Merge pull request #339 from mrd0ll4r/xorshift
pkg/xorshift: rebuild to use stack only
This commit is contained in:
mrd0ll4r
GitHub
commit
d43cb719b9
6 changed files with 92 additions and 132 deletions
17
middleware/pkg/random/entropy.go
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17
middleware/pkg/random/entropy.go
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@ -0,0 +1,17 @@
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package random
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import (
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"encoding/binary"
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"github.com/chihaya/chihaya/bittorrent"
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)
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// DeriveEntropyFromRequest generates 2*64 bits of pseudo random state from an
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// AnnounceRequest.
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//
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// Calling DeriveEntropyFromRequest multiple times yields the same values.
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func DeriveEntropyFromRequest(req *bittorrent.AnnounceRequest) (uint64, uint64) {
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v0 := binary.BigEndian.Uint64([]byte(req.InfoHash[:8])) + binary.BigEndian.Uint64([]byte(req.InfoHash[8:16]))
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v1 := binary.BigEndian.Uint64([]byte(req.Peer.ID[:8])) + binary.BigEndian.Uint64([]byte(req.Peer.ID[8:16]))
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return v0, v1
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}
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28
middleware/pkg/random/xorshift.go
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28
middleware/pkg/random/xorshift.go
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@ -0,0 +1,28 @@
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// Package random implements the XORShift PRNG and a way to derive random state
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// from an AnnounceRequest.
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package random
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// GenerateAndAdvance applies XORShift128Plus on s0 and s1, returning
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// the new states newS0, newS1 and a pseudo-random number v.
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func GenerateAndAdvance(s0, s1 uint64) (v, newS0, newS1 uint64) {
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v = s0 + s1
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newS0 = s1
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s0 ^= (s0 << 23)
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newS1 = s0 ^ s1 ^ (s0 >> 18) ^ (s1 >> 5)
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return
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}
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// Intn generates an int k that satisfies k >= 0 && k < n.
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// n must be > 0.
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// It returns the generated k and the new state of the generator.
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func Intn(s0, s1 uint64, n int) (int, uint64, uint64) {
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if n <= 0 {
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panic("invalid n <= 0")
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}
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v, newS0, newS1 := GenerateAndAdvance(s0, s1)
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k := int(v)
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if k < 0 {
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k = -k
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}
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return k % n, newS0, newS1
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}
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38
middleware/pkg/random/xorshift_test.go
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38
middleware/pkg/random/xorshift_test.go
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@ -0,0 +1,38 @@
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package random
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import (
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"math/rand"
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"testing"
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"time"
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"github.com/stretchr/testify/require"
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)
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func TestIntn(t *testing.T) {
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rand.Seed(time.Now().UnixNano())
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s0, s1 := rand.Uint64(), rand.Uint64()
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var k int
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for i := 0; i < 10000; i++ {
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k, s0, s1 = Intn(s0, s1, 10)
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require.True(t, k >= 0, "Intn() must be >= 0")
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require.True(t, k < 10, "Intn(k) must be < k")
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}
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}
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func BenchmarkAdvanceXORShift128Plus(b *testing.B) {
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s0, s1 := rand.Uint64(), rand.Uint64()
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var v uint64
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for i := 0; i < b.N; i++ {
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v, s0, s1 = GenerateAndAdvance(s0, s1)
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}
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_, _, _ = v, s0, s1
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}
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func BenchmarkIntn(b *testing.B) {
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s0, s1 := rand.Uint64(), rand.Uint64()
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var v int
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for i := 0; i < b.N; i++ {
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v, s0, s1 = Intn(s0, s1, 1000)
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}
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_, _, _ = v, s0, s1
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}
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@ -3,13 +3,12 @@ package varinterval
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import (
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"context"
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"errors"
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"math/rand"
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"sync"
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"time"
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"github.com/chihaya/chihaya/bittorrent"
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"github.com/chihaya/chihaya/middleware"
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"github.com/chihaya/chihaya/pkg/xorshift"
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"github.com/chihaya/chihaya/middleware/pkg/random"
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)
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// ErrInvalidModifyResponseProbability is returned for a config with an invalid
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@ -48,7 +47,6 @@ func checkConfig(cfg Config) error {
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type hook struct {
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cfg Config
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pr [1024]*xorshift.LockedXORShift128Plus
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sync.Mutex
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}
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@ -62,23 +60,19 @@ func New(cfg Config) (middleware.Hook, error) {
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h := &hook{
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cfg: cfg,
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pr: [1024]*xorshift.LockedXORShift128Plus{},
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}
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for i := range h.pr {
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h.pr[i] = xorshift.NewLockedXORShift128Plus(rand.Uint64(), rand.Uint64())
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}
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return h, nil
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}
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func (h *hook) getXORShiftByInfohash(ih *bittorrent.InfoHash) *xorshift.LockedXORShift128Plus {
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return h.pr[(int(ih[1])|int(ih[0])<<8)%len(h.pr)]
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}
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func (h *hook) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequest, resp *bittorrent.AnnounceResponse) (context.Context, error) {
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r := h.getXORShiftByInfohash(&req.InfoHash)
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if h.cfg.ModifyResponseProbability == 1 || float32(xorshift.Intn(r, 1<<24))/(1<<24) < h.cfg.ModifyResponseProbability {
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addSeconds := time.Duration(xorshift.Intn(r, h.cfg.MaxIncreaseDelta)+1) * time.Second
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s0, s1 := random.DeriveEntropyFromRequest(req)
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// Generate a probability p < 1.0.
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v, s0, s1 := random.Intn(s0, s1, 1<<24)
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p := float32(v) / (1 << 24)
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if h.cfg.ModifyResponseProbability == 1 || p < h.cfg.ModifyResponseProbability {
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// Generate the increase delta.
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v, _, _ = random.Intn(s0, s1, h.cfg.MaxIncreaseDelta)
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addSeconds := time.Duration(v+1) * time.Second
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resp.Interval += addSeconds
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@ -1,71 +0,0 @@
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// Package xorshift implements the XORShift PRNG.
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package xorshift
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import "sync"
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// XORShift describes the functionality of an XORShift PRNG.
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type XORShift interface {
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Next() uint64
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}
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// XORShift128Plus holds the state of an XORShift128Plus PRNG.
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type XORShift128Plus struct {
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state [2]uint64
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}
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// Next generates a pseudorandom number and advances the state of s.
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func (s *XORShift128Plus) Next() uint64 {
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s1 := s.state[0]
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s0 := s.state[1]
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s1Tmp := s1 // need this for result computation
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s.state[0] = s0
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s1 ^= (s1 << 23) // a
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s.state[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5) // b, c
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return s0 + s1Tmp
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}
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// NewXORShift128Plus creates a new XORShift PRNG.
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func NewXORShift128Plus(s0, s1 uint64) *XORShift128Plus {
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return &XORShift128Plus{
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state: [2]uint64{s0, s1},
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}
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}
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// LockedXORShift128Plus is a thread-safe XORShift128Plus.
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type LockedXORShift128Plus struct {
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sync.Mutex
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state [2]uint64
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}
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// NewLockedXORShift128Plus creates a new LockedXORShift128Plus.
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func NewLockedXORShift128Plus(s0, s1 uint64) *LockedXORShift128Plus {
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return &LockedXORShift128Plus{
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state: [2]uint64{s0, s1},
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}
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}
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// Next generates a pseudorandom number and advances the state of s.
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func (s *LockedXORShift128Plus) Next() uint64 {
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s.Lock()
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s1 := s.state[0]
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s0 := s.state[1]
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s1Tmp := s1 // need this for result computation
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s.state[0] = s0
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s1 ^= (s1 << 23) // a
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s.state[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5) // b, c
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s.Unlock()
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return s0 + s1Tmp
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}
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// Intn generates an int k that satisfies k >= 0 && k < n.
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// n must be > 0.
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func Intn(s XORShift, n int) int {
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if n <= 0 {
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panic("invalid n <= 0")
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}
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v := int(s.Next())
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if v < 0 {
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v = -v
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}
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return v % n
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}
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@ -1,46 +0,0 @@
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package xorshift
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import (
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"math/rand"
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"testing"
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"time"
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"github.com/stretchr/testify/require"
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)
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func TestIntn(t *testing.T) {
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rand.Seed(time.Now().UnixNano())
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s := NewXORShift128Plus(rand.Uint64(), rand.Uint64())
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for i := 0; i < 10000; i++ {
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k := Intn(s, 10)
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require.True(t, k >= 0, "Intn() must be >= 0")
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require.True(t, k < 10, "Intn(k) must be < k")
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}
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}
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func BenchmarkXORShift128Plus_Next(b *testing.B) {
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s := NewXORShift128Plus(rand.Uint64(), rand.Uint64())
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var k uint64
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for i := 0; i < b.N; i++ {
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k = s.Next()
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}
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_ = k
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}
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func BenchmarkIntnXORShift128Plus(b *testing.B) {
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s := NewXORShift128Plus(rand.Uint64(), rand.Uint64())
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var k int
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for i := 0; i < b.N; i++ {
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k = Intn(s, 1000)
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}
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_ = k
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}
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func BenchmarkLockedXORShift128Plus_Next(b *testing.B) {
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s := NewLockedXORShift128Plus(rand.Uint64(), rand.Uint64())
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var k uint64
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for i := 0; i < b.N; i++ {
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k = s.Next()
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}
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_ = k
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}
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