double-conversion / src / bignum.h

Florian Loitsch 8743711 


























Florian Loitsch e6eb529 

Florian Loitsch 8743711 
Florian Loitsch e6eb529 


Florian Loitsch 8743711 





































Florian Loitsch baa5675 



Florian Loitsch 8743711 
















































Florian Loitsch e6eb529 
Florian Loitsch 8743711 
















Florian Loitsch e6eb529 
Florian Loitsch 8743711 
Florian Loitsch e6eb529 
// Copyright 2010 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
//       copyright notice, this list of conditions and the following
//       disclaimer in the documentation and/or other materials provided
//       with the distribution.
//     * Neither the name of Google Inc. nor the names of its
//       contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#ifndef DOUBLE_CONVERSION_BIGNUM_H_
#define DOUBLE_CONVERSION_BIGNUM_H_

#include "utils.h"

namespace double_conversion {

class Bignum {
 public:
  // 3584 = 128 * 28. We can represent 2^3584 > 10^1000 accurately.
  // This bignum can encode much bigger numbers, since it contains an
  // exponent.
  static const int kMaxSignificantBits = 3584;

  Bignum();
  void AssignUInt16(uint16_t value);
  void AssignUInt64(uint64_t value);
  void AssignBignum(const Bignum& other);

  void AssignDecimalString(Vector<const char> value);
  void AssignHexString(Vector<const char> value);

  void AssignPowerUInt16(uint16_t base, int exponent);

  void AddUInt16(uint16_t operand);
  void AddUInt64(uint64_t operand);
  void AddBignum(const Bignum& other);
  // Precondition: this >= other.
  void SubtractBignum(const Bignum& other);

  void Square();
  void ShiftLeft(int shift_amount);
  void MultiplyByUInt32(uint32_t factor);
  void MultiplyByUInt64(uint64_t factor);
  void MultiplyByPowerOfTen(int exponent);
  void Times10() { return MultiplyByUInt32(10); }
  // Pseudocode:
  //  int result = this / other;
  //  this = this % other;
  // In the worst case this function is in O(this/other).
  uint16_t DivideModuloIntBignum(const Bignum& other);

  bool ToHexString(char* buffer, int buffer_size) const;

  // Returns
  //  -1 if a < b,
  //   0 if a == b, and
  //  +1 if a > b.
  static int Compare(const Bignum& a, const Bignum& b);
  static bool Equal(const Bignum& a, const Bignum& b) {
    return Compare(a, b) == 0;
  }
  static bool LessEqual(const Bignum& a, const Bignum& b) {
    return Compare(a, b) <= 0;
  }
  static bool Less(const Bignum& a, const Bignum& b) {
    return Compare(a, b) < 0;
  }
  // Returns Compare(a + b, c);
  static int PlusCompare(const Bignum& a, const Bignum& b, const Bignum& c);
  // Returns a + b == c
  static bool PlusEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
    return PlusCompare(a, b, c) == 0;
  }
  // Returns a + b <= c
  static bool PlusLessEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
    return PlusCompare(a, b, c) <= 0;
  }
  // Returns a + b < c
  static bool PlusLess(const Bignum& a, const Bignum& b, const Bignum& c) {
    return PlusCompare(a, b, c) < 0;
  }
 private:
  typedef uint32_t Chunk;
  typedef uint64_t DoubleChunk;

  static const int kChunkSize = sizeof(Chunk) * 8;
  static const int kDoubleChunkSize = sizeof(DoubleChunk) * 8;
  // With bigit size of 28 we loose some bits, but a double still fits easily
  // into two chunks, and more importantly we can use the Comba multiplication.
  static const int kBigitSize = 28;
  static const Chunk kBigitMask = (1 << kBigitSize) - 1;
  // Every instance allocates kBigitLength chunks on the stack. Bignums cannot
  // grow. There are no checks if the stack-allocated space is sufficient.
  static const int kBigitCapacity = kMaxSignificantBits / kBigitSize;

  void EnsureCapacity(int size) {
    if (size > kBigitCapacity) {
      UNREACHABLE();
    }
  }
  void Align(const Bignum& other);
  void Clamp();
  bool IsClamped() const;
  void Zero();
  // Requires this to have enough capacity (no tests done).
  // Updates used_digits_ if necessary.
  // shift_amount must be < kBigitSize.
  void BigitsShiftLeft(int shift_amount);
  // BigitLength includes the "hidden" digits encoded in the exponent.
  int BigitLength() const { return used_digits_ + exponent_; }
  Chunk BigitAt(int index) const;
  void SubtractTimes(const Bignum& other, int factor);

  Chunk bigits_buffer_[kBigitCapacity];
  // A vector backed by bigits_buffer_. This way accesses to the array are
  // checked for out-of-bounds errors.
  Vector<Chunk> bigits_;
  int used_digits_;
  // The Bignum's value equals value(bigits_) * 2^(exponent_ * kBigitSize).
  int exponent_;

  DISALLOW_COPY_AND_ASSIGN(Bignum);
};

}  // namespace double_conversion

#endif  // DOUBLE_CONVERSION_BIGNUM_H_
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