bits

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Version: v0.0.14 Latest Latest
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Published: Apr 17, 2021 License: Unlicense Imports: 1 Imported by: 0

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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 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.

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