Remove unsafe from EqualStartingCharacterCount

src/libraries/Common/src/System/IO/PathInternal.cs

@@ -50,30 +50,26 @@ internal static int GetCommonPathLength(string first, string second, bool ignore
         /// <summary>
         /// Gets the count of common characters from the left optionally ignoring case
         /// </summary>
-        internal static unsafe int EqualStartingCharacterCount(string? first, string? second, bool ignoreCase)
+        internal static int EqualStartingCharacterCount(string? first, string? second, bool ignoreCase)
         {
-            if (string.IsNullOrEmpty(first) || string.IsNullOrEmpty(second)) return 0;
-
-            int commonChars = 0;
-
-            fixed (char* f = first)
-            fixed (char* s = second)
+            if (string.IsNullOrEmpty(first) || string.IsNullOrEmpty(second))
             {
-                char* l = f;
-                char* r = s;
-                char* leftEnd = l + first.Length;
-                char* rightEnd = r + second.Length;
+                return 0;
+            }
 
-                while (l != leftEnd && r != rightEnd
-                    && (*l == *r || (ignoreCase && char.ToUpperInvariant(*l) == char.ToUpperInvariant(*r))))
+            int commonLength = first.AsSpan().CommonPrefixLength(second);
+            if (ignoreCase)
+            {
+                for (; (uint)commonLength < (uint)first.Length; commonLength++)
                 {
-                    commonChars++;
-                    l++;
-                    r++;
+                    if (commonLength >= second.Length ||
+                        char.ToUpperInvariant(first[commonLength]) != char.ToUpperInvariant(second[commonLength]))
+                    {
+                        break;
+                    }
                 }
             }
-
-            return commonChars;
+            return commonLength;
         }
 
         /// <summary>