third_party/WebKit/Source/wtf/dtoa/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 WTF {
  34
  35 namespace double_conversion {
  36
  37     class Bignum {
  38     public:
  39         // 3584 = 128 * 28. We can represent 2^3584 > 10^1000 accurately.
  40         // This bignum can encode much bigger numbers, since it contains an
  41         // exponent.
  42         static const int kMaxSignificantBits = 3584;
  43
  44         Bignum();
  45         void AssignUInt16(uint16_t value);
  46         void AssignUInt64(uint64_t value);
  47         void AssignBignum(const Bignum& other);
  48
  49         void AssignDecimalString(Vector<const char> value);
  50         void AssignHexString(Vector<const char> value);
  51
  52         void AssignPowerUInt16(uint16_t base, int exponent);
  53
  54         void AddUInt16(uint16_t operand);
  55         void AddUInt64(uint64_t operand);
  56         void AddBignum(const Bignum& other);
  57         // Precondition: this >= other.
  58         void SubtractBignum(const Bignum& other);
  59
  60         void Square();
  61         void ShiftLeft(int shift_amount);
  62         void MultiplyByUInt32(uint32_t factor);
  63         void MultiplyByUInt64(uint64_t factor);
  64         void MultiplyByPowerOfTen(int exponent);
  65         void Times10() { return MultiplyByUInt32(10); }
  66         // Pseudocode:
  67         //  int result = this / other;
  68         //  this = this % other;
  69         // In the worst case this function is in O(this/other).
  70         uint16_t DivideModuloIntBignum(const Bignum& other);
  71
  72         bool ToHexString(char* buffer, int buffer_size) const;
  73
  74         static int Compare(const Bignum& a, const Bignum& b);
  75         static bool Equal(const Bignum& a, const Bignum& b) {
  76             return Compare(a, b) == 0;
  77         }
  78         static bool LessEqual(const Bignum& a, const Bignum& b) {
  79             return Compare(a, b) <= 0;
  80         }
  81         static bool Less(const Bignum& a, const Bignum& b) {
  82             return Compare(a, b) < 0;
  83         }
  84         // Returns Compare(a + b, c);
  85         static int PlusCompare(const Bignum& a, const Bignum& b, const Bignum& c);
  86         // Returns a + b == c
  87         static bool PlusEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
  88             return PlusCompare(a, b, c) == 0;
  89         }
  90         // Returns a + b <= c
  91         static bool PlusLessEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
  92             return PlusCompare(a, b, c) <= 0;
  93         }
  94         // Returns a + b < c
  95         static bool PlusLess(const Bignum& a, const Bignum& b, const Bignum& c) {
  96             return PlusCompare(a, b, c) < 0;
  97         }
  98     private:
  99         typedef uint32_t Chunk;
 100         typedef uint64_t DoubleChunk;
 101
 102         static const int kChunkSize = sizeof(Chunk) * 8;
 103         static const int kDoubleChunkSize = sizeof(DoubleChunk) * 8;
 104         // With bigit size of 28 we loose some bits, but a double still fits easily
 105         // into two chunks, and more importantly we can use the Comba multiplication.
 106         static const int kBigitSize = 28;
 107         static const Chunk kBigitMask = (1 << kBigitSize) - 1;
 108         // Every instance allocates kBigitLength chunks on the stack. Bignums cannot
 109         // grow. There are no checks if the stack-allocated space is sufficient.
 110         static const int kBigitCapacity = kMaxSignificantBits / kBigitSize;
 111
 112         void EnsureCapacity(int size) {
 113             if (size > kBigitCapacity) {
 114                 UNREACHABLE();
 115             }
 116         }
 117         void Align(const Bignum& other);
 118         void Clamp();
 119         bool IsClamped() const;
 120         void Zero();
 121         // Requires this to have enough capacity (no tests done).
 122         // Updates used_digits_ if necessary.
 123         // shift_amount must be < kBigitSize.
 124         void BigitsShiftLeft(int shift_amount);
 125         // BigitLength includes the "hidden" digits encoded in the exponent.
 126         int BigitLength() const { return used_digits_ + exponent_; }
 127         Chunk BigitAt(int index) const;
 128         void SubtractTimes(const Bignum& other, int factor);
 129
 130         Chunk bigits_buffer_[kBigitCapacity];
 131         // A vector backed by bigits_buffer_. This way accesses to the array are
 132         // checked for out-of-bounds errors.
 133         Vector<Chunk> bigits_;
 134         int used_digits_;
 135         // The Bignum's value equals value(bigits_) * 2^(exponent_ * kBigitSize).
 136         int exponent_;
 137
 138         DISALLOW_COPY_AND_ASSIGN(Bignum);
 139     };
 140
 141 }  // namespace double_conversion
 142
 143 } // namespace WTF
 144
 145 #endif  // DOUBLE_CONVERSION_BIGNUM_H_