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package ksuid
import (
cryptoRand "crypto/rand"
"encoding/binary"
"io"
"math/rand"
)
// FastRander is an io.Reader that uses math/rand and is optimized for
// generating 16 bytes KSUID payloads. It is intended to be used as a
// performance improvements for programs that have no need for
// cryptographically secure KSUIDs and are generating a lot of them.
var FastRander = newRBG()
func newRBG() io.Reader {
r, err := newRandomBitsGenerator()
if err != nil {
panic(err)
}
return r
}
func newRandomBitsGenerator() (r io.Reader, err error) {
var seed int64
if seed, err = readCryptoRandomSeed(); err != nil {
return
}
r = &randSourceReader{source: rand.NewSource(seed).(rand.Source64)}
return
}
func readCryptoRandomSeed() (seed int64, err error) {
var b [8]byte
if _, err = io.ReadFull(cryptoRand.Reader, b[:]); err != nil {
return
}
seed = int64(binary.LittleEndian.Uint64(b[:]))
return
}
type randSourceReader struct {
source rand.Source64
}
func (r *randSourceReader) Read(b []byte) (int, error) {
// optimized for generating 16 bytes payloads
binary.LittleEndian.PutUint64(b[:8], r.source.Uint64())
binary.LittleEndian.PutUint64(b[8:], r.source.Uint64())
return 16, nil
}
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