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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() : used_bigits_(0), exponent_(0) {}
 
   void AssignUInt16(const uint16_t value);
   void AssignUInt64(uint64_t value);
   void AssignBignum(const Bignum& other);
 
   void AssignDecimalString(const Vector<const char> value);
   void AssignHexString(const Vector<const char> value);
 
   void AssignPowerUInt16(uint16_t base, const int exponent);
 
   void AddUInt64(const uint64_t operand);
   void AddBignum(const Bignum& other);
   // Precondition: this >= other.
   void SubtractBignum(const Bignum& other);
 
   void Square();
   void ShiftLeft(const int shift_amount);
   void MultiplyByUInt32(const uint32_t factor);
   void MultiplyByUInt64(const uint64_t factor);
   void MultiplyByPowerOfTen(const 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, const 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;
 
   static void EnsureCapacity(const int size) {
     if (size > kBigitCapacity) {
       DOUBLE_CONVERSION_UNREACHABLE();
     }
   }
   void Align(const Bignum& other);
   void Clamp();
   bool IsClamped() const {
     return used_bigits_ == 0 || RawBigit(used_bigits_ - 1) != 0;
   }
   void Zero() {
     used_bigits_ = 0;
     exponent_ = 0;
   }
   // Requires this to have enough capacity (no tests done).
   // Updates used_bigits_ if necessary.
   // shift_amount must be < kBigitSize.
   void BigitsShiftLeft(const int shift_amount);
   // BigitLength includes the "hidden" bigits encoded in the exponent.
   int BigitLength() const { return used_bigits_ + exponent_; }
   Chunk& RawBigit(const int index);
   const Chunk& RawBigit(const int index) const;
   Chunk BigitOrZero(const int index) const;
   void SubtractTimes(const Bignum& other, const int factor);
 
   // The Bignum's value is value(bigits_buffer_) * 2^(exponent_ * kBigitSize),
   // where the value of the buffer consists of the lower kBigitSize bits of
   // the first used_bigits_ Chunks in bigits_buffer_, first chunk has lowest
   // significant bits.
   int16_t used_bigits_;
   int16_t exponent_;
   Chunk bigits_buffer_[kBigitCapacity];
 
   DOUBLE_CONVERSION_DISALLOW_COPY_AND_ASSIGN(Bignum);
 };
 
 }  // namespace double_conversion
 
 #endif  // DOUBLE_CONVERSION_BIGNUM_H_

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