1// Copyright 2010 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef V8_BIGNUM_H_
6#define V8_BIGNUM_H_
7
8#include "src/vector.h"
9
10namespace v8 {
11namespace internal {
12
13class V8_EXPORT_PRIVATE Bignum {
14 public:
15 // 3584 = 128 * 28. We can represent 2^3584 > 10^1000 accurately.
16 // This bignum can encode much bigger numbers, since it contains an
17 // exponent.
18 static const int kMaxSignificantBits = 3584;
19
20 Bignum();
21 void AssignUInt16(uint16_t value);
22 void AssignUInt64(uint64_t value);
23 void AssignBignum(const Bignum& other);
24
25 void AssignDecimalString(Vector<const char> value);
26 void AssignHexString(Vector<const char> value);
27
28 void AssignPowerUInt16(uint16_t base, int exponent);
29
30 void AddUInt16(uint16_t operand);
31 void AddUInt64(uint64_t operand);
32 void AddBignum(const Bignum& other);
33 // Precondition: this >= other.
34 void SubtractBignum(const Bignum& other);
35
36 void Square();
37 void ShiftLeft(int shift_amount);
38 void MultiplyByUInt32(uint32_t factor);
39 void MultiplyByUInt64(uint64_t factor);
40 void MultiplyByPowerOfTen(int exponent);
41 void Times10() { return MultiplyByUInt32(10); }
42 // Pseudocode:
43 // int result = this / other;
44 // this = this % other;
45 // In the worst case this function is in O(this/other).
46 uint16_t DivideModuloIntBignum(const Bignum& other);
47
48 bool ToHexString(char* buffer, int buffer_size) const;
49
50 static int Compare(const Bignum& a, const Bignum& b);
51 static bool Equal(const Bignum& a, const Bignum& b) {
52 return Compare(a, b) == 0;
53 }
54 static bool LessEqual(const Bignum& a, const Bignum& b) {
55 return Compare(a, b) <= 0;
56 }
57 static bool Less(const Bignum& a, const Bignum& b) {
58 return Compare(a, b) < 0;
59 }
60 // Returns Compare(a + b, c);
61 static int PlusCompare(const Bignum& a, const Bignum& b, const Bignum& c);
62 // Returns a + b == c
63 static bool PlusEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
64 return PlusCompare(a, b, c) == 0;
65 }
66 // Returns a + b <= c
67 static bool PlusLessEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
68 return PlusCompare(a, b, c) <= 0;
69 }
70 // Returns a + b < c
71 static bool PlusLess(const Bignum& a, const Bignum& b, const Bignum& c) {
72 return PlusCompare(a, b, c) < 0;
73 }
74
75 private:
76 typedef uint32_t Chunk;
77 typedef uint64_t DoubleChunk;
78
79 static const int kChunkSize = sizeof(Chunk) * 8;
80 static const int kDoubleChunkSize = sizeof(DoubleChunk) * 8;
81 // With bigit size of 28 we loose some bits, but a double still fits easily
82 // into two chunks, and more importantly we can use the Comba multiplication.
83 static const int kBigitSize = 28;
84 static const Chunk kBigitMask = (1 << kBigitSize) - 1;
85 // Every instance allocates kBigitLength chunks on the stack. Bignums cannot
86 // grow. There are no checks if the stack-allocated space is sufficient.
87 static const int kBigitCapacity = kMaxSignificantBits / kBigitSize;
88
89 void EnsureCapacity(int size) {
90 if (size > kBigitCapacity) {
91 UNREACHABLE();
92 }
93 }
94 void Align(const Bignum& other);
95 void Clamp();
96 bool IsClamped() const;
97 void Zero();
98 // Requires this to have enough capacity (no tests done).
99 // Updates used_digits_ if necessary.
100 // by must be < kBigitSize.
101 void BigitsShiftLeft(int shift_amount);
102 // BigitLength includes the "hidden" digits encoded in the exponent.
103 int BigitLength() const { return used_digits_ + exponent_; }
104 Chunk BigitAt(int index) const;
105 void SubtractTimes(const Bignum& other, int factor);
106
107 Chunk bigits_buffer_[kBigitCapacity];
108 // A vector backed by bigits_buffer_. This way accesses to the array are
109 // checked for out-of-bounds errors.
110 Vector<Chunk> bigits_;
111 int used_digits_;
112 // The Bignum's value equals value(bigits_) * 2^(exponent_ * kBigitSize).
113 int exponent_;
114
115 DISALLOW_COPY_AND_ASSIGN(Bignum);
116};
117
118} // namespace internal
119} // namespace v8
120
121#endif // V8_BIGNUM_H_
122