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27
28#ifndef DOUBLE_CONVERSION_BIGNUM_H_
29#define DOUBLE_CONVERSION_BIGNUM_H_
30
31#include <double-conversion/utils.h>
32
33namespace double_conversion {
34
35class 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(factor: 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_
145

source code of qtbase/src/3rdparty/double-conversion/bignum.h