src/utils.h

// Copyright 2012 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_UTILS_H_
#define V8_UTILS_H_

#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <cmath>
#include <string>
#include <type_traits>

#include "include/v8.h"
#include "src/allocation.h"
#include "src/base/bits.h"
#include "src/base/compiler-specific.h"
#include "src/base/logging.h"
#include "src/base/macros.h"
#include "src/base/platform/platform.h"
#include "src/base/v8-fallthrough.h"
#include "src/globals.h"
#include "src/third_party/siphash/halfsiphash.h"
#include "src/vector.h"

#if defined(V8_OS_AIX)
#include <fenv.h>  // NOLINT(build/c++11)
#endif

namespace v8 {
namespace internal {

// ----------------------------------------------------------------------------
// General helper functions

// Returns the value (0 .. 15) of a hexadecimal character c.
// If c is not a legal hexadecimal character, returns a value < 0.
inline int HexValue(uc32 c) {
  c -= '0';
  if (static_cast<unsigned>(c) <= 9) return c;
  c = (c | 0x20) - ('a' - '0');  // detect 0x11..0x16 and 0x31..0x36.
  if (static_cast<unsigned>(c) <= 5) return c + 10;
  return -1;
}

inline char HexCharOfValue(int value) {
  DCHECK(0 <= value && value <= 16);
  if (value < 10) return value + '0';
  return value - 10 + 'A';
}

inline int BoolToInt(bool b) { return b ? 1 : 0; }

// Same as strcmp, but can handle NULL arguments.
inline bool CStringEquals(const char* s1, const char* s2) {
  return (s1 == s2) || (s1 != nullptr && s2 != nullptr && strcmp(s1, s2) == 0);
}

// Checks if value is in range [lower_limit, higher_limit] using a single
// branch.
template <typename T, typename U>
inline constexpr bool IsInRange(T value, U lower_limit, U higher_limit) {
#if V8_CAN_HAVE_DCHECK_IN_CONSTEXPR
  DCHECK(lower_limit <= higher_limit);
#endif
  STATIC_ASSERT(sizeof(U) <= sizeof(T));
  typedef typename std::make_unsigned<T>::type unsigned_T;
  // Use static_cast to support enum classes.
  return static_cast<unsigned_T>(static_cast<unsigned_T>(value) -
                                 static_cast<unsigned_T>(lower_limit)) <=
         static_cast<unsigned_T>(static_cast<unsigned_T>(higher_limit) -
                                 static_cast<unsigned_T>(lower_limit));
}

// Checks if [index, index+length) is in range [0, max). Note that this check
// works even if {index+length} would wrap around.
inline constexpr bool IsInBounds(size_t index, size_t length, size_t max) {
  return length <= max && index <= (max - length);
}

// X must be a power of 2.  Returns the number of trailing zeros.
template <typename T,
          typename = typename std::enable_if<std::is_integral<T>::value>::type>
inline int WhichPowerOf2(T x) {
  DCHECK(base::bits::IsPowerOfTwo(x));
  int bits = 0;
#ifdef DEBUG
  const T original_x = x;
#endif
  constexpr int max_bits = sizeof(T) * 8;
  static_assert(max_bits <= 64, "integral types are not bigger than 64 bits");
// Avoid shifting by more than the bit width of x to avoid compiler warnings.
#define CHECK_BIGGER(s)                                      \
  if (max_bits > s && x >= T{1} << (max_bits > s ? s : 0)) { \
    bits += s;                                               \
    x >>= max_bits > s ? s : 0;                              \
  }
  CHECK_BIGGER(32)
  CHECK_BIGGER(16)
  CHECK_BIGGER(8)
  CHECK_BIGGER(4)
#undef CHECK_BIGGER
  switch (x) {
    default: UNREACHABLE();
    case 8:
      bits++;
      V8_FALLTHROUGH;
    case 4:
      bits++;
      V8_FALLTHROUGH;
    case 2:
      bits++;
      V8_FALLTHROUGH;
    case 1: break;
  }
  DCHECK_EQ(T{1} << bits, original_x);
  return bits;
}

inline int MostSignificantBit(uint32_t x) {
  static const int msb4[] = {0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4};
  int nibble = 0;
  if (x & 0xffff0000) {
    nibble += 16;
    x >>= 16;
  }
  if (x & 0xff00) {
    nibble += 8;
    x >>= 8;
  }
  if (x & 0xf0) {
    nibble += 4;
    x >>= 4;
  }
  return nibble + msb4[x];
}

template <typename T>
static T ArithmeticShiftRight(T x, int shift) {
  DCHECK_LE(0, shift);
  if (x < 0) {
    // Right shift of signed values is implementation defined. Simulate a
    // true arithmetic right shift by adding leading sign bits.
    using UnsignedT = typename std::make_unsigned<T>::type;
    UnsignedT mask = ~(static_cast<UnsignedT>(~0) >> shift);
    return (static_cast<UnsignedT>(x) >> shift) | mask;
  } else {
    return x >> shift;
  }
}

template <typename T>
int Compare(const T& a, const T& b) {
  if (a == b)
    return 0;
  else if (a < b)
    return -1;
  else
    return 1;
}

// Compare function to compare the object pointer value of two
// handlified objects. The handles are passed as pointers to the
// handles.
template<typename T> class Handle;  // Forward declaration.
template <typename T>
int HandleObjectPointerCompare(const Handle<T>* a, const Handle<T>* b) {
  return Compare<T*>(*(*a), *(*b));
}

// Returns the maximum of the two parameters.
template <typename T>
constexpr T Max(T a, T b) {
  return a < b ? b : a;
}


// Returns the minimum of the two parameters.
template <typename T>
constexpr T Min(T a, T b) {
  return a < b ? a : b;
}

// Returns the maximum of the two parameters according to JavaScript semantics.
template <typename T>
T JSMax(T x, T y) {
  if (std::isnan(x)) return x;
  if (std::isnan(y)) return y;
  if (std::signbit(x) < std::signbit(y)) return x;
  return x > y ? x : y;
}

// Returns the maximum of the two parameters according to JavaScript semantics.
template <typename T>
T JSMin(T x, T y) {
  if (std::isnan(x)) return x;
  if (std::isnan(y)) return y;
  if (std::signbit(x) < std::signbit(y)) return y;
  return x > y ? y : x;
}

// Returns the absolute value of its argument.
template <typename T,
          typename = typename std::enable_if<std::is_signed<T>::value>::type>
typename std::make_unsigned<T>::type Abs(T a) {
  // This is a branch-free implementation of the absolute value function and is
  // described in Warren's "Hacker's Delight", chapter 2. It avoids undefined
  // behavior with the arithmetic negation operation on signed values as well.
  typedef typename std::make_unsigned<T>::type unsignedT;
  unsignedT x = static_cast<unsignedT>(a);
  unsignedT y = static_cast<unsignedT>(a >> (sizeof(T) * 8 - 1));
  return (x ^ y) - y;
}

// Returns the negative absolute value of its argument.
template <typename T,
          typename = typename std::enable_if<std::is_signed<T>::value>::type>
T Nabs(T a) {
  return a < 0 ? a : -a;
}

// Floor(-0.0) == 0.0
inline double Floor(double x) {
#if V8_CC_MSVC
  if (x == 0) return x;  // Fix for issue 3477.
#endif
  return std::floor(x);
}

inline double Modulo(double x, double y) {
#if defined(V8_OS_WIN)
  // Workaround MS fmod bugs. ECMA-262 says:
  // dividend is finite and divisor is an infinity => result equals dividend
  // dividend is a zero and divisor is nonzero finite => result equals dividend
  if (!(std::isfinite(x) && (!std::isfinite(y) && !std::isnan(y))) &&
      !(x == 0 && (y != 0 && std::isfinite(y)))) {
    double result = fmod(x, y);
    // Workaround MS bug in VS CRT in some OS versions, https://crbug.com/915045
    // fmod(-17, +/-1) should equal -0.0 but now returns 0.0.
    if (x < 0 && result == 0) result = -0.0;
    x = result;
  }
  return x;
#elif defined(V8_OS_AIX)
  // AIX raises an underflow exception for (Number.MIN_VALUE % Number.MAX_VALUE)
  feclearexcept(FE_ALL_EXCEPT);
  double result = std::fmod(x, y);
  int exception = fetestexcept(FE_UNDERFLOW);
  return (exception ? x : result);
#else
  return std::fmod(x, y);
#endif
}

inline double Pow(double x, double y) {
  if (y == 0.0) return 1.0;
  if (std::isnan(y) || ((x == 1 || x == -1) && std::isinf(y))) {
    return std::numeric_limits<double>::quiet_NaN();
  }
#if (defined(__MINGW64_VERSION_MAJOR) &&                              \
     (!defined(__MINGW64_VERSION_RC) || __MINGW64_VERSION_RC < 1)) || \
    defined(V8_OS_AIX)
  // MinGW64 and AIX have a custom implementation for pow.  This handles certain
  // special cases that are different.
  if ((x == 0.0 || std::isinf(x)) && y != 0.0 && std::isfinite(y)) {
    double f;
    double result = ((x == 0.0) ^ (y > 0)) ? V8_INFINITY : 0;
    /* retain sign if odd integer exponent */
    return ((std::modf(y, &f) == 0.0) && (static_cast<int64_t>(y) & 1))
               ? copysign(result, x)
               : result;
  }

  if (x == 2.0) {
    int y_int = static_cast<int>(y);
    if (y == y_int) {
      return std::ldexp(1.0, y_int);
    }
  }
#endif
  return std::pow(x, y);
}

template <typename T>
T SaturateAdd(T a, T b) {
  if (std::is_signed<T>::value) {
    if (a > 0 && b > 0) {
      if (a > std::numeric_limits<T>::max() - b) {
        return std::numeric_limits<T>::max();
      }
    } else if (a < 0 && b < 0) {
      if (a < std::numeric_limits<T>::min() - b) {
        return std::numeric_limits<T>::min();
      }
    }
  } else {
    CHECK(std::is_unsigned<T>::value);
    if (a > std::numeric_limits<T>::max() - b) {
      return std::numeric_limits<T>::max();
    }
  }
  return a + b;
}

template <typename T>
T SaturateSub(T a, T b) {
  if (std::is_signed<T>::value) {
    if (a >= 0 && b < 0) {
      if (a > std::numeric_limits<T>::max() + b) {
        return std::numeric_limits<T>::max();
      }
    } else if (a < 0 && b > 0) {
      if (a < std::numeric_limits<T>::min() + b) {
        return std::numeric_limits<T>::min();
      }
    }
  } else {
    CHECK(std::is_unsigned<T>::value);
    if (a < b) {
      return static_cast<T>(0);
    }
  }
  return a - b;
}

// ----------------------------------------------------------------------------
// BitField is a help template for encoding and decode bitfield with
// unsigned content.

template<class T, int shift, int size, class U>
class BitFieldBase {
 public:
  typedef T FieldType;

  // A type U mask of bit field.  To use all bits of a type U of x bits
  // in a bitfield without compiler warnings we have to compute 2^x
  // without using a shift count of x in the computation.
  static const U kOne = static_cast<U>(1U);
  static const U kMask = ((kOne << shift) << size) - (kOne << shift);
  static const U kShift = shift;
  static const U kSize = size;
  static const U kNext = kShift + kSize;
  static const U kNumValues = kOne << size;

  // Value for the field with all bits set.
  static const T kMax = static_cast<T>(kNumValues - 1);

  // Tells whether the provided value fits into the bit field.
  static constexpr bool is_valid(T value) {
    return (static_cast<U>(value) & ~static_cast<U>(kMax)) == 0;
  }

  // Returns a type U with the bit field value encoded.
  static constexpr U encode(T value) {
#if V8_CAN_HAVE_DCHECK_IN_CONSTEXPR
    DCHECK(is_valid(value));
#endif
    return static_cast<U>(value) << shift;
  }

  // Returns a type U with the bit field value updated.
  static constexpr U update(U previous, T value) {
    return (previous & ~kMask) | encode(value);
  }

  // Extracts the bit field from the value.
  static constexpr T decode(U value) {
    return static_cast<T>((value & kMask) >> shift);
  }

  STATIC_ASSERT((kNext - 1) / 8 < sizeof(U));
};

template <class T, int shift, int size>
class BitField8 : public BitFieldBase<T, shift, size, uint8_t> {};


template <class T, int shift, int size>
class BitField16 : public BitFieldBase<T, shift, size, uint16_t> {};


template<class T, int shift, int size>
class BitField : public BitFieldBase<T, shift, size, uint32_t> { };


template<class T, int shift, int size>
class BitField64 : public BitFieldBase<T, shift, size, uint64_t> { };

// Helper macros for defining a contiguous sequence of bit fields. Example:
// (backslashes at the ends of respective lines of this multi-line macro
// definition are omitted here to please the compiler)
//
// #define MAP_BIT_FIELD1(V, _)
//   V(IsAbcBit, bool, 1, _)
//   V(IsBcdBit, bool, 1, _)
//   V(CdeBits, int, 5, _)
//   V(DefBits, MutableMode, 1, _)
//
// DEFINE_BIT_FIELDS(MAP_BIT_FIELD1)
// or
// DEFINE_BIT_FIELDS_64(MAP_BIT_FIELD1)
//
#define DEFINE_BIT_FIELD_RANGE_TYPE(Name, Type, Size, _) \
  k##Name##Start, k##Name##End = k##Name##Start + Size - 1,

#define DEFINE_BIT_RANGES(LIST_MACRO)                               \
  struct LIST_MACRO##_Ranges {                                      \
    enum { LIST_MACRO(DEFINE_BIT_FIELD_RANGE_TYPE, _) kBitsCount }; \
  };

#define DEFINE_BIT_FIELD_TYPE(Name, Type, Size, RangesName) \
  typedef BitField<Type, RangesName::k##Name##Start, Size> Name;

#define DEFINE_BIT_FIELD_64_TYPE(Name, Type, Size, RangesName) \
  typedef BitField64<Type, RangesName::k##Name##Start, Size> Name;

#define DEFINE_BIT_FIELDS(LIST_MACRO) \
  DEFINE_BIT_RANGES(LIST_MACRO)       \
  LIST_MACRO(DEFINE_BIT_FIELD_TYPE, LIST_MACRO##_Ranges)

#define DEFINE_BIT_FIELDS_64(LIST_MACRO) \
  DEFINE_BIT_RANGES(LIST_MACRO)          \
  LIST_MACRO(DEFINE_BIT_FIELD_64_TYPE, LIST_MACRO##_Ranges)

// ----------------------------------------------------------------------------
// BitSetComputer is a help template for encoding and decoding information for
// a variable number of items in an array.
//
// To encode boolean data in a smi array you would use:
// typedef BitSetComputer<bool, 1, kSmiValueSize, uint32_t> BoolComputer;
//
template <class T, int kBitsPerItem, int kBitsPerWord, class U>
class BitSetComputer {
 public:
  static const int kItemsPerWord = kBitsPerWord / kBitsPerItem;
  static const int kMask = (1 << kBitsPerItem) - 1;

  // The number of array elements required to embed T information for each item.
  static int word_count(int items) {
    if (items == 0) return 0;
    return (items - 1) / kItemsPerWord + 1;
  }

  // The array index to look at for item.
  static int index(int base_index, int item) {
    return base_index + item / kItemsPerWord;
  }

  // Extract T data for a given item from data.
  static T decode(U data, int item) {
    return static_cast<T>((data >> shift(item)) & kMask);
  }

  // Return the encoding for a store of value for item in previous.
  static U encode(U previous, int item, T value) {
    int shift_value = shift(item);
    int set_bits = (static_cast<int>(value) << shift_value);
    return (previous & ~(kMask << shift_value)) | set_bits;
  }

  static int shift(int item) { return (item % kItemsPerWord) * kBitsPerItem; }
};

// Helper macros for defining a contiguous sequence of field offset constants.
// Example: (backslashes at the ends of respective lines of this multi-line
// macro definition are omitted here to please the compiler)
//
// #define MAP_FIELDS(V)
//   V(kField1Offset, kTaggedSize)
//   V(kField2Offset, kIntSize)
//   V(kField3Offset, kIntSize)
//   V(kField4Offset, kSystemPointerSize)
//   V(kSize, 0)
//
// DEFINE_FIELD_OFFSET_CONSTANTS(HeapObject::kHeaderSize, MAP_FIELDS)
//
#define DEFINE_ONE_FIELD_OFFSET(Name, Size) Name, Name##End = Name + (Size)-1,

#define DEFINE_FIELD_OFFSET_CONSTANTS(StartOffset, LIST_MACRO) \
  enum {                                                       \
    LIST_MACRO##_StartOffset = StartOffset - 1,                \
    LIST_MACRO(DEFINE_ONE_FIELD_OFFSET)                        \
  };

// Size of the field defined by DEFINE_FIELD_OFFSET_CONSTANTS
#define FIELD_SIZE(Name) (Name##End + 1 - Name)

// ----------------------------------------------------------------------------
// Hash function.

static const uint64_t kZeroHashSeed = 0;

// Thomas Wang, Integer Hash Functions.
// http://www.concentric.net/~Ttwang/tech/inthash.htm`
inline uint32_t ComputeUnseededHash(uint32_t key) {
  uint32_t hash = key;
  hash = ~hash + (hash << 15);  // hash = (hash << 15) - hash - 1;
  hash = hash ^ (hash >> 12);
  hash = hash + (hash << 2);
  hash = hash ^ (hash >> 4);
  hash = hash * 2057;  // hash = (hash + (hash << 3)) + (hash << 11);
  hash = hash ^ (hash >> 16);
  return hash & 0x3fffffff;
}

inline uint32_t ComputeLongHash(uint64_t key) {
  uint64_t hash = key;
  hash = ~hash + (hash << 18);  // hash = (hash << 18) - hash - 1;
  hash = hash ^ (hash >> 31);
  hash = hash * 21;  // hash = (hash + (hash << 2)) + (hash << 4);
  hash = hash ^ (hash >> 11);
  hash = hash + (hash << 6);
  hash = hash ^ (hash >> 22);
  return static_cast<uint32_t>(hash & 0x3fffffff);
}

inline uint32_t ComputeSeededHash(uint32_t key, uint64_t seed) {
#ifdef V8_USE_SIPHASH
  return halfsiphash(key, seed);
#else
  return ComputeLongHash(static_cast<uint64_t>(key) ^ seed);
#endif  // V8_USE_SIPHASH
}

inline uint32_t ComputePointerHash(void* ptr) {
  return ComputeUnseededHash(
      static_cast<uint32_t>(reinterpret_cast<intptr_t>(ptr)));
}

inline uint32_t ComputeAddressHash(Address address) {
  return ComputeUnseededHash(static_cast<uint32_t>(address & 0xFFFFFFFFul));
}

// ----------------------------------------------------------------------------
// Miscellaneous

// Memory offset for lower and higher bits in a 64 bit integer.
#if defined(V8_TARGET_LITTLE_ENDIAN)
static const int kInt64LowerHalfMemoryOffset = 0;
static const int kInt64UpperHalfMemoryOffset = 4;
#elif defined(V8_TARGET_BIG_ENDIAN)
static const int kInt64LowerHalfMemoryOffset = 4;
static const int kInt64UpperHalfMemoryOffset = 0;
#endif  // V8_TARGET_LITTLE_ENDIAN

// A static resource holds a static instance that can be reserved in
// a local scope using an instance of Access.  Attempts to re-reserve
// the instance will cause an error.
template <typename T>
class StaticResource {
 public:
  StaticResource() : is_reserved_(false)  {}

 private:
  template <typename S> friend class Access;
  T instance_;
  bool is_reserved_;
};


// Locally scoped access to a static resource.
template <typename T>
class Access {
 public:
  explicit Access(StaticResource<T>* resource)
    : resource_(resource)
    , instance_(&resource->instance_) {
    DCHECK(!resource->is_reserved_);
    resource->is_reserved_ = true;
  }

  ~Access() {
    resource_->is_reserved_ = false;
    resource_ = nullptr;
    instance_ = nullptr;
  }

  T* value()  { return instance_; }
  T* operator -> ()  { return instance_; }

 private:
  StaticResource<T>* resource_;
  T* instance_;
};

// A pointer that can only be set once and doesn't allow NULL values.
template<typename T>
class SetOncePointer {
 public:
  SetOncePointer() = default;

  bool is_set() const { return pointer_ != nullptr; }

  T* get() const {
    DCHECK_NOT_NULL(pointer_);
    return pointer_;
  }

  void set(T* value) {
    DCHECK(pointer_ == nullptr && value != nullptr);
    pointer_ = value;
  }

  T* operator=(T* value) {
    set(value);
    return value;
  }

  bool operator==(std::nullptr_t) const { return pointer_ == nullptr; }
  bool operator!=(std::nullptr_t) const { return pointer_ != nullptr; }

 private:
  T* pointer_ = nullptr;
};


template <typename T, int kSize>
class EmbeddedVector : public Vector<T> {
 public:
  EmbeddedVector() : Vector<T>(buffer_, kSize) { }

  explicit EmbeddedVector(T initial_value) : Vector<T>(buffer_, kSize) {
    for (int i = 0; i < kSize; ++i) {
      buffer_[i] = initial_value;
    }
  }

  // When copying, make underlying Vector to reference our buffer.
  EmbeddedVector(const EmbeddedVector& rhs) V8_NOEXCEPT : Vector<T>(rhs) {
    MemCopy(buffer_, rhs.buffer_, sizeof(T) * kSize);
    this->set_start(buffer_);
  }

  EmbeddedVector& operator=(const EmbeddedVector& rhs) V8_NOEXCEPT {
    if (this == &rhs) return *this;
    Vector<T>::operator=(rhs);
    MemCopy(buffer_, rhs.buffer_, sizeof(T) * kSize);
    this->set_start(buffer_);
    return *this;
  }

 private:
  T buffer_[kSize];
};

// Compare 8bit/16bit chars to 8bit/16bit chars.
template <typename lchar, typename rchar>
inline int CompareCharsUnsigned(const lchar* lhs, const rchar* rhs,
                                size_t chars) {
  const lchar* limit = lhs + chars;
  if (sizeof(*lhs) == sizeof(char) && sizeof(*rhs) == sizeof(char)) {
    // memcmp compares byte-by-byte, yielding wrong results for two-byte
    // strings on little-endian systems.
    return memcmp(lhs, rhs, chars);
  }
  while (lhs < limit) {
    int r = static_cast<int>(*lhs) - static_cast<int>(*rhs);
    if (r != 0) return r;
    ++lhs;
    ++rhs;
  }
  return 0;
}

template <typename lchar, typename rchar>
inline int CompareChars(const lchar* lhs, const rchar* rhs, size_t chars) {
  DCHECK_LE(sizeof(lchar), 2);
  DCHECK_LE(sizeof(rchar), 2);
  if (sizeof(lchar) == 1) {
    if (sizeof(rchar) == 1) {
      return CompareCharsUnsigned(reinterpret_cast<const uint8_t*>(lhs),
                                  reinterpret_cast<const uint8_t*>(rhs),
                                  chars);
    } else {
      return CompareCharsUnsigned(reinterpret_cast<const uint8_t*>(lhs),
                                  reinterpret_cast<const uint16_t*>(rhs),
                                  chars);
    }
  } else {
    if (sizeof(rchar) == 1) {
      return CompareCharsUnsigned(reinterpret_cast<const uint16_t*>(lhs),
                                  reinterpret_cast<const uint8_t*>(rhs),
                                  chars);
    } else {
      return CompareCharsUnsigned(reinterpret_cast<const uint16_t*>(lhs),
                                  reinterpret_cast<const uint16_t*>(rhs),
                                  chars);
    }
  }
}


// Calculate 10^exponent.
inline int TenToThe(int exponent) {
  DCHECK_LE(exponent, 9);
  DCHECK_GE(exponent, 1);
  int answer = 10;
  for (int i = 1; i < exponent; i++) answer *= 10;
  return answer;
}


template<typename ElementType, int NumElements>
class EmbeddedContainer {
 public:
  EmbeddedContainer() : elems_() { }

  int length() const { return NumElements; }
  const ElementType& operator[](int i) const {
    DCHECK(i < length());
    return elems_[i];
  }
  ElementType& operator[](int i) {
    DCHECK(i < length());
    return elems_[i];
  }

 private:
  ElementType elems_[NumElements];
};


template<typename ElementType>
class EmbeddedContainer<ElementType, 0> {
 public:
  int length() const { return 0; }
  const ElementType& operator[](int i) const {
    UNREACHABLE();
    static ElementType t = 0;
    return t;
  }
  ElementType& operator[](int i) {
    UNREACHABLE();
    static ElementType t = 0;
    return t;
  }
};


// Helper class for building result strings in a character buffer. The
// purpose of the class is to use safe operations that checks the
// buffer bounds on all operations in debug mode.
// This simple base class does not allow formatted output.
class SimpleStringBuilder {
 public:
  // Create a string builder with a buffer of the given size. The
  // buffer is allocated through NewArray<char> and must be
  // deallocated by the caller of Finalize().
  explicit SimpleStringBuilder(int size);

  SimpleStringBuilder(char* buffer, int size)
      : buffer_(buffer, size), position_(0) { }

  ~SimpleStringBuilder() { if (!is_finalized()) Finalize(); }

  int size() const { return buffer_.length(); }

  // Get the current position in the builder.
  int position() const {
    DCHECK(!is_finalized());
    return position_;
  }

  // Reset the position.
  void Reset() { position_ = 0; }

  // Add a single character to the builder. It is not allowed to add
  // 0-characters; use the Finalize() method to terminate the string
  // instead.
  void AddCharacter(char c) {
    DCHECK_NE(c, '\0');
    DCHECK(!is_finalized() && position_ < buffer_.length());
    buffer_[position_++] = c;
  }

  // Add an entire string to the builder. Uses strlen() internally to
  // compute the length of the input string.
  void AddString(const char* s);

  // Add the first 'n' characters of the given 0-terminated string 's' to the
  // builder. The input string must have enough characters.
  void AddSubstring(const char* s, int n);

  // Add character padding to the builder. If count is non-positive,
  // nothing is added to the builder.
  void AddPadding(char c, int count);

  // Add the decimal representation of the value.
  void AddDecimalInteger(int value);

  // Finalize the string by 0-terminating it and returning the buffer.
  char* Finalize();

 protected:
  Vector<char> buffer_;
  int position_;

  bool is_finalized() const { return position_ < 0; }

 private:
  DISALLOW_IMPLICIT_CONSTRUCTORS(SimpleStringBuilder);
};

// Bit field extraction.
inline uint32_t unsigned_bitextract_32(int msb, int lsb, uint32_t x) {
  return (x >> lsb) & ((1 << (1 + msb - lsb)) - 1);
}

inline uint64_t unsigned_bitextract_64(int msb, int lsb, uint64_t x) {
  return (x >> lsb) & ((static_cast<uint64_t>(1) << (1 + msb - lsb)) - 1);
}

inline int32_t signed_bitextract_32(int msb, int lsb, int32_t x) {
  return (x << (31 - msb)) >> (lsb + 31 - msb);
}

inline int signed_bitextract_64(int msb, int lsb, int x) {
  // TODO(jbramley): This is broken for big bitfields.
  return (x << (63 - msb)) >> (lsb + 63 - msb);
}

// Check number width.
inline bool is_intn(int64_t x, unsigned n) {
  DCHECK((0 < n) && (n < 64));
  int64_t limit = static_cast<int64_t>(1) << (n - 1);
  return (-limit <= x) && (x < limit);
}

inline bool is_uintn(int64_t x, unsigned n) {
  DCHECK((0 < n) && (n < (sizeof(x) * kBitsPerByte)));
  return !(x >> n);
}

template <class T>
inline T truncate_to_intn(T x, unsigned n) {
  DCHECK((0 < n) && (n < (sizeof(x) * kBitsPerByte)));
  return (x & ((static_cast<T>(1) << n) - 1));
}

#define INT_1_TO_63_LIST(V)                                                    \
V(1)  V(2)  V(3)  V(4)  V(5)  V(6)  V(7)  V(8)                                 \
V(9)  V(10) V(11) V(12) V(13) V(14) V(15) V(16)                                \
V(17) V(18) V(19) V(20) V(21) V(22) V(23) V(24)                                \
V(25) V(26) V(27) V(28) V(29) V(30) V(31) V(32)                                \
V(33) V(34) V(35) V(36) V(37) V(38) V(39) V(40)                                \
V(41) V(42) V(43) V(44) V(45) V(46) V(47) V(48)                                \
V(49) V(50) V(51) V(52) V(53) V(54) V(55) V(56)                                \
V(57) V(58) V(59) V(60) V(61) V(62) V(63)

#define DECLARE_IS_INT_N(N)                                                    \
inline bool is_int##N(int64_t x) { return is_intn(x, N); }
#define DECLARE_IS_UINT_N(N)                                                   \
template <class T>                                                             \
inline bool is_uint##N(T x) { return is_uintn(x, N); }
#define DECLARE_TRUNCATE_TO_INT_N(N)                                           \
template <class T>                                                             \
inline T truncate_to_int##N(T x) { return truncate_to_intn(x, N); }
INT_1_TO_63_LIST(DECLARE_IS_INT_N)
INT_1_TO_63_LIST(DECLARE_IS_UINT_N)
INT_1_TO_63_LIST(DECLARE_TRUNCATE_TO_INT_N)
#undef DECLARE_IS_INT_N
#undef DECLARE_IS_UINT_N
#undef DECLARE_TRUNCATE_TO_INT_N

// clang-format off
#define INT_0_TO_127_LIST(V)                                          \
V(0)   V(1)   V(2)   V(3)   V(4)   V(5)   V(6)   V(7)   V(8)   V(9)   \
V(10)  V(11)  V(12)  V(13)  V(14)  V(15)  V(16)  V(17)  V(18)  V(19)  \
V(20)  V(21)  V(22)  V(23)  V(24)  V(25)  V(26)  V(27)  V(28)  V(29)  \
V(30)  V(31)  V(32)  V(33)  V(34)  V(35)  V(36)  V(37)  V(38)  V(39)  \
V(40)  V(41)  V(42)  V(43)  V(44)  V(45)  V(46)  V(47)  V(48)  V(49)  \
V(50)  V(51)  V(52)  V(53)  V(54)  V(55)  V(56)  V(57)  V(58)  V(59)  \
V(60)  V(61)  V(62)  V(63)  V(64)  V(65)  V(66)  V(67)  V(68)  V(69)  \
V(70)  V(71)  V(72)  V(73)  V(74)  V(75)  V(76)  V(77)  V(78)  V(79)  \
V(80)  V(81)  V(82)  V(83)  V(84)  V(85)  V(86)  V(87)  V(88)  V(89)  \
V(90)  V(91)  V(92)  V(93)  V(94)  V(95)  V(96)  V(97)  V(98)  V(99)  \
V(100) V(101) V(102) V(103) V(104) V(105) V(106) V(107) V(108) V(109) \
V(110) V(111) V(112) V(113) V(114) V(115) V(116) V(117) V(118) V(119) \
V(120) V(121) V(122) V(123) V(124) V(125) V(126) V(127)
// clang-format on

class FeedbackSlot {
 public:
  FeedbackSlot() : id_(kInvalidSlot) {}
  explicit FeedbackSlot(int id) : id_(id) {}

  int ToInt() const { return id_; }

  static FeedbackSlot Invalid() { return FeedbackSlot(); }
  bool IsInvalid() const { return id_ == kInvalidSlot; }

  bool operator==(FeedbackSlot that) const { return this->id_ == that.id_; }
  bool operator!=(FeedbackSlot that) const { return !(*this == that); }

  friend size_t hash_value(FeedbackSlot slot) { return slot.ToInt(); }
  friend std::ostream& operator<<(std::ostream& os, FeedbackSlot);

 private:
  static const int kInvalidSlot = -1;

  int id_;
};


class BailoutId {
 public:
  explicit BailoutId(int id) : id_(id) { }
  int ToInt() const { return id_; }

  static BailoutId None() { return BailoutId(kNoneId); }
  static BailoutId ScriptContext() { return BailoutId(kScriptContextId); }
  static BailoutId FunctionContext() { return BailoutId(kFunctionContextId); }
  static BailoutId FunctionEntry() { return BailoutId(kFunctionEntryId); }
  static BailoutId Declarations() { return BailoutId(kDeclarationsId); }
  static BailoutId FirstUsable() { return BailoutId(kFirstUsableId); }
  static BailoutId StubEntry() { return BailoutId(kStubEntryId); }

  // Special bailout id support for deopting into the {JSConstructStub} stub.
  // The following hard-coded deoptimization points are supported by the stub:
  //  - {ConstructStubCreate} maps to {construct_stub_create_deopt_pc_offset}.
  //  - {ConstructStubInvoke} maps to {construct_stub_invoke_deopt_pc_offset}.
  static BailoutId ConstructStubCreate() { return BailoutId(1); }
  static BailoutId ConstructStubInvoke() { return BailoutId(2); }
  bool IsValidForConstructStub() const {
    return id_ == ConstructStubCreate().ToInt() ||
           id_ == ConstructStubInvoke().ToInt();
  }

  bool IsNone() const { return id_ == kNoneId; }
  bool operator==(const BailoutId& other) const { return id_ == other.id_; }
  bool operator!=(const BailoutId& other) const { return id_ != other.id_; }
  friend size_t hash_value(BailoutId);
  V8_EXPORT_PRIVATE friend std::ostream& operator<<(std::ostream&, BailoutId);

 private:
  friend class Builtins;

  static const int kNoneId = -1;

  // Using 0 could disguise errors.
  static const int kScriptContextId = 1;
  static const int kFunctionContextId = 2;
  static const int kFunctionEntryId = 3;

  // This AST id identifies the point after the declarations have been visited.
  // We need it to capture the environment effects of declarations that emit
  // code (function declarations).
  static const int kDeclarationsId = 4;

  // Every FunctionState starts with this id.
  static const int kFirstUsableId = 5;

  // Every compiled stub starts with this id.
  static const int kStubEntryId = 6;

  // Builtin continuations bailout ids start here. If you need to add a
  // non-builtin BailoutId, add it before this id so that this Id has the
  // highest number.
  static const int kFirstBuiltinContinuationId = 7;

  int id_;
};


// ----------------------------------------------------------------------------
// I/O support.

// Our version of printf().
V8_EXPORT_PRIVATE void PRINTF_FORMAT(1, 2) PrintF(const char* format, ...);
void PRINTF_FORMAT(2, 3) PrintF(FILE* out, const char* format, ...);

// Prepends the current process ID to the output.
void PRINTF_FORMAT(1, 2) PrintPID(const char* format, ...);

// Prepends the current process ID and given isolate pointer to the output.
void PRINTF_FORMAT(2, 3) PrintIsolate(void* isolate, const char* format, ...);

// Safe formatting print. Ensures that str is always null-terminated.
// Returns the number of chars written, or -1 if output was truncated.
int PRINTF_FORMAT(2, 3) SNPrintF(Vector<char> str, const char* format, ...);
V8_EXPORT_PRIVATE int PRINTF_FORMAT(2, 0)
    VSNPrintF(Vector<char> str, const char* format, va_list args);

void StrNCpy(Vector<char> dest, const char* src, size_t n);

// Our version of fflush.
void Flush(FILE* out);

inline void Flush() {
  Flush(stdout);
}


// Read a line of characters after printing the prompt to stdout. The resulting
// char* needs to be disposed off with DeleteArray by the caller.
char* ReadLine(const char* prompt);


// Append size chars from str to the file given by filename.
// The file is overwritten. Returns the number of chars written.
int AppendChars(const char* filename,
                const char* str,
                int size,
                bool verbose = true);


// Write size chars from str to the file given by filename.
// The file is overwritten. Returns the number of chars written.
int WriteChars(const char* filename,
               const char* str,
               int size,
               bool verbose = true);


// Write size bytes to the file given by filename.
// The file is overwritten. Returns the number of bytes written.
int WriteBytes(const char* filename,
               const byte* bytes,
               int size,
               bool verbose = true);


// Write the C code
// const char* <varname> = "<str>";
// const int <varname>_len = <len>;
// to the file given by filename. Only the first len chars are written.
int WriteAsCFile(const char* filename, const char* varname,
                 const char* str, int size, bool verbose = true);


// Simple support to read a file into std::string.
// On return, *exits tells whether the file existed.
V8_EXPORT_PRIVATE std::string ReadFile(const char* filename, bool* exists,
                                       bool verbose = true);
std::string ReadFile(FILE* file, bool* exists, bool verbose = true);

class StringBuilder : public SimpleStringBuilder {
 public:
  explicit StringBuilder(int size) : SimpleStringBuilder(size) { }
  StringBuilder(char* buffer, int size) : SimpleStringBuilder(buffer, size) { }

  // Add formatted contents to the builder just like printf().
  void PRINTF_FORMAT(2, 3) AddFormatted(const char* format, ...);

  // Add formatted contents like printf based on a va_list.
  void PRINTF_FORMAT(2, 0) AddFormattedList(const char* format, va_list list);

 private:
  DISALLOW_IMPLICIT_CONSTRUCTORS(StringBuilder);
};


bool DoubleToBoolean(double d);

template <typename Char>
bool TryAddIndexChar(uint32_t* index, Char c);

template <typename Stream>
bool StringToArrayIndex(Stream* stream, uint32_t* index);

// Returns the current stack top. Works correctly with ASAN and SafeStack.
// GetCurrentStackPosition() should not be inlined, because it works on stack
// frames if it were inlined into a function with a huge stack frame it would
// return an address significantly above the actual current stack position.
V8_NOINLINE uintptr_t GetCurrentStackPosition();

template <typename V>
static inline V ByteReverse(V value) {
  size_t size_of_v = sizeof(value);
  switch (size_of_v) {
    case 2:
#if V8_HAS_BUILTIN_BSWAP16
      return static_cast<V>(__builtin_bswap16(static_cast<uint16_t>(value)));
#else
      return value << 8 | (value >> 8 & 0x00FF);
#endif
    case 4:
#if V8_HAS_BUILTIN_BSWAP32
      return static_cast<V>(__builtin_bswap32(static_cast<uint32_t>(value)));
#else
    {
      size_t bits_of_v = size_of_v * kBitsPerByte;
      return value << (bits_of_v - 8) |
             ((value << (bits_of_v - 24)) & 0x00FF0000) |
             ((value >> (bits_of_v - 24)) & 0x0000FF00) |
             ((value >> (bits_of_v - 8)) & 0x00000FF);
    }
#endif
    case 8:
#if V8_HAS_BUILTIN_BSWAP64
      return static_cast<V>(__builtin_bswap64(static_cast<uint64_t>(value)));
#else
    {
      size_t bits_of_v = size_of_v * kBitsPerByte;
      return value << (bits_of_v - 8) |
             ((value << (bits_of_v - 24)) & 0x00FF000000000000) |
             ((value << (bits_of_v - 40)) & 0x0000FF0000000000) |
             ((value << (bits_of_v - 56)) & 0x000000FF00000000) |
             ((value >> (bits_of_v - 56)) & 0x00000000FF000000) |
             ((value >> (bits_of_v - 40)) & 0x0000000000FF0000) |
             ((value >> (bits_of_v - 24)) & 0x000000000000FF00) |
             ((value >> (bits_of_v - 8)) & 0x00000000000000FF);
    }
#endif
    default:
      UNREACHABLE();
  }
}

V8_EXPORT_PRIVATE bool PassesFilter(Vector<const char> name,
                                    Vector<const char> filter);

// Zap the specified area with a specific byte pattern. This currently defaults
// to int3 on x64 and ia32. On other architectures this will produce unspecified
// instruction sequences.
// TODO(jgruber): Better support for other architectures.
V8_INLINE void ZapCode(Address addr, size_t size_in_bytes) {
  static constexpr int kZapByte = 0xCC;
  std::memset(reinterpret_cast<void*>(addr), kZapByte, size_in_bytes);
}

}  // namespace internal
}  // namespace v8

#endif  // V8_UTILS_H_