ceremonyclient/pebble/internal/randvar/skewed_latest.go
Cassandra Heart 2e2a1e4789
v1.2.0 (#31)
2024-01-03 01:31:42 -06:00

78 lines
2.0 KiB
Go

// Copyright 2018 The Cockroach Authors.
//
// 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. See the AUTHORS file
// for names of contributors.
package randvar
import (
"sync"
"golang.org/x/exp/rand"
)
// SkewedLatest is a random number generator that generates numbers in
// the range [min, max], but skews it towards max using a zipfian
// distribution.
type SkewedLatest struct {
mu struct {
sync.RWMutex
max uint64
zipf *Zipf
}
}
// NewDefaultSkewedLatest constructs a new SkewedLatest generator with the
// default parameters.
func NewDefaultSkewedLatest() (*SkewedLatest, error) {
return NewSkewedLatest(1, defaultMax, defaultTheta)
}
// NewSkewedLatest constructs a new SkewedLatest generator with the given
// parameters. It returns an error if the parameters are outside the accepted
// range.
func NewSkewedLatest(min, max uint64, theta float64) (*SkewedLatest, error) {
z := &SkewedLatest{}
z.mu.max = max
zipf, err := NewZipf(0, max-min, theta)
if err != nil {
return nil, err
}
z.mu.zipf = zipf
return z, nil
}
// IncMax increments max.
func (z *SkewedLatest) IncMax(delta int) {
z.mu.Lock()
z.mu.zipf.IncMax(delta)
z.mu.max += uint64(delta)
z.mu.Unlock()
}
// Max returns max.
func (z *SkewedLatest) Max() uint64 {
z.mu.Lock()
defer z.mu.Unlock()
return z.mu.zipf.Max()
}
// Uint64 returns a random Uint64 between min and max, where keys near max are
// most likely to be drawn.
func (z *SkewedLatest) Uint64(rng *rand.Rand) uint64 {
z.mu.RLock()
result := z.mu.max - z.mu.zipf.Uint64(rng)
z.mu.RUnlock()
return result
}