47 lines
1.0 KiB
Go
47 lines
1.0 KiB
Go
// Copyright (C) 2019 Storj Labs, Inc.
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// See LICENSE for copying information.
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package audit
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import (
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"math/rand"
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"storj.io/common/storj"
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)
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const maxReservoirSize = 3
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// Reservoir holds a certain number of segments to reflect a random sample.
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type Reservoir struct {
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Paths [maxReservoirSize]storj.Path
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size int8
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index int64
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}
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// NewReservoir instantiates a Reservoir.
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func NewReservoir(size int) *Reservoir {
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if size < 1 {
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size = 1
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} else if size > maxReservoirSize {
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size = maxReservoirSize
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}
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return &Reservoir{
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size: int8(size),
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index: 0,
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}
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}
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// Sample makes sure that for every segment in metainfo from index i=size..n-1,
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// pick a random number r = rand(0..i), and if r < size, replace reservoir.Segments[r] with segment.
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func (reservoir *Reservoir) Sample(r *rand.Rand, path storj.Path) {
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reservoir.index++
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if reservoir.index < int64(reservoir.size) {
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reservoir.Paths[reservoir.index] = path
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} else {
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random := r.Int63n(reservoir.index)
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if random < int64(reservoir.size) {
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reservoir.Paths[random] = path
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}
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}
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}
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