include/llvm/MathExtras.h

//===-- llvm/Support/MathExtras.h - Useful math functions -------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains some functions that are useful for math stuff.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_MATHEXTRAS_H
#define LLVM_SUPPORT_MATHEXTRAS_H

#include "llvm/Compiler.h"
#include <cstdint>
#include <limits>

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

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 || _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 _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 _MSC_VER
    unsigned long Index;
    _BitScanReverse64(&Index, Val);
    return Index ^ 63;
#endif
  }
};
#endif
#endif
} // namespace detail

/// \brief 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 detail::LeadingZerosCounter<T, sizeof(T)>::count(Val, ZB);
}

/// Log2_32 - This function returns 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);
}

/// Log2_64 - This function returns 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);
}

/// Log2_32_Ceil - This function returns 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);
}

/// Log2_64_Ceil - This function returns 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);
}

/// BitsToDouble - This function takes a 64-bit integer and returns the bit
/// equivalent double.
inline double BitsToDouble(uint64_t Bits) {
  union {
    uint64_t L;
    double D;
  } T;
  T.L = Bits;
  return T.D;
}

/// BitsToFloat - This function takes a 32-bit integer and returns the bit
/// equivalent float.
inline float BitsToFloat(uint32_t Bits) {
  union {
    uint32_t I;
    float F;
  } T;
  T.I = Bits;
  return T.F;
}

/// DoubleToBits - 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) {
  union {
    uint64_t L;
    double D;
  } T;
  T.D = Double;
  return T.L;
}

/// FloatToBits - 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) {
  union {
    uint32_t I;
    float F;
  } T;
  T.F = Float;
  return T.I;
}

/// NextPowerOf2 - 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;
}

} // namespace llvm

#endif