alignment
 /// bytes, rounding up.
 inline size_t alignmentAdjustment(const void *Ptr, size_t Alignment) {
   return alignAddr(Ptr, Alignment) - (uintptr_t)Ptr;
 }

 /// Returns the next power of two (in 64-bits) that is strictly greater than A.
 /// Returns zero on overflow.
 inline uint64_t NextPowerOf2(uint64_t A) {
   A |= (A >> 1);
   A |= (A >> 2);
   A |= (A >> 4);
   A |= (A >> 8);
   A |= (A >> 16);
   A |= (A >> 32);
   return A + 1;
 }

 /// Returns the power of two which is less than or equal to the given value.
 /// Essentially, it is a floor operation across the domain of powers of two.
 inline uint64_t PowerOf2Floor(uint64_t A) {
   if (!A) return 0;
   return 1ull << (63 - countLeadingZeros(A, ZB_Undefined));
 }

 /// Returns the power of two which is greater than or equal to the given value.
 /// Essentially, it is a ceil operation across the domain of powers of two.
 inline uint64_t PowerOf2Ceil(uint64_t A) {
   if (!A)
     return 0;
   return NextPowerOf2(A - 1);
 }

 /// Returns the next integer (mod 2**64) that is greater than or equal to
 /// \p Value and is a multiple of \p Align. \p Align must be non-zero.
 ///
 /// If non-zero \p Skew is specified, the return value will be a minimal
 /// integer that is greater than or equal to \p Value and equal to
 /// \p Align * N + \p Skew for some integer N. If \p Skew is larger than
 /// \p Align, its value is adjusted to '\p Skew mod \p Align'.
 ///
 /// Examples:
 /// \code
 ///   alignTo(5, 8) = 8
 ///   alignTo(17, 8) = 24
 ///   alignTo(~0LL, 8) = 0
 ///   alignTo(321, 255) = 510
 ///
 ///   alignTo(5, 8, 7) = 7
 ///   alignTo(17, 8, 1) = 17
 ///   alignTo(~0LL, 8, 3) = 3
 ///   alignTo(321, 255, 42) = 552
 /// \endcode
 inline uint64_t alignTo(uint64_t Value, uint64_t Align, uint64_t Skew = 0) {
   assert(Align != 0u && "Align can't be 0.");
   Skew %= Align;
   return (Value + Align - 1 - Skew) / Align * Align + Skew;
 }

 /// Returns the next integer (mod 2**64) that is greater than or equal to
 /// \p Value and is a multiple of \c Align. \c Align must be non-zero.
 template <uint64_t Align> constexpr inline uint64_t alignTo(uint64_t Value) {
   static_assert(Align != 0u, "Align must be non-zero");
   return (Value + Align - 1) / Align * Align;
 }

 /// Returns the integer ceil(Numerator / Denominator).
 inline uint64_t divideCeil(uint64_t Numerator, uint64_t Denominator) {
   return alignTo(Numerator, Denominator) / Denominator;
 }

 /// \c alignTo for contexts where a constant expression is required.
 /// \sa alignTo
 ///
 /// \todo FIXME: remove when \c constexpr becomes really \c constexpr
 template <uint64_t Align>
 struct AlignTo {
   static_assert(Align != 0u, "Align must be non-zero");
   template <uint64_t Value>
   struct from_value {
     static const uint64_t value = (Value + Align - 1) / Align * Align;
   };
 };

 /// Returns the largest uint64_t less than or equal to \p Value and is
 /// \p Skew mod \p Align. \p Align must be non-zero
 inline uint64_t alignDown(uint64_t Value, uint64_t Align, uint64_t Skew = 0) {
   assert(Align != 0u && "Align can't be 0.");
   Skew %= Align;
   return (Value - Skew) / Align * Align + Skew;
 }

 /// Returns the offset to the next integer (mod 2**64) that is greater than
 /// or equal to \p Value and is a multiple of \p Align. \p Align must be
 /// non-zero.
 inline uint64_t OffsetToAlignment(uint64_t Value, uint64_t Align) {
   return alignTo(Value, Align) - Value;
 }

 /// Sign-extend the number in the bottom B bits of X to a 32-bit integer.
 /// Requires 0 < B <= 32.
 template <unsigned B> constexpr inline int32_t SignExtend32(uint32_t X) {
   static_assert(B > 0, "Bit width can't be 0.");
   static_assert(B <= 32, "Bit width out of range.");
   return int32_t(X << (32 - B)) >> (32 - B);
 }

 /// Sign-extend the number in the bottom B bits of X to a 32-bit integer.
 /// Requires 0 < B < 32.
 inline int32_t SignExtend32(uint32_t X, unsigned B) {
   assert(B > 0 && "Bit width can't be 0.");
   assert(B <= 32 && "Bit width out of range.");
   return int32_t(X << (32 - B)) >> (32 - B);
 }

 /// Sign-extend the number in the bottom B bits of X to a 64-bit integer.
 /// Requires 0 < B < 64.
 template <unsigned B> constexpr inline int64_t SignExtend64(uint64_t x) {
   static_assert(B > 0, "Bit width can't be 0.");
   static_assert(B <= 64, "Bit width out of range.");
   return int64_t(x << (64 - B)) >> (64 - B);
 }

 /// Sign-extend the number in the bottom B bits of X to a 64-bit integer.
 /// Requires 0 < B < 64.
 inline int64_t SignExtend64(uint64_t X, unsigned B) {
   assert(B > 0 && "Bit width can't be 0.");
   assert(B <= 64 && "Bit width out of range.");
   return int64_t(X << (64 - B)) >> (64 - B);
 }

 /// Subtract two unsigned integers, X and Y, of type T and return the absolute
 /// value of the result.
 template <typename T>
 typename std::enable_if<std::is_unsigned<T>::value, T>::type
 AbsoluteDifference(T X, T Y) {
   return std::max(X, Y) - std::min(X, Y);
 }

 /// Add two unsigned integers, X and Y, of type T.  Clamp the result to the
 /// maximum representable value of T on overflow.  ResultOverflowed indicates if
 /// the result is larger than the maximum representable value of type T.
 template <typename T>
 typename std::enable_if<std::is_unsigned<T>::value, T>::type
 SaturatingAdd(T X, T Y, bool *ResultOverflowed = nullptr) {
   bool Dummy;
   bool &Overflowed = ResultOverflowed ? *ResultOverflowed : Dummy;
   // Hacker's Delight, p. 29
   T Z = X + Y;
   Overflowed = (Z < X || Z < Y);
   if (Overflowed)
     return std::numeric_limits<T>::max();
   else
     return Z;
 }

 /// Multiply two unsigned integers, X and Y, of type T.  Clamp the result to the
 /// maximum representable value of T on overflow.  ResultOverflowed indicates if
 /// the result is larger than the maximum representable value of type T.
 template <typename T>
 typename std::enable_if<std::is_unsigned<T>::value, T>::type
 SaturatingMultiply(T X, T Y, bool *ResultOverflowed = nullptr) {
   bool Dummy;
   bool &Overflowed = ResultOverflowed ? *ResultOverflowed : Dummy;

   // Hacker's Delight, p. 30 has a different algorithm, but we don't use that
   // because it fails for uint16_t (where multiplication can have undefined
   // behavior due to promotion to int), and requires a division in addition
   // to the multiplication.

   Overflowed = false;

   // Log2(Z) would be either Log2Z or Log2Z + 1.
   // Special case: if X or Y is 0, Log2_64 gives -1, and Log2Z
   // will necessarily be less than Log2Max as desired.
   int Log2Z = Log2_64(X) + Log2_64(Y);
   const T Max = std::numeric_limits<T>::max();
   int Log2Max = Log2_64(Max);
   if (Log2Z < Log2Max) {
     return X * Y;
   }
   if (Log2Z > Log2Max) {
     Overflowed = true;
     return Max;
   }

   // We're going to use the top bit, and maybe overflow one
   // bit past it. Multiply all but the bottom bit then add
   // that on at the end.
   T Z = (X >> 1) * Y;
   if (Z & ~(Max >> 1)) {
     Overflowed = true;
     return Max;
   }
   Z <<= 1;
   if (X & 1)
     return SaturatingAdd(Z, Y, ResultOverflowed);

   return Z;
 }

 /// Multiply two unsigned integers, X and Y, and add the unsigned integer, A to
 /// the product. Clamp the result to the maximum representable value of T on
 /// overflow. ResultOverflowed indicates if the result is larger than the
 /// maximum representable value of type T.
 template <typename T>
 typename std::enable_if<std::is_unsigned<T>::value, T>::type
 SaturatingMultiplyAdd(T X, T Y, T A, bool *ResultOverflowed = nullptr) {
   bool Dummy;
   bool &Overflowed = ResultOverflowed ? *ResultOverflowed : Dummy;

   T Product = SaturatingMultiply(X, Y, &Overflowed);
   if (Overflowed)
     return Product;

   return SaturatingAdd(A, Product, &Overflowed);
 }

 /// Use this rather than HUGE_VALF; the latter causes warnings on MSVC.
 extern const float huge_valf;
 } // End llvm namespace

 #endif