time.Now().UnixNano
这是用的最多的，但是，也是安全隐患最大的方法。
从表面上看go的时间方法最大精度到纳秒，但是好像其实并不能到达的绝对的纳秒精度。
测试结果很不好，碰撞很高。
import "time"
func TestSeedNanoTime(t *testing.T) {
var seeds = make(map[int64]bool)
for i := 0; i < 100000; i++ {
seed := time.Now().UnixNano()
seeds[seed] = true
fmt.Println(seed)
}
fmt.Println(len(seeds))
}
maphash.Hash
此方法无碰撞
import "hash/maphash"
func TestSeedMapHash(t *testing.T) {
var seeds = make(map[int64]bool)
for i := 0; i < 100000; i++ {
seed := int64(new(maphash.Hash).Sum64())
seeds[seed] = true
fmt.Println(seed)
}
fmt.Println(len(seeds))
}
cryptoRand.Read
该方法无碰撞
import (
cryptoRand "crypto/rand"
mathRand "math/rand"
)
func TestSeedCryptoRand(t *testing.T) {
var seeds = make(map[int64]bool)
for i := 0; i < 100000; i++ {
var b [8]byte
_, err := cryptoRand.Read(b[:])
if err != nil {
panic("cannot seed math/rand package with cryptographically secure random number generator")
}
seed := int64(binary.LittleEndian.Uint64(b[:]))
seeds[seed] = true
fmt.Println(seed)
}
fmt.Println(len(seeds))
}
映射表
该方法无碰撞
func TestSeedRandomString(t *testing.T) {
const alpha = "abcdefghijkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ23456789"
size := 8
var seeds = make(map[int64]bool)
for i := 0; i < 100000; i++ {
buf := make([]byte, size)
for i := 0; i < size; i++ {
buf[i] = alpha[mathRand.Intn(len(alpha))]
}
seed := int64(binary.LittleEndian.Uint64(buf[:]))
seeds[seed] = true
fmt.Println(seed)
}
fmt.Println(len(seeds))
}
