github.com/vescale/zgraph@v0.0.0-20230410094002-959c02d50f95/internal/mathutil/rand.go (about)

     1  // Copyright 2020 PingCAP, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package mathutil
    16  
    17  import (
    18  	"sync"
    19  	"time"
    20  )
    21  
    22  const maxRandValue = 0x3FFFFFFF
    23  
    24  // MysqlRng is random number generator and this implementation is ported from MySQL.
    25  // See https://github.com/tikv/tikv/pull/6117#issuecomment-562489078.
    26  type MysqlRng struct {
    27  	mu    *sync.Mutex
    28  	seed1 uint32
    29  	seed2 uint32
    30  }
    31  
    32  // NewWithSeed create a rng with random seed.
    33  func NewWithSeed(seed int64) *MysqlRng {
    34  	seed1 := uint32(seed*0x10001+55555555) % maxRandValue
    35  	seed2 := uint32(seed*0x10000001) % maxRandValue
    36  	return &MysqlRng{
    37  		seed1: seed1,
    38  		seed2: seed2,
    39  		mu:    &sync.Mutex{},
    40  	}
    41  }
    42  
    43  // NewWithTime create a rng with time stamp.
    44  func NewWithTime() *MysqlRng {
    45  	return NewWithSeed(time.Now().UnixNano())
    46  }
    47  
    48  // Gen will generate random number.
    49  func (rng *MysqlRng) Gen() float64 {
    50  	rng.mu.Lock()
    51  	defer rng.mu.Unlock()
    52  	rng.seed1 = (rng.seed1*3 + rng.seed2) % maxRandValue
    53  	rng.seed2 = (rng.seed1 + rng.seed2 + 33) % maxRandValue
    54  	return float64(rng.seed1) / float64(maxRandValue)
    55  }
    56  
    57  // SetSeed1 is a interface to set seed1
    58  func (rng *MysqlRng) SetSeed1(seed uint32) {
    59  	rng.mu.Lock()
    60  	defer rng.mu.Unlock()
    61  	rng.seed1 = seed
    62  }
    63  
    64  // SetSeed2 is a interface to set seed2
    65  func (rng *MysqlRng) SetSeed2(seed uint32) {
    66  	rng.mu.Lock()
    67  	defer rng.mu.Unlock()
    68  	rng.seed2 = seed
    69  }
    70  
    71  // GetSeed1 is an interface to get seed1. It's only used for getting session states.
    72  func (rng *MysqlRng) GetSeed1() uint32 {
    73  	rng.mu.Lock()
    74  	defer rng.mu.Unlock()
    75  	return rng.seed1
    76  }
    77  
    78  // GetSeed2 is an interface to get seed2. It's only used for getting session states.
    79  func (rng *MysqlRng) GetSeed2() uint32 {
    80  	rng.mu.Lock()
    81  	defer rng.mu.Unlock()
    82  	return rng.seed2
    83  }