rand.go

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.
varFastRander=newRBG()

funcnewRBG() io.Reader {
r, err:=newRandomBitsGenerator()
iferr!=nil {
panic(err)
 }
returnr
}

funcnewRandomBitsGenerator() (r io.Reader, errerror) {
varseedint64

ifseed, err=readCryptoRandomSeed(); err!=nil {
return
 }

r=&randSourceReader{source: rand.NewSource(seed).(rand.Source64)}
return
}

funcreadCryptoRandomSeed() (seedint64, errerror) {
varb [8]byte

if_, err=io.ReadFull(cryptoRand.Reader, b[:]); err!=nil {
return
 }

seed=int64(binary.LittleEndian.Uint64(b[:]))
return
}

typerandSourceReaderstruct {
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())
return16, nil
}