path: root/deps/v8/src/base/bits.h

// Copyright 2014 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_BASE_BITS_H_
#define V8_BASE_BITS_H_

#include <stdint.h>
#include <type_traits>

#include "src/base/base-export.h"
#include "src/base/macros.h"
#if V8_CC_MSVC
#include <intrin.h>
#endif
#if V8_OS_WIN32
#include "src/base/win32-headers.h"
#endif

namespace v8 {
namespace base {

namespace internal {
template <typename T>
class CheckedNumeric;
}

namespace bits {

// Define overloaded |Name| for |Name32| and |Name64|, depending on the size of
// the given value.
//
// The overloads are only defined for input types of size 4 and 8, respectively,
// using enable_if and SFINAE to disable them otherwise. enable_if<bool,
// typename> only has a "type" member if the first parameter is true, in which
// case "type" is a typedef to the second member (here, set to "unsigned").
// Otherwise, enable_if::type doesn't exist, making the function signature
// invalid, and so the entire function is thrown away (without an error) due to
// SFINAE.
//
// Not that we cannot simply check sizeof(T) using an if statement, as we need
// both branches of the if to be syntactically valid even if one of the branches
// is dead.
#define DEFINE_32_64_OVERLOADS(Name)                                   \
  template <typename T>                                                \
  inline typename std::enable_if<sizeof(T) == 4, unsigned>::type Name( \
      T value) {                                                       \
    return Name##32(value);                                            \
  }                                                                    \
                                                                       \
  template <typename T>                                                \
  inline typename std::enable_if<sizeof(T) == 8, unsigned>::type Name( \
      T value) {                                                       \
    return Name##64(value);                                            \
  }

// CountPopulation32(value) returns the number of bits set in |value|.
inline unsigned CountPopulation32(uint32_t value) {
#if V8_HAS_BUILTIN_POPCOUNT
  return __builtin_popcount(value);
#else
  value = ((value >> 1) & 0x55555555) + (value & 0x55555555);
  value = ((value >> 2) & 0x33333333) + (value & 0x33333333);
  value = ((value >> 4) & 0x0f0f0f0f) + (value & 0x0f0f0f0f);
  value = ((value >> 8) & 0x00ff00ff) + (value & 0x00ff00ff);
  value = ((value >> 16) & 0x0000ffff) + (value & 0x0000ffff);
  return static_cast<unsigned>(value);
#endif
}


// CountPopulation64(value) returns the number of bits set in |value|.
inline unsigned CountPopulation64(uint64_t value) {
#if V8_HAS_BUILTIN_POPCOUNT
  return __builtin_popcountll(value);
#else
  return CountPopulation32(static_cast<uint32_t>(value)) +
         CountPopulation32(static_cast<uint32_t>(value >> 32));
#endif
}

DEFINE_32_64_OVERLOADS(CountPopulation)

// CountLeadingZeros32(value) returns the number of zero bits following the most
// significant 1 bit in |value| if |value| is non-zero, otherwise it returns 32.
inline unsigned CountLeadingZeros32(uint32_t value) {
#if V8_HAS_BUILTIN_CLZ
  return value ? __builtin_clz(value) : 32;
#elif V8_CC_MSVC
  unsigned long result;  // NOLINT(runtime/int)
  if (!_BitScanReverse(&result, value)) return 32;
  return static_cast<unsigned>(31 - result);
#else
  value = value | (value >> 1);
  value = value | (value >> 2);
  value = value | (value >> 4);
  value = value | (value >> 8);
  value = value | (value >> 16);
  return CountPopulation32(~value);
#endif
}


// CountLeadingZeros64(value) returns the number of zero bits following the most
// significant 1 bit in |value| if |value| is non-zero, otherwise it returns 64.
inline unsigned CountLeadingZeros64(uint64_t value) {
#if V8_HAS_BUILTIN_CLZ
  return value ? __builtin_clzll(value) : 64;
#else
  value = value | (value >> 1);
  value = value | (value >> 2);
  value = value | (value >> 4);
  value = value | (value >> 8);
  value = value | (value >> 16);
  value = value | (value >> 32);
  return CountPopulation64(~value);
#endif
}

DEFINE_32_64_OVERLOADS(CountLeadingZeros)

// ReverseBits(value) returns |value| in reverse bit order.
template <typename T>
T ReverseBits(T value) {
  DCHECK((sizeof(value) == 1) || (sizeof(value) == 2) || (sizeof(value) == 4) ||
         (sizeof(value) == 8));
  T result = 0;
  for (unsigned i = 0; i < (sizeof(value) * 8); i++) {
    result = (result << 1) | (value & 1);
    value >>= 1;
  }
  return result;
}

// CountTrailingZeros32(value) returns the number of zero bits preceding the
// least significant 1 bit in |value| if |value| is non-zero, otherwise it
// returns 32.
inline unsigned CountTrailingZeros32(uint32_t value) {
#if V8_HAS_BUILTIN_CTZ
  return value ? __builtin_ctz(value) : 32;
#elif V8_CC_MSVC
  unsigned long result;  // NOLINT(runtime/int)
  if (!_BitScanForward(&result, value)) return 32;
  return static_cast<unsigned>(result);
#else
  if (value == 0) return 32;
  unsigned count = 0;
  for (value ^= value - 1; value >>= 1; ++count) {
  }
  return count;
#endif
}


// CountTrailingZeros64(value) returns the number of zero bits preceding the
// least significant 1 bit in |value| if |value| is non-zero, otherwise it
// returns 64.
inline unsigned CountTrailingZeros64(uint64_t value) {
#if V8_HAS_BUILTIN_CTZ
  return value ? __builtin_ctzll(value) : 64;
#else
  if (value == 0) return 64;
  unsigned count = 0;
  for (value ^= value - 1; value >>= 1; ++count) {
  }
  return count;
#endif
}

DEFINE_32_64_OVERLOADS(CountTrailingZeros)

// Returns true iff |value| is a power of 2.
template <typename T,
          typename = typename std::enable_if<std::is_integral<T>::value>::type>
constexpr inline bool IsPowerOfTwo(T value) {
  return value > 0 && (value & (value - 1)) == 0;
}

// RoundUpToPowerOfTwo32(value) returns the smallest power of two which is
// greater than or equal to |value|. If you pass in a |value| that is already a
// power of two, it is returned as is. |value| must be less than or equal to
// 0x80000000u. Uses computation based on leading zeros if we have compiler
// support for that. Falls back to the implementation from "Hacker's Delight" by
// Henry S. Warren, Jr., figure 3-3, page 48, where the function is called clp2.
V8_BASE_EXPORT uint32_t RoundUpToPowerOfTwo32(uint32_t value);
// Same for 64 bit integers. |value| must be <= 2^63
V8_BASE_EXPORT uint64_t RoundUpToPowerOfTwo64(uint64_t value);

// RoundDownToPowerOfTwo32(value) returns the greatest power of two which is
// less than or equal to |value|. If you pass in a |value| that is already a
// power of two, it is returned as is.
inline uint32_t RoundDownToPowerOfTwo32(uint32_t value) {
  if (value > 0x80000000u) return 0x80000000u;
  uint32_t result = RoundUpToPowerOfTwo32(value);
  if (result > value) result >>= 1;
  return result;
}


// Precondition: 0 <= shift < 32
inline uint32_t RotateRight32(uint32_t value, uint32_t shift) {
  if (shift == 0) return value;
  return (value >> shift) | (value << (32 - shift));
}

// Precondition: 0 <= shift < 32
inline uint32_t RotateLeft32(uint32_t value, uint32_t shift) {
  if (shift == 0) return value;
  return (value << shift) | (value >> (32 - shift));
}

// Precondition: 0 <= shift < 64
inline uint64_t RotateRight64(uint64_t value, uint64_t shift) {
  if (shift == 0) return value;
  return (value >> shift) | (value << (64 - shift));
}

// Precondition: 0 <= shift < 64
inline uint64_t RotateLeft64(uint64_t value, uint64_t shift) {
  if (shift == 0) return value;
  return (value << shift) | (value >> (64 - shift));
}


// SignedAddOverflow32(lhs,rhs,val) performs a signed summation of |lhs| and
// |rhs| and stores the result into the variable pointed to by |val| and
// returns true if the signed summation resulted in an overflow.
inline bool SignedAddOverflow32(int32_t lhs, int32_t rhs, int32_t* val) {
#if V8_HAS_BUILTIN_SADD_OVERFLOW
  return __builtin_sadd_overflow(lhs, rhs, val);
#else
  uint32_t res = static_cast<uint32_t>(lhs) + static_cast<uint32_t>(rhs);
  *val = bit_cast<int32_t>(res);
  return ((res ^ lhs) & (res ^ rhs) & (1U << 31)) != 0;
#endif
}


// SignedSubOverflow32(lhs,rhs,val) performs a signed subtraction of |lhs| and
// |rhs| and stores the result into the variable pointed to by |val| and
// returns true if the signed subtraction resulted in an overflow.
inline bool SignedSubOverflow32(int32_t lhs, int32_t rhs, int32_t* val) {
#if V8_HAS_BUILTIN_SSUB_OVERFLOW
  return __builtin_ssub_overflow(lhs, rhs, val);
#else
  uint32_t res = static_cast<uint32_t>(lhs) - static_cast<uint32_t>(rhs);
  *val = bit_cast<int32_t>(res);
  return ((res ^ lhs) & (res ^ ~rhs) & (1U << 31)) != 0;
#endif
}

// SignedMulOverflow32(lhs,rhs,val) performs a signed multiplication of |lhs|
// and |rhs| and stores the result into the variable pointed to by |val| and
// returns true if the signed multiplication resulted in an overflow.
V8_BASE_EXPORT bool SignedMulOverflow32(int32_t lhs, int32_t rhs, int32_t* val);

// SignedAddOverflow64(lhs,rhs,val) performs a signed summation of |lhs| and
// |rhs| and stores the result into the variable pointed to by |val| and
// returns true if the signed summation resulted in an overflow.
inline bool SignedAddOverflow64(int64_t lhs, int64_t rhs, int64_t* val) {
  uint64_t res = static_cast<uint64_t>(lhs) + static_cast<uint64_t>(rhs);
  *val = bit_cast<int64_t>(res);
  return ((res ^ lhs) & (res ^ rhs) & (1ULL << 63)) != 0;
}


// SignedSubOverflow64(lhs,rhs,val) performs a signed subtraction of |lhs| and
// |rhs| and stores the result into the variable pointed to by |val| and
// returns true if the signed subtraction resulted in an overflow.
inline bool SignedSubOverflow64(int64_t lhs, int64_t rhs, int64_t* val) {
  uint64_t res = static_cast<uint64_t>(lhs) - static_cast<uint64_t>(rhs);
  *val = bit_cast<int64_t>(res);
  return ((res ^ lhs) & (res ^ ~rhs) & (1ULL << 63)) != 0;
}

// SignedMulOverflow64(lhs,rhs,val) performs a signed multiplication of |lhs|
// and |rhs| and stores the result into the variable pointed to by |val| and
// returns true if the signed multiplication resulted in an overflow.
V8_BASE_EXPORT bool SignedMulOverflow64(int64_t lhs, int64_t rhs, int64_t* val);

// SignedMulHigh32(lhs, rhs) multiplies two signed 32-bit values |lhs| and
// |rhs|, extracts the most significant 32 bits of the result, and returns
// those.
V8_BASE_EXPORT int32_t SignedMulHigh32(int32_t lhs, int32_t rhs);

// SignedMulHighAndAdd32(lhs, rhs, acc) multiplies two signed 32-bit values
// |lhs| and |rhs|, extracts the most significant 32 bits of the result, and
// adds the accumulate value |acc|.
V8_BASE_EXPORT int32_t SignedMulHighAndAdd32(int32_t lhs, int32_t rhs,
                                             int32_t acc);

// SignedDiv32(lhs, rhs) divides |lhs| by |rhs| and returns the quotient
// truncated to int32. If |rhs| is zero, then zero is returned. If |lhs|
// is minint and |rhs| is -1, it returns minint.
V8_BASE_EXPORT int32_t SignedDiv32(int32_t lhs, int32_t rhs);

// SignedMod32(lhs, rhs) divides |lhs| by |rhs| and returns the remainder
// truncated to int32. If either |rhs| is zero or |lhs| is minint and |rhs|
// is -1, it returns zero.
V8_BASE_EXPORT int32_t SignedMod32(int32_t lhs, int32_t rhs);

// UnsignedAddOverflow32(lhs,rhs,val) performs an unsigned summation of |lhs|
// and |rhs| and stores the result into the variable pointed to by |val| and
// returns true if the unsigned summation resulted in an overflow.
inline bool UnsignedAddOverflow32(uint32_t lhs, uint32_t rhs, uint32_t* val) {
#if V8_HAS_BUILTIN_SADD_OVERFLOW
  return __builtin_uadd_overflow(lhs, rhs, val);
#else
  *val = lhs + rhs;
  return *val < (lhs | rhs);
#endif
}


// UnsignedDiv32(lhs, rhs) divides |lhs| by |rhs| and returns the quotient
// truncated to uint32. If |rhs| is zero, then zero is returned.
inline uint32_t UnsignedDiv32(uint32_t lhs, uint32_t rhs) {
  return rhs ? lhs / rhs : 0u;
}


// UnsignedMod32(lhs, rhs) divides |lhs| by |rhs| and returns the remainder
// truncated to uint32. If |rhs| is zero, then zero is returned.
inline uint32_t UnsignedMod32(uint32_t lhs, uint32_t rhs) {
  return rhs ? lhs % rhs : 0u;
}


// Clamp |value| on overflow and underflow conditions.
V8_BASE_EXPORT int64_t
FromCheckedNumeric(const internal::CheckedNumeric<int64_t> value);

// SignedSaturatedAdd64(lhs, rhs) adds |lhs| and |rhs|,
// checks and returns the result.
V8_BASE_EXPORT int64_t SignedSaturatedAdd64(int64_t lhs, int64_t rhs);

// SignedSaturatedSub64(lhs, rhs) subtracts |lhs| by |rhs|,
// checks and returns the result.
V8_BASE_EXPORT int64_t SignedSaturatedSub64(int64_t lhs, int64_t rhs);

#undef DEFINE_32_64_OVERLOADS

}  // namespace bits
}  // namespace base
}  // namespace v8

#endif  // V8_BASE_BITS_H_