Merge pull request #1 from vaskoz/suggestions

Suggestions for performance improvements

main.go

@@ -6,67 +6,53 @@ import (
 	"log"
 	"net"
 	"os"
-	"strconv"
 	"strings"
 	"text/tabwriter"
 )
 
-func inc(ip net.IP) {
-	for j := len(ip) - 1; j >= 0; j-- {
-		ip[j]++
-		if ip[j] > 0 {
-			break
-		}
-	}
-}
-
 func main() {
 	log.SetPrefix("")
 	log.SetFlags(0)
 
 	var ipRange string
-	var err error
 
 	if len(os.Args) > 1 {
 		// The range was passed in as an argument
 		ipRange = os.Args[1]
 	} else {
 		// Read from standard input
 		reader := bufio.NewReader(os.Stdin)
-		ipRange, err = reader.ReadString('\n')
-		if err != nil {
-			log.Fatal(err)
-		}
-		ipRange = strings.TrimSpace(ipRange)
+		ipRange, _ = reader.ReadString('\n')
 	}
 
-	spl := strings.Split(ipRange, "/")
-	if len(spl) < 2 {
-		log.Fatal("bad cidr")
-	}
-	r, err := strconv.Atoi(spl[1])
+	ipRange = strings.TrimSpace(ipRange)
+	addr, network, err := net.ParseCIDR(ipRange)
 	if err != nil {
 		log.Fatal(err)
 	}
-	if r < 8 {
-		log.Fatal("range cannot be smaller than 8")
-	}
 
-	addr, network, err := net.ParseCIDR(ipRange)
-	if err != nil {
-		log.Fatal(err)
+	ipv4 := addr.To4()
+	if ipv4 == nil {
+		log.Fatal("built for IPv4 only")
 	}
 
-	var ips []string
-	for ip := addr.Mask(network.Mask); network.Contains(ip); inc(ip) {
-		ips = append(ips, ip.String())
+	subnetMask := network.Mask
+	firstIp := make([]byte, len(ipv4))
+	lastIp := make([]byte, len(ipv4))
+	numIPs := 0
+
+	for i := range ipv4 {
+		firstIp[i] = ipv4[i] & subnetMask[i]
+		lastIp[i] = ipv4[i] | (subnetMask[i] ^ 0xff)
+		numIPs <<= 8
+		numIPs += int(subnetMask[i] ^ 0xff)
 	}
 
 	w := tabwriter.NewWriter(os.Stdout, 0, 0, 1, ' ', 0)
 	fmt.Fprintf(w, "CIDR Range:\t%s\n", network)
 	fmt.Fprintf(w, "Netmask:\t%d.%d.%d.%d\n", network.Mask[0], network.Mask[1], network.Mask[2], network.Mask[3])
-	fmt.Fprintf(w, "First IP:\t%s\n", ips[0])
-	fmt.Fprintf(w, "Last IP:\t%s\n", ips[len(ips)-1])
-	fmt.Fprintf(w, "Addresses:\t%d\n", len(ips))
+	fmt.Fprintf(w, "First IP:\t%s\n", net.IP(firstIp))
+	fmt.Fprintf(w, "Last IP:\t%s\n", net.IP(lastIp))
+	fmt.Fprintf(w, "Addresses:\t%d\n", numIPs+1)
 	w.Flush()
 }