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27
28#ifndef DOUBLE_CONVERSION_BIGNUM_H_
29#define DOUBLE_CONVERSION_BIGNUM_H_
30
31#include <wtf/dtoa/utils.h>
32
33namespace WTF {
34namespace double_conversion {
35
36class Bignum {
37 public:
38 // 3584 = 128 * 28. We can represent 2^3584 > 10^1000 accurately.
39 // This bignum can encode much bigger numbers, since it contains an
40 // exponent.
41 static const int kMaxSignificantBits = 3584;
42
43 Bignum();
44 void AssignUInt16(uint16_t value);
45 void AssignUInt64(uint64_t value);
46 void AssignBignum(const Bignum& other);
47
48 void AssignDecimalString(BufferReference<const char> value);
49 void AssignHexString(BufferReference<const char> value);
50
51 void AssignPowerUInt16(uint16_t base, int exponent);
52
53 void AddUInt64(uint64_t operand);
54 void AddBignum(const Bignum& other);
55 // Precondition: this >= other.
56 void SubtractBignum(const Bignum& other);
57
58 void Square();
59 void ShiftLeft(int shift_amount);
60 void MultiplyByUInt32(uint32_t factor);
61 void MultiplyByUInt64(uint64_t factor);
62 void MultiplyByPowerOfTen(int exponent);
63 void Times10() { return MultiplyByUInt32(10); }
64 // Pseudocode:
65 // int result = this / other;
66 // this = this % other;
67 // In the worst case this function is in O(this/other).
68 uint16_t DivideModuloIntBignum(const Bignum& other);
69
70 bool ToHexString(char* buffer, int buffer_size) const;
71
72 // Returns
73 // -1 if a < b,
74 // 0 if a == b, and
75 // +1 if a > b.
76 static int Compare(const Bignum& a, const Bignum& b);
77 static bool Equal(const Bignum& a, const Bignum& b) {
78 return Compare(a, b) == 0;
79 }
80 static bool LessEqual(const Bignum& a, const Bignum& b) {
81 return Compare(a, b) <= 0;
82 }
83 static bool Less(const Bignum& a, const Bignum& b) {
84 return Compare(a, b) < 0;
85 }
86 // Returns Compare(a + b, c);
87 static int PlusCompare(const Bignum& a, const Bignum& b, const Bignum& c);
88 // Returns a + b == c
89 static bool PlusEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
90 return PlusCompare(a, b, c) == 0;
91 }
92 // Returns a + b <= c
93 static bool PlusLessEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
94 return PlusCompare(a, b, c) <= 0;
95 }
96 // Returns a + b < c
97 static bool PlusLess(const Bignum& a, const Bignum& b, const Bignum& c) {
98 return PlusCompare(a, b, c) < 0;
99 }
100 private:
101 typedef uint32_t Chunk;
102 typedef uint64_t DoubleChunk;
103
104 static const int kChunkSize = sizeof(Chunk) * 8;
105 static const int kDoubleChunkSize = sizeof(DoubleChunk) * 8;
106 // With bigit size of 28 we loose some bits, but a double still fits easily
107 // into two chunks, and more importantly we can use the Comba multiplication.
108 static const int kBigitSize = 28;
109 static const Chunk kBigitMask = (1 << kBigitSize) - 1;
110 // Every instance allocates kBigitLength chunks on the stack. Bignums cannot
111 // grow. There are no checks if the stack-allocated space is sufficient.
112 static const int kBigitCapacity = kMaxSignificantBits / kBigitSize;
113
114 void EnsureCapacity(int size) {
115 if (size > kBigitCapacity) {
116 UNREACHABLE();
117 }
118 }
119 void Align(const Bignum& other);
120 void Clamp();
121 bool IsClamped() const;
122 void Zero();
123 // Requires this to have enough capacity (no tests done).
124 // Updates used_digits_ if necessary.
125 // shift_amount must be < kBigitSize.
126 void BigitsShiftLeft(int shift_amount);
127 // BigitLength includes the "hidden" digits encoded in the exponent.
128 int BigitLength() const { return used_digits_ + exponent_; }
129 Chunk BigitAt(int index) const;
130 void SubtractTimes(const Bignum& other, int factor);
131
132 Chunk bigits_buffer_[kBigitCapacity];
133 // A BufferReference backed by bigits_buffer_. This way accesses to the array are
134 // checked for out-of-bounds errors.
135 BufferReference<Chunk> bigits_;
136 int used_digits_;
137 // The Bignum's value equals value(bigits_) * 2^(exponent_ * kBigitSize).
138 int exponent_;
139
140 DC_DISALLOW_COPY_AND_ASSIGN(Bignum);
141};
142
143} // namespace double_conversion
144} // namespace WTF
145
146#endif // DOUBLE_CONVERSION_BIGNUM_H_
147