Bitcoin Core  27.99.0
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arith_uint256 Class Reference

256-bit unsigned big integer. More...

#include <arith_uint256.h>

Inheritance diagram for arith_uint256:
Collaboration diagram for arith_uint256:

Public Member Functions

 arith_uint256 ()
 arith_uint256 (const base_uint< 256 > &b)
 arith_uint256 (uint64_t b)
arith_uint256SetCompact (uint32_t nCompact, bool *pfNegative=nullptr, bool *pfOverflow=nullptr)
 The "compact" format is a representation of a whole number N using an unsigned 32bit number similar to a floating point format. More...
uint32_t GetCompact (bool fNegative=false) const
- Public Member Functions inherited from base_uint< 256 >
 base_uint ()
 base_uint (const base_uint &b)
 base_uint (uint64_t b)
base_uintoperator= (const base_uint &b)
base_uintoperator= (uint64_t b)
base_uint operator~ () const
base_uint operator- () const
double getdouble () const
base_uintoperator^= (const base_uint &b)
base_uintoperator^= (uint64_t b)
base_uintoperator&= (const base_uint &b)
base_uintoperator|= (const base_uint &b)
base_uintoperator|= (uint64_t b)
base_uintoperator<<= (unsigned int shift)
base_uintoperator>>= (unsigned int shift)
base_uintoperator+= (const base_uint &b)
base_uintoperator+= (uint64_t b64)
base_uintoperator-= (const base_uint &b)
base_uintoperator-= (uint64_t b64)
base_uintoperator*= (uint32_t b32)
base_uintoperator*= (const base_uint &b)
base_uintoperator/= (const base_uint &b)
base_uintoperator++ ()
base_uint operator++ (int)
base_uintoperator-- ()
base_uint operator-- (int)
int CompareTo (const base_uint &b) const
bool EqualTo (uint64_t b) const
std::string GetHex () const
std::string ToString () const
unsigned int size () const
unsigned int bits () const
 Returns the position of the highest bit set plus one, or zero if the value is zero. More...
uint64_t GetLow64 () const


uint256 ArithToUint256 (const arith_uint256 &)
arith_uint256 UintToArith256 (const uint256 &)

Additional Inherited Members

- Protected Attributes inherited from base_uint< 256 >
uint32_t pn [WIDTH]
- Static Protected Attributes inherited from base_uint< 256 >
static constexpr int WIDTH

Detailed Description

256-bit unsigned big integer.

Definition at line 241 of file arith_uint256.h.

Constructor & Destructor Documentation

◆ arith_uint256() [1/3]

arith_uint256::arith_uint256 ( )

Definition at line 243 of file arith_uint256.h.

◆ arith_uint256() [2/3]

arith_uint256::arith_uint256 ( const base_uint< 256 > &  b)

Definition at line 244 of file arith_uint256.h.

◆ arith_uint256() [3/3]

arith_uint256::arith_uint256 ( uint64_t  b)

Definition at line 245 of file arith_uint256.h.

Member Function Documentation

◆ GetCompact()

uint32_t arith_uint256::GetCompact ( bool  fNegative = false) const

Definition at line 195 of file arith_uint256.cpp.

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◆ SetCompact()

arith_uint256 & arith_uint256::SetCompact ( uint32_t  nCompact,
bool *  pfNegative = nullptr,
bool *  pfOverflow = nullptr 

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.

Definition at line 175 of file arith_uint256.cpp.

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Friends And Related Function Documentation

◆ ArithToUint256

uint256 ArithToUint256 ( const arith_uint256 )

Definition at line 218 of file arith_uint256.cpp.

◆ UintToArith256

arith_uint256 UintToArith256 ( const uint256 )

Definition at line 225 of file arith_uint256.cpp.

The documentation for this class was generated from the following files: