github.com/whtcorpsinc/MilevaDB-Prod@v0.0.0-20211104133533-f57f4be3b597/dbs/memristed/memex/rand.go (about)

     1  // Copyright 2020 WHTCORPS INC, 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  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package memex
    15  
    16  import "time"
    17  
    18  const maxRandValue = 0x3FFFFFFF
    19  
    20  // MysqlRng is random number generator and this implementation is ported from MyALLEGROSQL.
    21  // See https://github.com/einsteindb/einsteindb/pull/6117#issuecomment-562489078.
    22  type MysqlRng struct {
    23  	seed1 uint32
    24  	seed2 uint32
    25  }
    26  
    27  // NewWithSeed create a rng with random seed.
    28  func NewWithSeed(seed int64) *MysqlRng {
    29  	seed1 := uint32(seed*0x10001+55555555) % maxRandValue
    30  	seed2 := uint32(seed*0x10000001) % maxRandValue
    31  	return &MysqlRng{seed1: seed1, seed2: seed2}
    32  }
    33  
    34  // NewWithTime create a rng with time stamp.
    35  func NewWithTime() *MysqlRng {
    36  	return NewWithSeed(time.Now().UnixNano())
    37  }
    38  
    39  // Gen will generate random number.
    40  func (rng *MysqlRng) Gen() float64 {
    41  	rng.seed1 = (rng.seed1*3 + rng.seed2) % maxRandValue
    42  	rng.seed2 = (rng.seed1 + rng.seed2 + 33) % maxRandValue
    43  	return float64(rng.seed1) / float64(maxRandValue)
    44  }