github.com/cockroachdb/pebble@v1.1.1-0.20240513155919-3622ade60459/internal/randvar/uniform.go (about)

     1  // Copyright 2018 The Cockroach Authors.
     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
    12  // implied. See the License for the specific language governing
    13  // permissions and limitations under the License. See the AUTHORS file
    14  // for names of contributors.
    15  
    16  package randvar
    17  
    18  import (
    19  	"sync/atomic"
    20  
    21  	"golang.org/x/exp/rand"
    22  )
    23  
    24  // Uniform is a random number generator that generates draws from a uniform
    25  // distribution.
    26  type Uniform struct {
    27  	min uint64
    28  	max atomic.Uint64
    29  }
    30  
    31  // NewUniform constructs a new Uniform generator with the given
    32  // parameters. Returns an error if the parameters are outside the accepted
    33  // range.
    34  func NewUniform(min, max uint64) *Uniform {
    35  	u := &Uniform{min: min}
    36  	u.max.Store(max)
    37  	return u
    38  }
    39  
    40  // IncMax increments max.
    41  func (g *Uniform) IncMax(delta int) {
    42  	g.max.Add(uint64(delta))
    43  }
    44  
    45  // Max returns the max value of the distribution.
    46  func (g *Uniform) Max() uint64 {
    47  	return g.max.Load()
    48  }
    49  
    50  // Uint64 returns a random Uint64 between min and max, drawn from a uniform
    51  // distribution.
    52  func (g *Uniform) Uint64(rng *rand.Rand) uint64 {
    53  	return rng.Uint64n(g.Max()-g.min+1) + g.min
    54  }