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1 // Copyright 2010 the V8 project authors. All rights reserved.
2 // Redistribution and use in source and binary forms, with or without
3 // modification, are permitted provided that the following conditions are
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5 //
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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);
Times10()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);
Equal(const Bignum & a,const Bignum & b)75         static bool Equal(const Bignum& a, const Bignum& b) {
76             return Compare(a, b) == 0;
77         }
LessEqual(const Bignum & a,const Bignum & b)78         static bool LessEqual(const Bignum& a, const Bignum& b) {
79             return Compare(a, b) <= 0;
80         }
Less(const Bignum & a,const Bignum & b)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
PlusEqual(const Bignum & a,const Bignum & b,const Bignum & 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
PlusLessEqual(const Bignum & a,const Bignum & b,const Bignum & 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
PlusLess(const Bignum & a,const Bignum & b,const Bignum & 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 
EnsureCapacity(int size)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.
BigitLength()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_
146