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); Times10()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); Equal(const Bignum & a,const Bignum & b)72 static bool Equal(const Bignum& a, const Bignum& b) { 73 return Compare(a, b) == 0; 74 } LessEqual(const Bignum & a,const Bignum & b)75 static bool LessEqual(const Bignum& a, const Bignum& b) { 76 return Compare(a, b) <= 0; 77 } Less(const Bignum & a,const Bignum & b)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 PlusEqual(const Bignum & a,const Bignum & b,const Bignum & 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 PlusLessEqual(const Bignum & a,const Bignum & b,const Bignum & 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 PlusLess(const Bignum & a,const Bignum & b,const Bignum & c)92 static bool PlusLess(const Bignum& a, const Bignum& b, const Bignum& c) { 93 return PlusCompare(a, b, c) < 0; 94 } 95 96 private: 97 typedef uint32_t Chunk; 98 typedef uint64_t DoubleChunk; 99 100 static const int kChunkSize = sizeof(Chunk) * 8; 101 static const int kDoubleChunkSize = sizeof(DoubleChunk) * 8; 102 // With bigit size of 28 we loose some bits, but a double still fits easily 103 // into two chunks, and more importantly we can use the Comba multiplication. 104 static const int kBigitSize = 28; 105 static const Chunk kBigitMask = (1 << kBigitSize) - 1; 106 // Every instance allocates kBigitLength chunks on the stack. Bignums cannot 107 // grow. There are no checks if the stack-allocated space is sufficient. 108 static const int kBigitCapacity = kMaxSignificantBits / kBigitSize; 109 EnsureCapacity(int size)110 void EnsureCapacity(int size) { 111 if (size > kBigitCapacity) { 112 UNREACHABLE(); 113 } 114 } 115 void Align(const Bignum& other); 116 void Clamp(); 117 bool IsClamped() const; 118 void Zero(); 119 // Requires this to have enough capacity (no tests done). 120 // Updates used_digits_ if necessary. 121 // by must be < kBigitSize. 122 void BigitsShiftLeft(int shift_amount); 123 // BigitLength includes the "hidden" digits encoded in the exponent. BigitLength()124 int BigitLength() const { return used_digits_ + exponent_; } 125 Chunk BigitAt(int index) const; 126 void SubtractTimes(const Bignum& other, int factor); 127 128 Chunk bigits_buffer_[kBigitCapacity]; 129 // A vector backed by bigits_buffer_. This way accesses to the array are 130 // checked for out-of-bounds errors. 131 Vector<Chunk> bigits_; 132 int used_digits_; 133 // The Bignum's value equals value(bigits_) * 2^(exponent_ * kBigitSize). 134 int exponent_; 135 136 DISALLOW_COPY_AND_ASSIGN(Bignum); 137 }; 138 139 } } // namespace v8::internal 140 141 #endif // V8_BIGNUM_H_ 142