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45 lines
1.0 KiB
Go
45 lines
1.0 KiB
Go
// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package tstime
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import (
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crand "crypto/rand"
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"encoding/binary"
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"math/rand"
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"sync"
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"time"
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)
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// crandSource is a rand.Source64 that gets its numbers from
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// crypto/rand.Reader.
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type crandSource struct{ sync.Mutex }
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var _ rand.Source64 = (*crandSource)(nil)
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func (s *crandSource) Int63() int64 { return int64(s.Uint64() >> 1) }
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func (s *crandSource) Uint64() uint64 {
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s.Lock()
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defer s.Unlock()
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var buf [8]byte
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crand.Read(buf[:])
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return binary.BigEndian.Uint64(buf[:])
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}
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func (*crandSource) Seed(seed int64) {} // nope
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var durRand = rand.New(new(crandSource))
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// RandomDurationBetween returns a random duration in range [min,max).
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// If panics if max < min.
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func RandomDurationBetween(min, max time.Duration) time.Duration {
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diff := max - min
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if diff == 0 {
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return min
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}
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ns := durRand.Int63n(int64(diff))
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return min + time.Duration(ns)
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}
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