Generating entropy without imports in Go

entropy.go

// https://blog.merovius.de/2018/01/15/generating_entropy_without_imports_in_go.html

package main

import "fmt"

func main() {
	fmt.Println(MapIteration())
	fmt.Println(Select())
	fmt.Println(RaceCondition())
	fmt.Println(DataRace())
}

func MapIteration() string {
	var r rand

	m := make(map[uint32]bool)
	for i := uint32(0); i < 100; i++ {
		m[i] = true
	}
	for i := 0; i < 1000; i++ {
		for k := range m {
			r.mix(k)
			break // the rest of the loop is deterministic
		}
	}
	return hex(r.rand())
}

func Select() string {
	var r rand

	ch := make(chan bool)
	close(ch)
	for i := 0; i < 1000; i++ {
		select {
		case <-ch:
			r.mix(1)
		case <-ch:
			r.mix(2)
		}
	}
	return hex(r.rand())
}

func RaceCondition() string {
	var r rand

	for i := 0; i < 1000; i++ {
		ch := make(chan uint32, 2)
		start := make(chan bool)
		go func() {
			<-start
			ch <- 1
		}()
		go func() {
			<-start
			ch <- 2
		}()
		close(start)
		r.mix(<-ch)
	}

	return hex(r.rand())
}

func DataRace() string {
	var r rand

	var data *uintptr
	var addr *uintptr

	var i, j, k interface{}
	i = (*uintptr)(nil)
	j = &data

	done := false
	go func() {
		for !done {
			k = i
			k = j
		}
	}()
	for {
		if p, ok := k.(*uintptr); ok && p != nil {
			addr = p
			done = true
			break
		}
	}

	data = new(uintptr)
	r.mix(uint32(*addr))
	return hex(r.rand())
}

type rand uint32

func (r *rand) mix(v uint32) {
	*r = ((*r << 5) + *r) + rand(v)
}

func (r *rand) rand() uint32 {
	mx := rand(int32(*r)>>31) & 0xa8888eef
	*r = *r<<1 ^ mx
	return uint32(*r)
}

func hex(v uint32) string {
	var b []byte
	for v != 0 {
		if x := byte(v & 0xf); x < 10 {
			b = append(b, '0'+x)
		} else {
			b = append(b, 'a'+x-10)
		}
		v >>= 4
	}
	return string(b)
}