Russell Brenner | 90bac25 | 2010-11-18 13:33:46 -0800 | [diff] [blame^] | 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 |
| 4 | // met: |
| 5 | // |
| 6 | // * Redistributions of source code must retain the above copyright |
| 7 | // notice, this list of conditions and the following disclaimer. |
| 8 | // * Redistributions in binary form must reproduce the above |
| 9 | // copyright notice, this list of conditions and the following |
| 10 | // disclaimer in the documentation and/or other materials provided |
| 11 | // with the distribution. |
| 12 | // * Neither the name of Google Inc. nor the names of its |
| 13 | // contributors may be used to endorse or promote products derived |
| 14 | // from this software without specific prior written permission. |
| 15 | // |
| 16 | // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 17 | // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 18 | // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| 19 | // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| 20 | // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| 21 | // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| 22 | // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 23 | // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 24 | // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 25 | // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| 26 | // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| 27 | |
| 28 | #ifndef V8_BIGNUM_H_ |
| 29 | #define V8_BIGNUM_H_ |
| 30 | |
| 31 | namespace v8 { |
| 32 | namespace internal { |
| 33 | |
| 34 | class Bignum { |
| 35 | public: |
| 36 | // 3584 = 128 * 28. We can represent 2^3584 > 10^1000 accurately. |
| 37 | // This bignum can encode much bigger numbers, since it contains an |
| 38 | // exponent. |
| 39 | static const int kMaxSignificantBits = 3584; |
| 40 | |
| 41 | Bignum(); |
| 42 | void AssignUInt16(uint16_t value); |
| 43 | void AssignUInt64(uint64_t value); |
| 44 | void AssignBignum(const Bignum& other); |
| 45 | |
| 46 | void AssignDecimalString(Vector<const char> value); |
| 47 | void AssignHexString(Vector<const char> value); |
| 48 | |
| 49 | void AssignPowerUInt16(uint16_t base, int exponent); |
| 50 | |
| 51 | void AddUInt16(uint16_t operand); |
| 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(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 | static int Compare(const Bignum& a, const Bignum& b); |
| 72 | static bool Equal(const Bignum& a, const Bignum& b) { |
| 73 | return Compare(a, b) == 0; |
| 74 | } |
| 75 | static bool LessEqual(const Bignum& a, const Bignum& b) { |
| 76 | return Compare(a, b) <= 0; |
| 77 | } |
| 78 | static bool Less(const Bignum& a, const Bignum& b) { |
| 79 | return Compare(a, b) < 0; |
| 80 | } |
| 81 | // Returns Compare(a + b, c); |
| 82 | static int PlusCompare(const Bignum& a, const Bignum& b, const Bignum& c); |
| 83 | // Returns a + b == c |
| 84 | static bool PlusEqual(const Bignum& a, const Bignum& b, const Bignum& c) { |
| 85 | return PlusCompare(a, b, c) == 0; |
| 86 | } |
| 87 | // Returns a + b <= c |
| 88 | static bool PlusLessEqual(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 PlusLess(const Bignum& a, const Bignum& b, const Bignum& c) { |
| 93 | return PlusCompare(a, b, c) < 0; |
| 94 | } |
| 95 | private: |
| 96 | typedef uint32_t Chunk; |
| 97 | typedef uint64_t DoubleChunk; |
| 98 | |
| 99 | static const int kChunkSize = sizeof(Chunk) * 8; |
| 100 | static const int kDoubleChunkSize = sizeof(DoubleChunk) * 8; |
| 101 | // With bigit size of 28 we loose some bits, but a double still fits easily |
| 102 | // into two chunks, and more importantly we can use the Comba multiplication. |
| 103 | static const int kBigitSize = 28; |
| 104 | static const Chunk kBigitMask = (1 << kBigitSize) - 1; |
| 105 | // Every instance allocates kBigitLength chunks on the stack. Bignums cannot |
| 106 | // grow. There are no checks if the stack-allocated space is sufficient. |
| 107 | static const int kBigitCapacity = kMaxSignificantBits / kBigitSize; |
| 108 | |
| 109 | void EnsureCapacity(int size) { |
| 110 | if (size > kBigitCapacity) { |
| 111 | UNREACHABLE(); |
| 112 | } |
| 113 | } |
| 114 | void Align(const Bignum& other); |
| 115 | void Clamp(); |
| 116 | bool IsClamped() const; |
| 117 | void Zero(); |
| 118 | // Requires this to have enough capacity (no tests done). |
| 119 | // Updates used_digits_ if necessary. |
| 120 | // by must be < kBigitSize. |
| 121 | void BigitsShiftLeft(int shift_amount); |
| 122 | // BigitLength includes the "hidden" digits encoded in the exponent. |
| 123 | int BigitLength() const { return used_digits_ + exponent_; } |
| 124 | Chunk BigitAt(int index) const; |
| 125 | void SubtractTimes(const Bignum& other, int factor); |
| 126 | |
| 127 | Chunk bigits_buffer_[kBigitCapacity]; |
| 128 | // A vector backed by bigits_buffer_. This way accesses to the array are |
| 129 | // checked for out-of-bounds errors. |
| 130 | Vector<Chunk> bigits_; |
| 131 | int used_digits_; |
| 132 | // The Bignum's value equals value(bigits_) * 2^(exponent_ * kBigitSize). |
| 133 | int exponent_; |
| 134 | |
| 135 | DISALLOW_COPY_AND_ASSIGN(Bignum); |
| 136 | }; |
| 137 | |
| 138 | } } // namespace v8::internal |
| 139 | |
| 140 | #endif // V8_BIGNUM_H_ |