net/packet: represent IP6 as two uint64s.

For the operations we perform on these types (mostly net6.Contains),
this encoding is much faster.

Part of #19.

name                   old time/op    new time/op    delta
Filter/icmp4-8           27.5ns ± 1%    28.0ns ± 2%   +1.89%  (p=0.016 n=5+5)
Filter/tcp4_syn_in-8     38.8ns ± 2%    38.3ns ± 1%   -1.24%  (p=0.024 n=5+5)
Filter/tcp4_syn_out-8    27.6ns ±12%    24.6ns ± 1%     ~     (p=0.063 n=5+5)
Filter/udp4_in-8         71.5ns ± 5%    65.9ns ± 1%   -7.94%  (p=0.008 n=5+5)
Filter/udp4_out-8         132ns ±13%     119ns ± 1%  -10.29%  (p=0.008 n=5+5)
Filter/icmp6-8            169ns ±10%      54ns ± 1%  -68.35%  (p=0.008 n=5+5)
Filter/tcp6_syn_in-8      149ns ± 6%      43ns ± 1%  -71.11%  (p=0.008 n=5+5)
Filter/tcp6_syn_out-8    37.7ns ± 4%    24.3ns ± 3%  -35.51%  (p=0.008 n=5+5)
Filter/udp6_in-8          179ns ± 5%     103ns ± 1%  -42.75%  (p=0.008 n=5+5)
Filter/udp6_out-8         156ns ± 3%     191ns ± 1%  +22.54%  (p=0.008 n=5+5)

Signed-off-by: David Anderson <danderson@tailscale.com>

net/packet/ip6.go

@@ -12,19 +12,25 @@ import (
 )
 
 // IP6 is an IPv6 address.
-type IP6 [16]byte // TODO: maybe 2x uint64 would be faster for the type of ops we do?
+type IP6 struct {
+	Hi, Lo uint64
+}
 
 // IP6FromNetaddr converts a netaddr.IP to an IP6. Panics if !ip.Is6.
 func IP6FromNetaddr(ip netaddr.IP) IP6 {
 	if !ip.Is6() {
 		panic(fmt.Sprintf("IP6FromNetaddr called with non-v6 addr %q", ip))
 	}
-	return IP6(ip.As16())
+	b := ip.As16()
+	return IP6{binary.BigEndian.Uint64(b[:8]), binary.BigEndian.Uint64(b[8:])}
 }
 
 // Netaddr converts ip to a netaddr.IP.
 func (ip IP6) Netaddr() netaddr.IP {
-	return netaddr.IPFrom16(ip)
+	var b [16]byte
+	binary.BigEndian.PutUint64(b[:8], ip.Hi)
+	binary.BigEndian.PutUint64(b[8:], ip.Lo)
+	return netaddr.IPFrom16(b)
 }
 
 func (ip IP6) String() string {
@@ -32,11 +38,11 @@ func (ip IP6) String() string {
 }
 
 func (ip IP6) IsMulticast() bool {
-	return ip[0] == 0xFF
+	return (ip.Hi >> 56) == 0xFF
 }
 
 func (ip IP6) IsLinkLocalUnicast() bool {
-	return ip[0] == 0xFE && ip[1] == 0x80
+	return (ip.Hi >> 48) == 0xFE80
 }
 
 // ip6HeaderLength is the length of an IPv6 header with no IP options.
@@ -69,8 +75,10 @@ func (h IP6Header) Marshal(buf []byte) error {
 	binary.BigEndian.PutUint16(buf[4:6], uint16(len(buf)-ip6HeaderLength)) // Total length
 	buf[6] = uint8(h.IPProto)                                              // Inner protocol
 	buf[7] = 64                                                            // TTL
-	copy(buf[8:24], h.SrcIP[:])
-	copy(buf[24:40], h.DstIP[:])
+	binary.BigEndian.PutUint64(buf[8:16], h.SrcIP.Hi)
+	binary.BigEndian.PutUint64(buf[16:24], h.SrcIP.Lo)
+	binary.BigEndian.PutUint64(buf[24:32], h.DstIP.Hi)
+	binary.BigEndian.PutUint64(buf[32:40], h.DstIP.Lo)
 
 	return nil
 }
@@ -92,8 +100,10 @@ func (h IP6Header) marshalPseudo(buf []byte) error {
 		return errLargePacket
 	}
 
-	copy(buf[:16], h.SrcIP[:])
-	copy(buf[16:32], h.DstIP[:])
+	binary.BigEndian.PutUint64(buf[:8], h.SrcIP.Hi)
+	binary.BigEndian.PutUint64(buf[8:16], h.SrcIP.Lo)
+	binary.BigEndian.PutUint64(buf[16:24], h.DstIP.Hi)
+	binary.BigEndian.PutUint64(buf[24:32], h.DstIP.Lo)
 	binary.BigEndian.PutUint32(buf[32:36], uint32(len(buf)-h.Len()))
 	buf[36] = 0
 	buf[37] = 0

net/packet/packet.go

@@ -248,8 +248,10 @@ func (q *Parsed) decode6(b []byte) {
 		return
 	}
 
-	copy(q.SrcIP6[:], b[8:24])
-	copy(q.DstIP6[:], b[24:40])
+	q.SrcIP6.Hi = binary.BigEndian.Uint64(b[8:16])
+	q.SrcIP6.Lo = binary.BigEndian.Uint64(b[16:24])
+	q.DstIP6.Hi = binary.BigEndian.Uint64(b[24:32])
+	q.DstIP6.Lo = binary.BigEndian.Uint64(b[32:40])
 
 	// We don't support any IPv6 extension headers. Don't try to
 	// be clever. Therefore, the IP subprotocol always starts at

wgengine/filter/match6.go

@@ -6,6 +6,7 @@ package filter
 
 import (
 	"fmt"
+	"math/bits"
 	"strings"
 
 	"inet.af/netaddr"
@@ -14,16 +15,24 @@ import (
 
 type net6 struct {
 	ip   packet.IP6
-	bits uint8
+	mask packet.IP6
 }
 
 func net6FromIPPrefix(pfx netaddr.IPPrefix) net6 {
 	if !pfx.IP.Is6() {
 		panic("net6FromIPPrefix given non-ipv6 prefix")
 	}
+	var mask packet.IP6
+	if pfx.Bits > 64 {
+		mask.Hi = ^uint64(0)
+		mask.Lo = (^uint64(0) << (128 - pfx.Bits))
+	} else {
+		mask.Hi = (^uint64(0) << (64 - pfx.Bits))
+	}
+
 	return net6{
 		ip:   packet.IP6FromNetaddr(pfx.IP),
-		bits: pfx.Bits,
+		mask: mask,
 	}
 }
 
@@ -37,33 +46,22 @@ func nets6FromIPPrefixes(pfxs []netaddr.IPPrefix) (ret []net6) {
 }
 
 func (n net6) Contains(ip packet.IP6) bool {
-	// Implementation stolen from inet.af/netaddr
-	bits := n.bits
-	for i := 0; bits > 0 && i < len(n.ip); i++ {
-		m := uint8(255)
-		if bits < 8 {
-			zeros := 8 - bits
-			m = m >> zeros << zeros
-		}
-		if n.ip[i]&m != ip[i]&m {
-			return false
-		}
-		if bits < 8 {
-			break
-		}
-		bits -= 8
-	}
-	return true
+	return ((n.ip.Hi&n.mask.Hi) == (ip.Hi&n.mask.Hi) &&
+		(n.ip.Lo&n.mask.Lo) == (ip.Lo&n.mask.Lo))
+}
+
+func (n net6) Bits() int {
+	return 128 - bits.TrailingZeros64(n.mask.Hi) - bits.TrailingZeros64(n.mask.Lo)
 }
 
 func (n net6) String() string {
-	switch n.bits {
+	switch n.Bits() {
 	case 128:
 		return n.ip.String()
 	case 0:
 		return "*"
 	default:
-		return fmt.Sprintf("%s/%d", n.ip, n.bits)
+		return fmt.Sprintf("%s/%d", n.ip, n.Bits())
 	}
 }