gno.land/p/moul/entropy/v0⧉

1// Entropy generates fully deterministic, cost-effective, and hard to guess2// numbers.3//4// It is designed both for single-usage, like seeding math/rand or for being5// reused which increases the entropy and its cost effectiveness.6//7// Disclaimer: this package is unsafe and won't prevent others to guess values8// in advance.9//10// It uses the Bernstein's hash djb2 to be CPU-cycle efficient.11package entropy1213import (14	"chain/runtime"15	"chain/runtime/unsafe"16	"math"17	"time"18)1920type Instance struct {21	value uint3222}2324func New() *Instance {25	r := Instance{value: 5381}26	r.addEntropy()27	return &r28}2930func FromSeed(seed uint32) *Instance {31	r := Instance{value: seed}32	r.addEntropy()33	return &r34}3536func (i *Instance) Seed() uint32 {37	return i.value38}3940func (i *Instance) djb2String(input string) {41	for _, c := range input {42		i.djb2Uint32(uint32(c))43	}44}4546// super fast random algorithm.47// http://www.cse.yorku.ca/~oz/hash.html48func (i *Instance) djb2Uint32(input uint32) {49	i.value = (i.value << 5) + i.value + input50}5152// AddEntropy uses various runtime variables to add entropy to the existing seed.53func (i *Instance) addEntropy() {54	// FIXME: reapply the 5381 initial value?5556	// inherit previous entropy57	// nothing to do5859	// handle callers60	{61		currentRealm := unsafe.CurrentRealm().Address().String()62		i.djb2String(currentRealm)63		originCaller := unsafe.OriginCaller().String()64		i.djb2String(originCaller)65	}6667	// height68	{69		height := runtime.ChainHeight()70		if height >= math.MaxUint32 {71			height -= math.MaxUint3272		}73		i.djb2Uint32(uint32(height))74	}7576	// time77	{78		secs := time.Now().Second()79		i.djb2Uint32(uint32(secs))80		nsecs := time.Now().Nanosecond()81		i.djb2Uint32(uint32(nsecs))82	}8384	// FIXME: compute other hard-to-guess but deterministic variables, like real gas?85}8687func (i *Instance) Value() uint32 {88	i.addEntropy()89	return i.value90}9192func (i *Instance) Value64() uint64 {93	i.addEntropy()94	high := i.value95	i.addEntropy()9697	return (uint64(high) << 32) | uint64(i.value)98}99