op-geth/swarm/chunk/chunk.go

package chunk

import (
	"errors"
	"fmt"

	"github.com/ethereum/go-ethereum/common"
)

const (
	DefaultSize   = 4096
	MaxPO         = 16
	AddressLength = 32
)

var (
	ErrChunkNotFound = errors.New("chunk not found")
	ErrChunkInvalid  = errors.New("invalid chunk")
)

type Chunk interface {
	Address() Address
	Data() []byte
}

type chunk struct {
	addr  Address
	sdata []byte
}

func NewChunk(addr Address, data []byte) *chunk {
	return &chunk{
		addr:  addr,
		sdata: data,
	}
}

func (c *chunk) Address() Address {
	return c.addr
}

func (c *chunk) Data() []byte {
	return c.sdata
}

func (self *chunk) String() string {
	return fmt.Sprintf("Address: %v Chunksize: %v", self.addr.Log(), len(self.sdata))
}

type Address []byte

var ZeroAddr = Address(common.Hash{}.Bytes())

func (a Address) Hex() string {
	return fmt.Sprintf("%064x", []byte(a[:]))
}

func (a Address) Log() string {
	if len(a[:]) < 8 {
		return fmt.Sprintf("%x", []byte(a[:]))
	}
	return fmt.Sprintf("%016x", []byte(a[:8]))
}

func (a Address) String() string {
	return fmt.Sprintf("%064x", []byte(a))
}

func (a Address) MarshalJSON() (out []byte, err error) {
	return []byte(`"` + a.String() + `"`), nil
}

func (a *Address) UnmarshalJSON(value []byte) error {
	s := string(value)
	*a = make([]byte, 32)
	h := common.Hex2Bytes(s[1 : len(s)-1])
	copy(*a, h)
	return nil
}

// Proximity returns the proximity order of the MSB distance between x and y
//
// The distance metric MSB(x, y) of two equal length byte sequences x an y is the
// value of the binary integer cast of the x^y, ie., x and y bitwise xor-ed.
// the binary cast is big endian: most significant bit first (=MSB).
//
// Proximity(x, y) is a discrete logarithmic scaling of the MSB distance.
// It is defined as the reverse rank of the integer part of the base 2
// logarithm of the distance.
// It is calculated by counting the number of common leading zeros in the (MSB)
// binary representation of the x^y.
//
// (0 farthest, 255 closest, 256 self)
func Proximity(one, other []byte) (ret int) {
	b := (MaxPO-1)/8 + 1
	if b > len(one) {
		b = len(one)
	}
	m := 8
	for i := 0; i < b; i++ {
		oxo := one[i] ^ other[i]
		for j := 0; j < m; j++ {
			if (oxo>>uint8(7-j))&0x01 != 0 {
				return i*8 + j
			}
		}
	}
	return MaxPO
}