Bitcoin

src/arith_uint256.h

// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-present The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_ARITH_UINT256_H
#define BITCOIN_ARITH_UINT256_H
#include <compare>
#include <cstdint>
#include <cstring>
#include <limits>
#include <stdexcept>
#include <string>
class uint256;
class uint_error : public std::runtime_error {
public:
explicit uint_error(const std::string& str) : std::runtime_error(str) {}
};
/** Template base class for unsigned big integers. */
template <unsigned int BITS>
class base_uint
{
protected:
static_assert(BITS / 32 > 0 && BITS % 32 == 0, "Template parameter BITS must be a positive multiple of 32.");
static constexpr int WIDTH = BITS / 32;
/** Big integer represented with 32-bit digits, least-significant first. */
uint32_t pn[WIDTH];
public:
constexpr base_uint()
{
for (int i = 0; i < WIDTH; i++)
pn[i] = 0;
}
base_uint(const base_uint& b) = default;
base_uint& operator=(const base_uint& b) = default;
constexpr base_uint(uint64_t b)
{
pn[0] = (unsigned int)b;
pn[1] = (unsigned int)(b >> 32);
for (int i = 2; i < WIDTH; i++)
pn[i] = 0;
}
base_uint operator~() const
{
base_uint ret;
for (int i = 0; i < WIDTH; i++)
ret.pn[i] = ~pn[i];
return ret;
}
base_uint operator-() const
{
base_uint ret;
for (int i = 0; i < WIDTH; i++)
ret.pn[i] = ~pn[i];
++ret;
return ret;
}
double getdouble() const;
base_uint& operator=(uint64_t b)
{
pn[0] = (unsigned int)b;
pn[1] = (unsigned int)(b >> 32);
for (int i = 2; i < WIDTH; i++)
pn[i] = 0;
return *this;
}
base_uint& operator^=(const base_uint& b)
{
for (int i = 0; i < WIDTH; i++)
pn[i] ^= b.pn[i];
return *this;
}
base_uint& operator&=(const base_uint& b)
{
for (int i = 0; i < WIDTH; i++)
pn[i] &= b.pn[i];
return *this;
}
base_uint& operator|=(const base_uint& b)
{
for (int i = 0; i < WIDTH; i++)
pn[i] |= b.pn[i];
return *this;
}
base_uint& operator^=(uint64_t b)
{
pn[0] ^= (unsigned int)b;
pn[1] ^= (unsigned int)(b >> 32);
return *this;
}
base_uint& operator|=(uint64_t b)
{
pn[0] |= (unsigned int)b;
pn[1] |= (unsigned int)(b >> 32);
return *this;
}
base_uint& operator<<=(unsigned int shift);
base_uint& operator>>=(unsigned int shift);
base_uint& operator+=(const base_uint& b)
{
uint64_t carry = 0;
for (int i = 0; i < WIDTH; i++)
{
uint64_t n = carry + pn[i] + b.pn[i];
pn[i] = n & 0xffffffff;
carry = n >> 32;
}
return *this;
}
base_uint& operator-=(const base_uint& b)
{
*this += -b;
return *this;
}
base_uint& operator+=(uint64_t b64)
{
base_uint b;
b = b64;
*this += b;
return *this;
}
base_uint& operator-=(uint64_t b64)
{
base_uint b;
b = b64;
*this += -b;
return *this;
}
base_uint& operator*=(uint32_t b32);
base_uint& operator*=(const base_uint& b);
base_uint& operator/=(const base_uint& b);
base_uint& operator++()
{
// prefix operator
int i = 0;
while (i < WIDTH && ++pn[i] == 0)
i++;
return *this;
}
base_uint operator++(int)
{
// postfix operator
const base_uint ret = *this;
++(*this);
return ret;
}
base_uint& operator--()
{
// prefix operator
int i = 0;
while (i < WIDTH && --pn[i] == std::numeric_limits<uint32_t>::max())
i++;
return *this;
}
base_uint operator--(int)
{
// postfix operator
const base_uint ret = *this;
--(*this);
return ret;
}
/** Numeric ordering (unlike \ref base_blob::Compare) */
int CompareTo(const base_uint& b) const;
bool EqualTo(uint64_t b) const;
friend inline base_uint operator+(const base_uint& a, const base_uint& b) { return base_uint(a) += b; }
friend inline base_uint operator-(const base_uint& a, const base_uint& b) { return base_uint(a) -= b; }
friend inline base_uint operator*(const base_uint& a, const base_uint& b) { return base_uint(a) *= b; }
friend inline base_uint operator/(const base_uint& a, const base_uint& b) { return base_uint(a) /= b; }
friend inline base_uint operator|(const base_uint& a, const base_uint& b) { return base_uint(a) |= b; }
friend inline base_uint operator&(const base_uint& a, const base_uint& b) { return base_uint(a) &= b; }
friend inline base_uint operator^(const base_uint& a, const base_uint& b) { return base_uint(a) ^= b; }
friend inline base_uint operator>>(const base_uint& a, int shift) { return base_uint(a) >>= shift; }
friend inline base_uint operator<<(const base_uint& a, int shift) { return base_uint(a) <<= shift; }
friend inline base_uint operator*(const base_uint& a, uint32_t b) { return base_uint(a) *= b; }
friend inline bool operator==(const base_uint& a, const base_uint& b) { return memcmp(a.pn, b.pn, sizeof(a.pn)) == 0; }
friend inline std::strong_ordering operator<=>(const base_uint& a, const base_uint& b) { return a.CompareTo(b) <=> 0; }
friend inline bool operator==(const base_uint& a, uint64_t b) { return a.EqualTo(b); }
/** Hex encoding of the number (with the most significant digits first). */
std::string GetHex() const;
std::string ToString() const;
unsigned int size() const
{
return sizeof(pn);
}
/**
* Returns the position of the highest bit set plus one, or zero if the
* value is zero.
*/
unsigned int bits() const;
uint64_t GetLow64() const
{
static_assert(WIDTH >= 2, "Assertion WIDTH >= 2 failed (WIDTH = BITS / 32). BITS is a template parameter.");
return pn[0] | (uint64_t)pn[1] << 32;
}
};
/** 256-bit unsigned big integer. */
class arith_uint256 : public base_uint<256>
{
public:
constexpr arith_uint256() = default;
constexpr arith_uint256(const base_uint& b) : base_uint(b) {}
constexpr arith_uint256(uint64_t b) : base_uint(b) {}
/**
* The "compact" format is a representation of a whole
* number N using an unsigned 32bit number similar to a
* floating point format.
* The most significant 8 bits are the unsigned exponent of base 256.
* This exponent can be thought of as "number of bytes of N".
* The lower 23 bits are the mantissa.
* Bit number 24 (0x800000) represents the sign of N.
* N = (-1^sign) * mantissa * 256^(exponent-3)
*
* Satoshi's original implementation used BN_bn2mpi() and BN_mpi2bn().
* MPI uses the most significant bit of the first byte as sign.
* Thus 0x1234560000 is compact (0x05123456)
* and 0xc0de000000 is compact (0x0600c0de)
*
* Bitcoin only uses this "compact" format for encoding difficulty
* targets, which are unsigned 256bit quantities. Thus, all the
* complexities of the sign bit and using base 256 are probably an
* implementation accident.
*/
arith_uint256& SetCompact(uint32_t nCompact, bool *pfNegative = nullptr, bool *pfOverflow = nullptr);
uint32_t GetCompact(bool fNegative = false) const;
friend uint256 ArithToUint256(const arith_uint256 &);
friend arith_uint256 UintToArith256(const uint256 &);
};
// Keeping the trivially copyable property is beneficial for performance
static_assert(std::is_trivially_copyable_v<arith_uint256>);
uint256 ArithToUint256(const arith_uint256 &);
arith_uint256 UintToArith256(const uint256 &);
extern template class base_uint<256>;
#endif // BITCOIN_ARITH_UINT256_H