net: simplify itoa conversions

Rename itod to uitoa to have consistent naming with other itoa functions.
Reduce redundant code by calling uitoa from itoa.
Reduce buffer to maximally needed size for conversion of 64bit integers.
Adjust calls to itoa functions in package net to use new name for itod.
Avoid calls to itoa if uitoa suffices.

Change-Id: I79deaede4d4b0c076a99a4f4dd6f644ba1daec53
Reviewed-on: https://go-review.googlesource.com/2212Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>

src/net/dnsclient.go

@@ -43,8 +43,8 @@ func reverseaddr(addr string) (arpa string, err error) {
 		return "", &DNSError{Err: "unrecognized address", Name: addr}
 	}
 	if ip.To4() != nil {
-		return itoa(int(ip[15])) + "." + itoa(int(ip[14])) + "." + itoa(int(ip[13])) + "." +
-			itoa(int(ip[12])) + ".in-addr.arpa.", nil
+		return uitoa(uint(ip[15])) + "." + uitoa(uint(ip[14])) + "." + uitoa(uint(ip[13])) + "." +
+			uitoa(uint(ip[12])) + ".in-addr.arpa.", nil
 	}
 	// Must be IPv6
 	buf := make([]byte, 0, len(ip)*4+len("ip6.arpa."))

src/net/ip.go

@@ -267,10 +267,10 @@ func (ip IP) String() string {
 
 	// If IPv4, use dotted notation.
 	if p4 := p.To4(); len(p4) == IPv4len {
-		return itod(uint(p4[0])) + "." +
-			itod(uint(p4[1])) + "." +
-			itod(uint(p4[2])) + "." +
-			itod(uint(p4[3]))
+		return uitoa(uint(p4[0])) + "." +
+			uitoa(uint(p4[1])) + "." +
+			uitoa(uint(p4[2])) + "." +
+			uitoa(uint(p4[3]))
 	}
 	if len(p) != IPv6len {
 		return "?"
@@ -491,7 +491,7 @@ func (n *IPNet) String() string {
 	if l == -1 {
 		return nn.String() + "/" + m.String()
 	}
-	return nn.String() + "/" + itod(uint(l))
+	return nn.String() + "/" + uitoa(uint(l))
 }
 
 // Parse IPv4 address (d.d.d.d).

src/net/ipsock.go

@@ -303,7 +303,7 @@ func zoneToString(zone int) string {
 	if ifi, err := InterfaceByIndex(zone); err == nil {
 		return ifi.Name
 	}
-	return itod(uint(zone))
+	return uitoa(uint(zone))
 }
 
 func zoneToInt(zone string) int {

src/net/parse.go

@@ -171,43 +171,30 @@ func xtoi2(s string, e byte) (byte, bool) {
 	return byte(n), ok && ei == 2
 }
 
-// Integer to decimal.
-func itoa(i int) string {
-	var buf [30]byte
-	n := len(buf)
-	neg := false
-	if i < 0 {
-		i = -i
-		neg = true
-	}
-	ui := uint(i)
-	for ui > 0 || n == len(buf) {
-		n--
-		buf[n] = byte('0' + ui%10)
-		ui /= 10
-	}
-	if neg {
-		n--
-		buf[n] = '-'
-	}
-	return string(buf[n:])
+// Convert integer to decimal string.
+func itoa(val int) string {
+	if val < 0 {
+		return "-" + uitoa(uint(-val))
+	}
+	return uitoa(uint(val))
 }
 
-// Convert i to decimal string.
-func itod(i uint) string {
-	if i == 0 {
+// Convert unsigned integer to decimal string.
+func uitoa(val uint) string {
+	if val == 0 { // avoid string allocation
 		return "0"
 	}
-
-	// Assemble decimal in reverse order.
-	var b [32]byte
-	bp := len(b)
-	for ; i > 0; i /= 10 {
-		bp--
-		b[bp] = byte(i%10) + '0'
-	}
-
-	return string(b[bp:])
+	var buf [20]byte // big enough for 64bit value base 10
+	i := len(buf) - 1
+	for val >= 10 {
+		q := val / 10
+		buf[i] = byte('0' + val - q*10)
+		i--
+		val = q
+	}
+	// val < 10
+	buf[i] = byte('0' + val)
+	return string(buf[i:])
 }
 
 // Convert i to a hexadecimal string. Leading zeros are not printed.