Faster source for math/rand/v2 based on runtime rand

runtime_source.go

// License: CC0
package frs

import (
	"hash/maphash"
	"unsafe"
)

// RuntimeSource is a non-reproducible, cryptographically insecure math/rand/v2 pseudorandom source.
// Based on maphash.MakeSeed that exports runtime rand, with the output based on the internal per-G state of the runtime,
// which is unknown to userspace, shared per-G and therefore cannot be exported for reproduction.
//
// WARNING: Do not use this for cryptographical usages. Use crypto/rand instead.
type RuntimeSource struct{}

func (s RuntimeSource) Uint64() uint64 {
	type seed struct {
		s uint64
	}
	r := maphash.MakeSeed()
	return (*seed)(unsafe.Pointer(&r)).s
}