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This file was never truly necessary and has never actually been used in the history of Tailscale's open source releases. A Brief History of AUTHORS files --- The AUTHORS file was a pattern developed at Google, originally for Chromium, then adopted by Go and a bunch of other projects. The problem was that Chromium originally had a copyright line only recognizing Google as the copyright holder. Because Google (and most open source projects) do not require copyright assignemnt for contributions, each contributor maintains their copyright. Some large corporate contributors then tried to add their own name to the copyright line in the LICENSE file or in file headers. This quickly becomes unwieldy, and puts a tremendous burden on anyone building on top of Chromium, since the license requires that they keep all copyright lines intact. The compromise was to create an AUTHORS file that would list all of the copyright holders. The LICENSE file and source file headers would then include that list by reference, listing the copyright holder as "The Chromium Authors". This also become cumbersome to simply keep the file up to date with a high rate of new contributors. Plus it's not always obvious who the copyright holder is. Sometimes it is the individual making the contribution, but many times it may be their employer. There is no way for the proejct maintainer to know. Eventually, Google changed their policy to no longer recommend trying to keep the AUTHORS file up to date proactively, and instead to only add to it when requested: https://opensource.google/docs/releasing/authors. They are also clear that: > Adding contributors to the AUTHORS file is entirely within the > project's discretion and has no implications for copyright ownership. It was primarily added to appease a small number of large contributors that insisted that they be recognized as copyright holders (which was entirely their right to do). But it's not truly necessary, and not even the most accurate way of identifying contributors and/or copyright holders. In practice, we've never added anyone to our AUTHORS file. It only lists Tailscale, so it's not really serving any purpose. It also causes confusion because Tailscalars put the "Tailscale Inc & AUTHORS" header in other open source repos which don't actually have an AUTHORS file, so it's ambiguous what that means. Instead, we just acknowledge that the contributors to Tailscale (whoever they are) are copyright holders for their individual contributions. We also have the benefit of using the DCO (developercertificate.org) which provides some additional certification of their right to make the contribution. The source file changes were purely mechanical with: git ls-files | xargs sed -i -e 's/\(Tailscale Inc &\) AUTHORS/\1 contributors/g' Updates #cleanup Change-Id: Ia101a4a3005adb9118051b3416f5a64a4a45987d Signed-off-by: Will Norris <will@tailscale.com>
91 lines
2.9 KiB
Go
91 lines
2.9 KiB
Go
// Copyright (c) Tailscale Inc & contributors
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// SPDX-License-Identifier: BSD-3-Clause
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// Copyright 2009 The Go 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 rands
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import (
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"math/bits"
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randv2 "math/rand/v2"
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)
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// Shuffle is like rand.Shuffle, but it does not allocate or lock any RNG state.
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func Shuffle[T any](seed uint64, data []T) {
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var pcg randv2.PCG
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pcg.Seed(seed, seed)
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for i := len(data) - 1; i > 0; i-- {
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j := int(uint64n(&pcg, uint64(i+1)))
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data[i], data[j] = data[j], data[i]
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}
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}
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// IntN is like rand.IntN, but it is seeded on the stack and does not allocate
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// or lock any RNG state.
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func IntN(seed uint64, n int) int {
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var pcg randv2.PCG
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pcg.Seed(seed, seed)
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return int(uint64n(&pcg, uint64(n)))
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}
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// Perm is like rand.Perm, but it is seeded on the stack and does not allocate
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// or lock any RNG state.
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func Perm(seed uint64, n int) []int {
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p := make([]int, n)
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for i := range p {
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p[i] = i
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}
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Shuffle(seed, p)
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return p
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}
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// uint64n is the no-bounds-checks version of rand.Uint64N from the standard
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// library. 32-bit optimizations have been elided.
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func uint64n(pcg *randv2.PCG, n uint64) uint64 {
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if n&(n-1) == 0 { // n is power of two, can mask
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return pcg.Uint64() & (n - 1)
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}
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// Suppose we have a uint64 x uniform in the range [0,2⁶⁴)
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// and want to reduce it to the range [0,n) preserving exact uniformity.
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// We can simulate a scaling arbitrary precision x * (n/2⁶⁴) by
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// the high bits of a double-width multiply of x*n, meaning (x*n)/2⁶⁴.
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// Since there are 2⁶⁴ possible inputs x and only n possible outputs,
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// the output is necessarily biased if n does not divide 2⁶⁴.
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// In general (x*n)/2⁶⁴ = k for x*n in [k*2⁶⁴,(k+1)*2⁶⁴).
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// There are either floor(2⁶⁴/n) or ceil(2⁶⁴/n) possible products
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// in that range, depending on k.
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// But suppose we reject the sample and try again when
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// x*n is in [k*2⁶⁴, k*2⁶⁴+(2⁶⁴%n)), meaning rejecting fewer than n possible
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// outcomes out of the 2⁶⁴.
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// Now there are exactly floor(2⁶⁴/n) possible ways to produce
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// each output value k, so we've restored uniformity.
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// To get valid uint64 math, 2⁶⁴ % n = (2⁶⁴ - n) % n = -n % n,
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// so the direct implementation of this algorithm would be:
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//
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// hi, lo := bits.Mul64(r.Uint64(), n)
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// thresh := -n % n
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// for lo < thresh {
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// hi, lo = bits.Mul64(r.Uint64(), n)
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// }
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//
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// That still leaves an expensive 64-bit division that we would rather avoid.
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// We know that thresh < n, and n is usually much less than 2⁶⁴, so we can
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// avoid the last four lines unless lo < n.
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//
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// See also:
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// https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction
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// https://lemire.me/blog/2016/06/30/fast-random-shuffling
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hi, lo := bits.Mul64(pcg.Uint64(), n)
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if lo < n {
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thresh := -n % n
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for lo < thresh {
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hi, lo = bits.Mul64(pcg.Uint64(), n)
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}
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}
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return hi
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}
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