tidb random 代码
文件路径：/util/fastrand/random.go
/ Copyright 2017 PingCAP, Inc.
/
/ Licensed under the Apache License, Version 2.0 (the "License");
/ you may not use this file except in compliance with the License.
/ You may obtain a copy of the License at
/
/ http://www.apache.org/licenses/LICENSE-2.0
/
/ Unless required by applicable law or agreed to in writing, software
/ distributed under the License is distributed on an "AS IS" BASIS,
/ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/ See the License for the specific language governing permissions and
/ limitations under the License.
package fastrand
import (
"math/bits"
_ "unsafe" / required by go:linkname
)
/ wyrand is a fast PRNG. See https://github.com/wangyi-fudan/wyhash
type wyrand uint64
func _wymix(a, b uint64) uint64 {
hi, lo := bits.Mul64(a, b)
return hi ^ lo
}
func (r *wyrand) Next() uint64 {
*r += wyrand(0xa0761d6478bd642f)
return _wymix(uint64(*r), uint64(*r^wyrand(0xe7037ed1a0b428db)))
}
/ Buf generates a random string using ASCII characters but avoid separator character.
/ See https://github.com/mysql/mysql-server/blob/5.7/mysys_ssl/crypt_genhash_impl.cc#L435
func Buf(size int) []byte {
buf := make([]byte, size)
r := wyrand(Uint32())
for i := 0; i < size; i++ {
/ This is similar to Uint32() % n, but faster.
/ See https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
buf[i] = byte(uint32(uint64(uint32(r.Next())) * uint64(127) >> 32))
if buf[i] == 0 || buf[i] == byte('$') {
buf[i]++
}
}
return buf
}
/ Uint32 returns a lock free uint32 value.
/
/go:linkname Uint32 runtime.fastrand
func Uint32() uint32
/ Uint32N returns, as an uint32, a pseudo-random number in [0,n).
func Uint32N(n uint32) uint32 {
/ This is similar to Uint32() % n, but faster.
/ See https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
return uint32(uint64(Uint32()) * uint64(n) >> 32)
}
/ Uint64N returns, as an uint64, a pseudo-random number in [0,n).
func Uint64N(n uint64) uint64 {
a := Uint32()
b := Uint32()
v := uint64(a)<<32 + uint64(b)
if n&(n-1) == 0 { / n is power of two, can mask
return v & (n - 1)
}
return v % n
}