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