difficulty

Documentation

Overview

Package difficulty 难度计算基础函数

Index

• func BigToCompact(n *big.Int) uint32
• func CalcWork(bits uint32) *big.Int
• func CompactToBig(compact uint32) *big.Int
• func HashToBig(buf []byte) *big.Int

Functions

func BigToCompact

func BigToCompact(n *big.Int) uint32

BigToCompact converts a whole number N to a compact representation using an unsigned 32-bit number. The compact representation only provides 23 bits of precision, so values larger than (2^23 - 1) only encode the most significant digits of the number. See CompactToBig for details.

func CalcWork

func CalcWork(bits uint32) *big.Int

CalcWork calculates a work value from difficulty bits. Bitcoin increases the difficulty for generating a block by decreasing the value which the generated hash must be less than. This difficulty target is stored in each block header using a compact representation as described in the documentation for CompactToBig. The main chain is selected by choosing the chain that has the most proof of work (highest difficulty). Since a lower target difficulty value equates to higher actual difficulty, the work value which will be accumulated must be the inverse of the difficulty. Also, in order to avoid potential division by zero and really small floating point numbers, the result adds 1 to the denominator and multiplies the numerator by 2^256.

func CompactToBig

func CompactToBig(compact uint32) *big.Int

CompactToBig converts a compact representation of a whole number N to an unsigned 32-bit number. The representation is similar to IEEE754 floating point numbers.

Like IEEE754 floating point, there are three basic components: the sign, the exponent, and the mantissa. They are broken out as follows:

• the most significant 8 bits represent the unsigned base 256 exponent

• bit 23 (the 24th bit) represents the sign bit

• the least significant 23 bits represent the mantissa

  ------------------------------------------------- | Exponent | Sign | Mantissa | ------------------------------------------------- | 8 bits [31-24] | 1 bit [23] | 23 bits [22-00] | -------------------------------------------------

The formula to calculate N is:

N = (-1^sign) * mantissa * 256^(exponent-3)

This compact form is only used in bitcoin to encode unsigned 256-bit numbers which represent difficulty targets, thus there really is not a need for a sign bit, but it is implemented here to stay consistent with bitcoind.

func HashToBig

func HashToBig(buf []byte) *big.Int

HashToBig converts a chainhash.Hash into a big.Int that can be used to perform math comparisons.