Update dependencies

vendor/tailscale.com/util/rands/cheap.go

@@ -0,0 +1,90 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package rands
+
+import (
+	"math/bits"
+
+	randv2 "math/rand/v2"
+)
+
+// Shuffle is like rand.Shuffle, but it does not allocate or lock any RNG state.
+func Shuffle[T any](seed uint64, data []T) {
+	var pcg randv2.PCG
+	pcg.Seed(seed, seed)
+	for i := len(data) - 1; i > 0; i-- {
+		j := int(uint64n(&pcg, uint64(i+1)))
+		data[i], data[j] = data[j], data[i]
+	}
+}
+
+// IntN is like rand.IntN, but it is seeded on the stack and does not allocate
+// or lock any RNG state.
+func IntN(seed uint64, n int) int {
+	var pcg randv2.PCG
+	pcg.Seed(seed, seed)
+	return int(uint64n(&pcg, uint64(n)))
+}
+
+// Perm is like rand.Perm, but it is seeded on the stack and does not allocate
+// or lock any RNG state.
+func Perm(seed uint64, n int) []int {
+	p := make([]int, n)
+	for i := range p {
+		p[i] = i
+	}
+	Shuffle(seed, p)
+	return p
+}
+
+// uint64n is the no-bounds-checks version of rand.Uint64N from the standard
+// library. 32-bit optimizations have been elided.
+func uint64n(pcg *randv2.PCG, n uint64) uint64 {
+	if n&(n-1) == 0 { // n is power of two, can mask
+		return pcg.Uint64() & (n - 1)
+	}
+
+	// Suppose we have a uint64 x uniform in the range [0,2⁶⁴)
+	// and want to reduce it to the range [0,n) preserving exact uniformity.
+	// We can simulate a scaling arbitrary precision x * (n/2⁶⁴) by
+	// the high bits of a double-width multiply of x*n, meaning (x*n)/2⁶⁴.
+	// Since there are 2⁶⁴ possible inputs x and only n possible outputs,
+	// the output is necessarily biased if n does not divide 2⁶⁴.
+	// In general (x*n)/2⁶⁴ = k for x*n in [k*2⁶⁴,(k+1)*2⁶⁴).
+	// There are either floor(2⁶⁴/n) or ceil(2⁶⁴/n) possible products
+	// in that range, depending on k.
+	// But suppose we reject the sample and try again when
+	// x*n is in [k*2⁶⁴, k*2⁶⁴+(2⁶⁴%n)), meaning rejecting fewer than n possible
+	// outcomes out of the 2⁶⁴.
+	// Now there are exactly floor(2⁶⁴/n) possible ways to produce
+	// each output value k, so we've restored uniformity.
+	// To get valid uint64 math, 2⁶⁴ % n = (2⁶⁴ - n) % n = -n % n,
+	// so the direct implementation of this algorithm would be:
+	//
+	//	hi, lo := bits.Mul64(r.Uint64(), n)
+	//	thresh := -n % n
+	//	for lo < thresh {
+	//		hi, lo = bits.Mul64(r.Uint64(), n)
+	//	}
+	//
+	// That still leaves an expensive 64-bit division that we would rather avoid.
+	// We know that thresh < n, and n is usually much less than 2⁶⁴, so we can
+	// avoid the last four lines unless lo < n.
+	//
+	// See also:
+	// https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction
+	// https://lemire.me/blog/2016/06/30/fast-random-shuffling
+	hi, lo := bits.Mul64(pcg.Uint64(), n)
+	if lo < n {
+		thresh := -n % n
+		for lo < thresh {
+			hi, lo = bits.Mul64(pcg.Uint64(), n)
+		}
+	}
+	return hi
+}

vendor/tailscale.com/util/rands/rands.go

@@ -0,0 +1,25 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package rands contains utility functions for randomness.
+package rands
+
+import (
+	crand "crypto/rand"
+	"encoding/hex"
+)
+
+// HexString returns a string of n cryptographically random lowercase
+// hex characters.
+//
+// That is, HexString(3) returns something like "0fc", containing 12
+// bits of randomness.
+func HexString(n int) string {
+	nb := n / 2
+	if n%2 == 1 {
+		nb++
+	}
+	b := make([]byte, nb)
+	crand.Read(b)
+	return hex.EncodeToString(b)[:n]
+}