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-- import ""

Package fastuuid provides fast UUID generation of 192 bit universally unique identifiers.

It also provides simple support for 128-bit RFC-4122 V4 UUID strings.

Note that the generated UUIDs are not unguessable - each UUID generated from a Generator is adjacent to the previously generated UUID.

By way of comparison with two other popular UUID-generation packages, and, here are some benchmarks:

BenchmarkNext-4              	128272185	         9.20 ns/op
BenchmarkHex128-4            	14323180	        76.4 ns/op
BenchmarkContended-4         	45741997	        26.4 ns/op
BenchmarkSatoriNext-4        	 1231281	       967 ns/op
BenchmarkSatoriHex128-4      	 1000000	      1041 ns/op
BenchmarkSatoriContended-4   	 1765520	       666 ns/op
BenchmarkGoogleNext-4        	 1256250	       958 ns/op
BenchmarkGoogleHex128-4      	 1000000	      1044 ns/op
BenchmarkGoogleContended-4   	 1746570	       690 ns/op


func Hex128

func Hex128(uuid [24]byte) string

Hex128 returns an RFC4122 V4 representation of the first 128 bits of the given UUID. For example:


Note: before encoding, it swaps bytes 6 and 9 so that all the varying bits of the UUID as returned from Generator.Next are reflected in the Hex128 representation.

If you want unpredictable UUIDs, you might want to consider hashing the uuid (using SHA256, for example) before passing it to Hex128.

func ValidHex128

func ValidHex128(id string) bool

ValidHex128 reports whether id is a valid UUID as returned by Hex128 and various other UUID packages, such as's NewV4 function.

Note that it does not allow upper case hex.

type Generator

type Generator struct {

Generator represents a UUID generator that generates UUIDs in sequence from a random starting point.

func MustNewGenerator

func MustNewGenerator() *Generator

MustNewGenerator is like NewGenerator but panics on failure.

func NewGenerator

func NewGenerator() (*Generator, error)

NewGenerator returns a new Generator. It can fail if the crypto/rand read fails.

func (*Generator) Hex128

func (g *Generator) Hex128() string

Hex128 is a convenience method that returns Hex128(g.Next()).

func (*Generator) Next

func (g *Generator) Next() [24]byte

Next returns the next UUID from the generator. Only the first 8 bytes can differ from the previous UUID, so taking a slice of the first 16 bytes is sufficient to provide a somewhat less secure 128 bit UUID.

It is OK to call this method concurrently.


Fast generation of 192-bit UUIDs







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