+ static bool MaybeUri (string s)
+ {
+ int p = s.IndexOf (':');
+ if (p == -1)
+ return false;
+
+ if (p >= 10)
+ return false;
+
+ return IsPredefinedScheme (s.Substring (0, p));
+ }
+
+ //
+ // Using a simple block of if's is twice as slow as the compiler generated
+ // switch statement. But using this tuned code is faster than the
+ // compiler generated code, with a million loops on x86-64:
+ //
+ // With "http": .10 vs .51 (first check)
+ // with "https": .16 vs .51 (second check)
+ // with "foo": .22 vs .31 (never found)
+ // with "mailto": .12 vs .51 (last check)
+ //
+ //
+ static bool IsPredefinedScheme (string scheme)
+ {
+ if (scheme == null || scheme.Length < 3)
+ return false;
+
+ char c = scheme [0];
+ if (c == 'h')
+ return (scheme == "http" || scheme == "https");
+ if (c == 'f')
+ return (scheme == "file" || scheme == "ftp");
+
+ if (c == 'n'){
+ c = scheme [1];
+ if (c == 'e')
+ return (scheme == "news" || scheme == "net.pipe" || scheme == "net.tcp");
+ if (scheme == "nntp")
+ return true;
+ return false;
+ }
+ if ((c == 'g' && scheme == "gopher") || (c == 'm' && scheme == "mailto"))
+ return true;
+
+ return false;
+ }
+