unsafe static string AbsoluteToRelativePath()

in tools/simpleresgen/mono/ResXResourceWriter.cs [356:429]
63 lines of code
16 McCabe index (conditional complexity)

		unsafe static string AbsoluteToRelativePath (string baseDirectoryPath, string absPath)
		{
			if (string.IsNullOrEmpty (baseDirectoryPath))
				return absPath;

			baseDirectoryPath = baseDirectoryPath.TrimEnd (Path.DirectorySeparatorChar);

			fixed (char* bPtr = baseDirectoryPath, aPtr = absPath) {
				var bEnd = bPtr + baseDirectoryPath.Length;
				var aEnd = aPtr + absPath.Length;
				char* lastStartA = aEnd;
				char* lastStartB = bEnd;
				
				int indx = 0;
				// search common base path
				var a = aPtr;
				var b = bPtr;
				while (a < aEnd) {
					if (*a != *b)
						break;
					if (IsSeparator (*a)) {
						indx++;
						lastStartA = a + 1;
						lastStartB = b; 
					}
					a++;
					b++;
					if (b >= bEnd) {
						if (a >= aEnd || IsSeparator (*a)) {
							indx++;
							lastStartA = a + 1;
							lastStartB = b;
						}
						break;
					}
				}
				if (indx == 0) 
					return absPath;
				
				if (lastStartA >= aEnd)
					return ".";
				
				// handle case a: some/path b: some/path/deeper...
				if (a >= aEnd) {
					if (IsSeparator (*b)) {
						lastStartA = a + 1;
						lastStartB = b;
					}
				}
				
				// look how many levels to go up into the base path
				int goUpCount = 0;
				while (lastStartB < bEnd) {
					if (IsSeparator (*lastStartB))
						goUpCount++;
					lastStartB++;
				}
				var size = goUpCount * 2 + goUpCount + aEnd - lastStartA;
				var result = new char [size];
				fixed (char* rPtr = result) {
					// go paths up
					var r = rPtr;
					for (int i = 0; i < goUpCount; i++) {
						*(r++) = '.';
						*(r++) = '.';
						*(r++) = Path.DirectorySeparatorChar;
					}
					// copy the remaining absulute path
					while (lastStartA < aEnd)
						*(r++) = *(lastStartA++);
				}
				return new string (result);
			}
		}