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 #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_