Simpler int->ip unpacking?

[Vlad Didenko]

I need to get get IPv4 addresses packed in an integer out and do not like the way I end up doing it. Seems to be that too much heavy machinery used for a simple thing. What do I miss?

func int2bytes(ip_int uint64) (net.IP, error) {

var bufarray []byte

buf := bytes.NewBuffer(bufarray)

err = binary.Write(buf, binary.LittleEndian, ip_int)

if err != nil {

return nil, errors.New("Failed to convert integer into bytearray.")

}

return buf.Bytes()[:4], nil

}

Here is the code in the playground...

[peterGo]

Vlad,

    ip_addr = make([]byte, 4)
    binary.LittleEndian.PutUint32(ip_addr, 0x0100007f)

Peter

[Tharaneedharan Vilwanathan]

Hi,

If I am right, this looks simpler and more optimized:

func IntToIP(ip uint64) net.IP {

result := make(net.IP, 4)

        result[0] = byte(ip)

        result[1] = byte(ip >>8)

        result[2] = byte(ip >>16)

        result[3] = byte(ip >> 24)

return result

}

May be there is a better version. Also, please correct me if I am wrong.

Thanks

dharani

On Thu, May 9, 2013 at 10:33 PM, Ryan Leavengood <leave...@gmail.com> wrote:

Replying to myself:

The byte conversion actually makes the masking with & unnecessary. In addition the for can use range. So an even better version is here:

http://play.golang.org/p/Ear5sxnwV9

Regards,

Ryan

On Friday, May 10, 2013 1:03:37 AM UTC-4, Ryan Leavengood wrote:

func intToIP(ip_int uint64) net.IP {

result := make(net.IP, 4)

for i := 0; i < 4; i++ {

result[i] = byte((ip_int >> uint(8 * i)) & 0xff)

}

return result

}

On Friday, May 10, 2013 12:38:54 AM UTC-4, Vlad Didenko wrote:

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[dlin]

I'm wonder do you have the reverse IPToInt()?

[Ryan Leavengood]

Dharani,

Your version looks good, and is indeed quite a bit faster than mine (about 3 times as fast.) I suppose the use of range and the multiply is what is slowing mine so much. Peter's is also very fast (about the same speed as Dharani's) and concise.

In general though they are all so fast in Go that in the grand scheme it probably doesn't matter. A million conversions (leaving out a function call and allocation of the result variable) takes about 6 milliseconds on my machine for both Dharani and Peter's code (and this is with Go 1.0.3.)

I do wonder why this conversion (and the reverse) is not in the standard library.

Regards,

Ryan

[Ryan Leavengood]

To put this topic to bed, the standard library binary.LittleEndian.PutUint32 function which Peter used is exactly Dharani's code:

http://golang.org/src/pkg/encoding/binary/binary.go#L56

So that is what should be used for this. Also since net.IP is really just a byte slice, you can make a variable of that type and use it directly with PutUint32.

Finally the LittleEndian.Uint32 function in the same package above will do the opposite conversion. And again you can just give it a net.IP.

Regards,

Ryan

[Vlad Didenko]

Peter,

Awesome. thank you, that is what I was looking for!

Vlad

[Vlad Didenko]

Ryan,

Absolutely binary package is the way to do it. I did not get type casting right when used shifts in a loop initially, so moved to the binary package. PutUint*  is what I was looking for.

Vlad

[Rémy Oudompheng]

Why did you need to pack IP addresses as integers in the first place?

Rémy.


2013/5/10, Vlad Didenko <busi...@didenko.com>:

> Here is the code in the playground... <http://play.golang.org/p/F-9SDlK-nN>

[Vlad Didenko]

I need to unpack it, because the code I interface with is written by a very clever person and packs it that way.

[slene]

Hi,

Can use this test get almost same speed.

uint32 -> ip string

ip string -> uint32

http://play.golang.org/p/T5B-6RExlj

[李彬]

func inet_aton(ip string) (ip_int uint32) {

ip_byte := net.ParseIP(ip).To4()

for i := 0; i < len(ip_byte); i++ {

ip_int |= uint32(ip_byte[i])

if i < 3 {

ip_int <<= 8

}

}

return

}

func inet_ntoa(ip uint32) string {

return fmt.Sprintf("%d.%d.%d.%d", byte(ip>>24), byte(ip>>16), byte(ip>>8), byte(ip))

}

在 2013年5月10日星期五UTC+8下午12时38分54秒，Vlad Didenko写道：

[chris dollin]

On 12 March 2014 10:27, 李彬 <hdk...@gmail.com> wrote:

func inet_aton(ip string) (ip_int uint32) {

ip_byte := net.ParseIP(ip).To4()

for i := 0; i < len(ip_byte); i++ {

ip_int |= uint32(ip_byte[i])

if i < 3 {

ip_int <<= 8

}

}

return

}

Wouldn't that be simpler as

func inet_aton(ip string) uint32 {
   ip_byte := net.ParseIP(ip).To4()

   return uint32(ip_byte[0] << 24) | uint32(ip_byte[1] << 16) |
        uint32(ip_byte[2] << 8) | uint32(ip_byte[3]);
}

?

Chris

--
Chris "allusive" Dollin