ipaddr: add Prev, Reset methods to Cursor, IsBroadcast, IsSubnetRoute…

…rAnycast methods to Position

benchmark_test.go

@@ -97,6 +97,26 @@ func BenchmarkCursorNextIPv6(b *testing.B) {
 	}
 }
 
+func BenchmarkCursorPrevIPv4(b *testing.B) {
+	ps := toPrefixes([]string{"192.168.0.255/24"})
+	c := ipaddr.NewCursor(ps)
+
+	for i := 0; i < b.N; i++ {
+		for c.Prev() != nil {
+		}
+	}
+}
+
+func BenchmarkCursorPrevIPv6(b *testing.B) {
+	ps := toPrefixes([]string{"2001:db8::ff/120"})
+	c := ipaddr.NewCursor(ps)
+
+	for i := 0; i < b.N; i++ {
+		for c.Prev() != nil {
+		}
+	}
+}
+
 func BenchmarkPrefixEqualIPv4(b *testing.B) {
 	ps := toPrefixes([]string{"192.168.1.0/24", "192.168.2.0/24"})
 

cursor.go

@@ -9,44 +9,28 @@ import (
 	"net"
 )
 
-// A Position represents a position on a cursor.
-type Position struct {
-	IP     net.IP // IP address
-	Prefix Prefix // IP address prefix
-}
-
-// A Cursor repesents a movable indicator on multiple prefixes.
+// A Cursor repesents a movable indicator on a single or multiple
+// prefixes.
 type Cursor struct {
-	curr, last ipv6Int
+	curr, start, end ipv6Int
 
 	pi int
-	ps []Prefix // IP address prefixes
-}
-
-func (c *Cursor) next() {
-	c.pi++
-	ip := c.ps[c.pi].IP.To16()
-	c.curr = ipToIPv6Int(ip)
-	if ip.To4() != nil {
-		c.last = c.ps[c.pi].lastIPv4MappedInt()
-	}
-	if ip.To16() != nil && ip.To4() == nil {
-		c.last = c.ps[c.pi].lastIPv6Int()
-	}
+	ps []Prefix
 }
 
 func (c *Cursor) set(pi int, ip net.IP) {
 	c.pi = pi
 	c.curr = ipToIPv6Int(ip.To16())
+	c.start = ipToIPv6Int(c.ps[c.pi].IP.To16())
 	if ip.To4() != nil {
-		c.last = c.ps[c.pi].lastIPv4MappedInt()
+		c.end = c.ps[c.pi].lastIPv4MappedIPv6Int()
 	}
 	if ip.To16() != nil && ip.To4() == nil {
-		c.last = c.ps[c.pi].lastIPv6Int()
+		c.end = c.ps[c.pi].lastIPv6Int()
 	}
 }
 
-// First returns the first position on the cursor c.
+// First returns the start position on the cursor c.
 func (c *Cursor) First() *Position {
 	return &Position{IP: c.ps[0].IP, Prefix: c.ps[0]}
 }
@@ -61,15 +45,23 @@ func (c *Cursor) List() []Prefix {
 	return c.ps
 }
 
-// Next returns the next position on the cursor c.
+// Next turns to the next postion on the cursor c.
 // It returns nil at the end on the cursor c.
 func (c *Cursor) Next() *Position {
-	n := c.curr.cmp(&c.last)
+	n := c.curr.cmp(&c.end)
 	if n == 0 {
 		if c.pi == len(c.ps)-1 {
 			return nil
 		}
-		c.next()
+		c.pi++
+		c.curr = ipToIPv6Int(c.ps[c.pi].IP.To16())
+		c.start = c.curr
+		if c.ps[c.pi].IP.To4() != nil {
+			c.end = c.ps[c.pi].lastIPv4MappedIPv6Int()
+		}
+		if c.ps[c.pi].IP.To16() != nil && c.ps[c.pi].IP.To4() == nil {
+			c.end = c.ps[c.pi].lastIPv6Int()
+		}
 	} else {
 		c.curr.incr()
 	}
@@ -81,6 +73,40 @@ func (c *Cursor) Pos() *Position {
 	return &Position{IP: c.curr.ip(), Prefix: c.ps[c.pi]}
 }
 
+// Prev turns to the previous position on the cursor c.
+// It returns nil at the start on the cursor c.
+func (c *Cursor) Prev() *Position {
+	n := c.curr.cmp(&c.start)
+	if n == 0 {
+		if c.pi == 0 {
+			return nil
+		}
+		c.pi--
+		if c.ps[c.pi].IP.To4() != nil {
+			c.curr = c.ps[c.pi].lastIPv4MappedIPv6Int()
+			c.end = c.curr
+		}
+		if c.ps[c.pi].IP.To16() != nil && c.ps[c.pi].IP.To4() == nil {
+			c.curr = c.ps[c.pi].lastIPv6Int()
+			c.end = c.curr
+		}
+		c.start = ipToIPv6Int(c.ps[c.pi].IP.To16())
+	} else {
+		c.curr.decr()
+	}
+	return c.Pos()
+}
+
+// Reset resets all state and switches the prefixes to ps.
+// It uses the existing prefixes when ps is nil.
+func (c *Cursor) Reset(ps []Prefix) {
+	ps = sortAndDedup(ps, false)
+	if len(ps) > 0 {
+		c.ps = ps
+	}
+	c.set(0, c.ps[0].IP.To16())
+}
+
 // Set sets the current postion on the cursor c to pos.
 func (c *Cursor) Set(pos *Position) error {
 	if pos == nil {
@@ -102,9 +128,6 @@ func (c *Cursor) Set(pos *Position) error {
 
 // NewCursor returns a new cursor.
 func NewCursor(ps []Prefix) *Cursor {
-	if len(ps) == 0 {
-		return nil
-	}
 	ps = sortAndDedup(ps, false)
 	if len(ps) == 0 {
 		return nil