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 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); 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); 75 static bool Equal(const Bignum& a, const Bignum& b) { 76 return Compare(a, b) == 0; 77 } 78 static bool LessEqual(const Bignum& a, const Bignum& b) { 79 return Compare(a, b) <= 0; 80 } 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 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 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 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; 111 112 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. 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
