Fastest way of converting IPv6 dotted format string to colon format ? C#

Question

What is the fastest way of converting the dotted format of the following IP from version 6 to colon format??

128.91.45.157.220.40.101.10.10.1.252.87.22.200.31.255

I just typed the IP above randomly.

Thanks

Answer 1

var result = new IPAddress(x.Split('.').Select(byte.Parse).ToArray()).ToString();
// result == "805b:2d9d:dc28:650a:a01:fc57:16c8:1fff"

Answer 2

The fastest way would be to do all parsing and conversion yourself.

This is more than ten times faster than the currently accepted answer using Split, Select and IPAddress:

string ip = "128.91.45.157.220.40.101.10.10.1.252.87.22.200.31.255";
StringBuilder b = new StringBuilder(8 * 4 + 7);
string hex = "0123456789abcdef";
int pos = 0;
for (int i = 0; i < 16; i++) {
  int n = 0;
  while (pos < ip.Length && ip[pos] != '.') {
    n = n * 10 + (ip[pos++] - '0');
  }
  pos++;
  b.Append(hex[n / 16]);
  b.Append(hex[n % 16]);
  if (i % 2 == 1 && i < 15) {
    b.Append(':');
  }
}
return b.ToString();

Note: This code does not omit leading zeroes, it always produces a string with eight four-digit values.

Edit:

This is the times per operation that I get from running each a million times:

Fast: 0,00038 ms.
Linq: 0,00689 ms.