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uniform_replacer.go
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uniform_replacer.go
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// Copyright (C) 2019-2023, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package sampler
import "golang.org/x/exp/maps"
type defaultMap map[uint64]uint64
func (m defaultMap) get(key uint64, defaultVal uint64) uint64 {
if val, ok := m[key]; ok {
return val
}
return defaultVal
}
// uniformReplacer allows for sampling over a uniform distribution without
// replacement.
//
// Sampling is performed by lazily performing an array shuffle of the array
// [0, 1, ..., length - 1]. By performing the first count swaps of this shuffle,
// we can create an array of length count with elements sampled with uniform
// probability.
//
// Initialization takes O(1) time.
//
// Sampling is performed in O(count) time and O(count) space.
type uniformReplacer struct {
rng *rng
seededRNG *rng
length uint64
drawn defaultMap
drawsCount uint64
}
func (s *uniformReplacer) Initialize(length uint64) {
s.rng = globalRNG
s.seededRNG = newRNG()
s.length = length
s.drawn = make(defaultMap)
s.drawsCount = 0
}
func (s *uniformReplacer) Sample(count int) ([]uint64, error) {
s.Reset()
results := make([]uint64, count)
for i := 0; i < count; i++ {
ret, err := s.Next()
if err != nil {
return nil, err
}
results[i] = ret
}
return results, nil
}
func (s *uniformReplacer) Seed(seed int64) {
s.rng = s.seededRNG
s.rng.Seed(seed)
}
func (s *uniformReplacer) ClearSeed() {
s.rng = globalRNG
}
func (s *uniformReplacer) Reset() {
maps.Clear(s.drawn)
s.drawsCount = 0
}
func (s *uniformReplacer) Next() (uint64, error) {
if s.drawsCount >= s.length {
return 0, ErrOutOfRange
}
draw := s.rng.Uint64Inclusive(s.length-1-s.drawsCount) + s.drawsCount
ret := s.drawn.get(draw, draw)
s.drawn[draw] = s.drawn.get(s.drawsCount, s.drawsCount)
s.drawsCount++
return ret, nil
}