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// Copyright 2010 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_NUMBERS_BIGNUM_H_
#define V8_NUMBERS_BIGNUM_H_
#include "src/utils/vector.h"
namespace v8 {
namespace internal {
class V8_EXPORT_PRIVATE Bignum {
public:
// 3584 = 128 * 28. We can represent 2^3584 > 10^1000 accurately.
// This bignum can encode much bigger numbers, since it contains an
// exponent.
static const int kMaxSignificantBits = 3584;
Bignum();
void AssignUInt16(uint16_t value);
void AssignUInt64(uint64_t value);
void AssignBignum(const Bignum& other);
void AssignDecimalString(Vector<const char> value);
void AssignHexString(Vector<const char> value);
void AssignPowerUInt16(uint16_t base, int exponent);
void AddUInt16(uint16_t operand);
void AddUInt64(uint64_t operand);
void AddBignum(const Bignum& other);
// Precondition: this >= other.
void SubtractBignum(const Bignum& other);
void Square();
void ShiftLeft(int shift_amount);
void MultiplyByUInt32(uint32_t factor);
void MultiplyByUInt64(uint64_t factor);
void MultiplyByPowerOfTen(int exponent);
void Times10() { return MultiplyByUInt32(10); }
// Pseudocode:
// int result = this / other;
// this = this % other;
// In the worst case this function is in O(this/other).
uint16_t DivideModuloIntBignum(const Bignum& other);
bool ToHexString(char* buffer, int buffer_size) const;
static int Compare(const Bignum& a, const Bignum& b);
static bool Equal(const Bignum& a, const Bignum& b) {
return Compare(a, b) == 0;
}
static bool LessEqual(const Bignum& a, const Bignum& b) {
return Compare(a, b) <= 0;
}
static bool Less(const Bignum& a, const Bignum& b) {
return Compare(a, b) < 0;
}
// Returns Compare(a + b, c);
static int PlusCompare(const Bignum& a, const Bignum& b, const Bignum& c);
// Returns a + b == c
static bool PlusEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
return PlusCompare(a, b, c) == 0;
}
// Returns a + b <= c
static bool PlusLessEqual(const Bignum& a, const Bignum& b, const Bignum& c) {
return PlusCompare(a, b, c) <= 0;
}
// Returns a + b < c
static bool PlusLess(const Bignum& a, const Bignum& b, const Bignum& c) {
return PlusCompare(a, b, c) < 0;
}
private:
typedef uint32_t Chunk;
typedef uint64_t DoubleChunk;
static const int kChunkSize = sizeof(Chunk) * 8;
static const int kDoubleChunkSize = sizeof(DoubleChunk) * 8;
// With bigit size of 28 we loose some bits, but a double still fits easily
// into two chunks, and more importantly we can use the Comba multiplication.
static const int kBigitSize = 28;
static const Chunk kBigitMask = (1 << kBigitSize) - 1;
// Every instance allocates kBigitLength chunks on the stack. Bignums cannot
// grow. There are no checks if the stack-allocated space is sufficient.
static const int kBigitCapacity = kMaxSignificantBits / kBigitSize;
void EnsureCapacity(int size) {
if (size > kBigitCapacity) {
UNREACHABLE();
}
}
void Align(const Bignum& other);
void Clamp();
bool IsClamped() const;
void Zero();
// Requires this to have enough capacity (no tests done).
// Updates used_digits_ if necessary.
// by must be < kBigitSize.
void BigitsShiftLeft(int shift_amount);
// BigitLength includes the "hidden" digits encoded in the exponent.
int BigitLength() const { return used_digits_ + exponent_; }
Chunk BigitAt(int index) const;
void SubtractTimes(const Bignum& other, int factor);
Chunk bigits_buffer_[kBigitCapacity];
// A vector backed by bigits_buffer_. This way accesses to the array are
// checked for out-of-bounds errors.
Vector<Chunk> bigits_;
int used_digits_;
// The Bignum's value equals value(bigits_) * 2^(exponent_ * kBigitSize).
int exponent_;
DISALLOW_COPY_AND_ASSIGN(Bignum);
};
} // namespace internal
} // namespace v8
#endif // V8_NUMBERS_BIGNUM_H_