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diff --git a/src/mscorlib/shared/System/IO/PathInternal.Windows.StringBuffer.cs b/src/mscorlib/shared/System/IO/PathInternal.Windows.StringBuffer.cs
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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+
+namespace System.IO
+{
+ /// <summary>Contains internal path helpers that are shared between many projects.</summary>
+ internal static partial class PathInternal
+ {
+ /// <summary>
+ /// Returns true if the path uses the extended syntax (\\?\)
+ /// </summary>
+ internal static bool IsExtended(ref StringBuffer path)
+ {
+ // While paths like "//?/C:/" will work, they're treated the same as "\\.\" paths.
+ // Skipping of normalization will *only* occur if back slashes ('\') are used.
+ return path.Length >= DevicePrefixLength
+ && path[0] == '\\'
+ && (path[1] == '\\' || path[1] == '?')
+ && path[2] == '?'
+ && path[3] == '\\';
+ }
+
+ /// <summary>
+ /// Gets the length of the root of the path (drive, share, etc.).
+ /// </summary>
+ internal unsafe static int GetRootLength(ref StringBuffer path)
+ {
+ if (path.Length == 0) return 0;
+
+ fixed (char* value = path.UnderlyingArray)
+ {
+ return GetRootLength(value, path.Length);
+ }
+ }
+
+ /// <summary>
+ /// Returns true if the path uses any of the DOS device path syntaxes. ("\\.\", "\\?\", or "\??\")
+ /// </summary>
+ internal static bool IsDevice(ref StringBuffer path)
+ {
+ // If the path begins with any two separators is will be recognized and normalized and prepped with
+ // "\??\" for internal usage correctly. "\??\" is recognized and handled, "/??/" is not.
+ return IsExtended(ref path)
+ ||
+ (
+ path.Length >= DevicePrefixLength
+ && IsDirectorySeparator(path[0])
+ && IsDirectorySeparator(path[1])
+ && (path[2] == '.' || path[2] == '?')
+ && IsDirectorySeparator(path[3])
+ );
+ }
+
+ /// <summary>
+ /// Returns true if the path specified is relative to the current drive or working directory.
+ /// Returns false if the path is fixed to a specific drive or UNC path. This method does no
+ /// validation of the path (URIs will be returned as relative as a result).
+ /// </summary>
+ /// <remarks>
+ /// Handles paths that use the alternate directory separator. It is a frequent mistake to
+ /// assume that rooted paths (Path.IsPathRooted) are not relative. This isn't the case.
+ /// "C:a" is drive relative- meaning that it will be resolved against the current directory
+ /// for C: (rooted, but relative). "C:\a" is rooted and not relative (the current directory
+ /// will not be used to modify the path).
+ /// </remarks>
+ internal static bool IsPartiallyQualified(ref StringBuffer path)
+ {
+ if (path.Length < 2)
+ {
+ // It isn't fixed, it must be relative. There is no way to specify a fixed
+ // path with one character (or less).
+ return true;
+ }
+
+ if (IsDirectorySeparator(path[0]))
+ {
+ // There is no valid way to specify a relative path with two initial slashes or
+ // \? as ? isn't valid for drive relative paths and \??\ is equivalent to \\?\
+ return !(path[1] == '?' || IsDirectorySeparator(path[1]));
+ }
+
+ // The only way to specify a fixed path that doesn't begin with two slashes
+ // is the drive, colon, slash format- i.e. C:\
+ return !((path.Length >= 3)
+ && (path[1] == VolumeSeparatorChar)
+ && IsDirectorySeparator(path[2]));
+ }
+ }
+}