ceph/src/arrow/cpp/src/arrow/vendored/double-conversion/bignum.h

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  27
  28 #ifndef DOUBLE_CONVERSION_BIGNUM_H_
  29 #define DOUBLE_CONVERSION_BIGNUM_H_
  30
  31 #include "utils.h"
  32
  33 namespace double_conversion {
  34
  35 class Bignum {
  36  public:
  37   // 3584 = 128 * 28. We can represent 2^3584 > 10^1000 accurately.
  38   // This bignum can encode much bigger numbers, since it contains an
  39   // exponent.
  40   static const int kMaxSignificantBits = 3584;
  41
  42   Bignum();
  43   void AssignUInt16(uint16_t value);
  44   void AssignUInt64(uint64_t value);
  45   void AssignBignum(const Bignum& other);
  46
  47   void AssignDecimalString(Vector<const char> value);
  48   void AssignHexString(Vector<const char> value);
  49
  50   void AssignPowerUInt16(uint16_t base, int exponent);
  51
  52   void AddUInt64(uint64_t operand);
  53   void AddBignum(const Bignum& other);
  54   // Precondition: this >= other.
  55   void SubtractBignum(const Bignum& other);
  56
  57   void Square();
  58   void ShiftLeft(int shift_amount);
  59   void MultiplyByUInt32(uint32_t factor);
  60   void MultiplyByUInt64(uint64_t factor);
  61   void MultiplyByPowerOfTen(int exponent);
  62   void Times10() { return MultiplyByUInt32(10); }
  63   // Pseudocode:
  64   //  int result = this / other;
  65   //  this = this % other;
  66   // In the worst case this function is in O(this/other).
  67   uint16_t DivideModuloIntBignum(const Bignum& other);
  68
  69   bool ToHexString(char* buffer, int buffer_size) const;
  70
  71   // Returns
  72   //  -1 if a < b,
  73   //   0 if a == b, and
  74   //  +1 if a > b.
  75   static int Compare(const Bignum& a, const Bignum& b);
  76   static bool Equal(const Bignum& a, const Bignum& b) {
  77     return Compare(a, b) == 0;
  78   }
  79   static bool LessEqual(const Bignum& a, const Bignum& b) {
  80     return Compare(a, b) <= 0;
  81   }
  82   static bool Less(const Bignum& a, const Bignum& b) {
  83     return Compare(a, b) < 0;
  84   }
  85   // Returns Compare(a + b, c);
  86   static int PlusCompare(const Bignum& a, const Bignum& b, const Bignum& c);
  87   // Returns a + b == c
  88   static bool PlusEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
  89     return PlusCompare(a, b, c) == 0;
  90   }
  91   // Returns a + b <= c
  92   static bool PlusLessEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
  93     return PlusCompare(a, b, c) <= 0;
  94   }
  95   // Returns a + b < c
  96   static bool PlusLess(const Bignum& a, const Bignum& b, const Bignum& c) {
  97     return PlusCompare(a, b, c) < 0;
  98   }
  99  private:
 100   typedef uint32_t Chunk;
 101   typedef uint64_t DoubleChunk;
 102
 103   static const int kChunkSize = sizeof(Chunk) * 8;
 104   static const int kDoubleChunkSize = sizeof(DoubleChunk) * 8;
 105   // With bigit size of 28 we loose some bits, but a double still fits easily
 106   // into two chunks, and more importantly we can use the Comba multiplication.
 107   static const int kBigitSize = 28;
 108   static const Chunk kBigitMask = (1 << kBigitSize) - 1;
 109   // Every instance allocates kBigitLength chunks on the stack. Bignums cannot
 110   // grow. There are no checks if the stack-allocated space is sufficient.
 111   static const int kBigitCapacity = kMaxSignificantBits / kBigitSize;
 112
 113   void EnsureCapacity(int size) {
 114     if (size > kBigitCapacity) {
 115       UNREACHABLE();
 116     }
 117   }
 118   void Align(const Bignum& other);
 119   void Clamp();
 120   bool IsClamped() const;
 121   void Zero();
 122   // Requires this to have enough capacity (no tests done).
 123   // Updates used_digits_ if necessary.
 124   // shift_amount must be < kBigitSize.
 125   void BigitsShiftLeft(int shift_amount);
 126   // BigitLength includes the "hidden" digits encoded in the exponent.
 127   int BigitLength() const { return used_digits_ + exponent_; }
 128   Chunk BigitAt(int index) const;
 129   void SubtractTimes(const Bignum& other, int factor);
 130
 131   Chunk bigits_buffer_[kBigitCapacity];
 132   // A vector backed by bigits_buffer_. This way accesses to the array are
 133   // checked for out-of-bounds errors.
 134   Vector<Chunk> bigits_;
 135   int used_digits_;
 136   // The Bignum's value equals value(bigits_) * 2^(exponent_ * kBigitSize).
 137   int exponent_;
 138
 139   DC_DISALLOW_COPY_AND_ASSIGN(Bignum);
 140 };
 141
 142 }  // namespace double_conversion
 143
 144 #endif  // DOUBLE_CONVERSION_BIGNUM_H_