update: added new functionality to SwiftExtensions and HashHelper

Author: mrdav30

src/SwiftCollections/Utilities/HashHelper.cs

@@ -187,5 +187,32 @@ private static uint FMix(uint h)
             h ^= h >> 16;
             return h;
         }
+
+        // System.String.GetHashCode(): http://referencesource.microsoft.com/#mscorlib/system/string.cs,0a17bbac4851d0d4
+        // System.Web.Util.StringUtil.GetStringHashCode(System.String): http://referencesource.microsoft.com/#System.Web/Util/StringUtil.cs,c97063570b4e791a
+        public static int CombineHashCodes(
+            this ITuple tupled,
+            int seed = 5381,
+            int shift1 = 16,
+            int shift2 = 5,
+            int shift3 = 27,
+            int factor3 = 1566083941)
+        {
+            int hash1 = (seed << shift1) + seed;
+            int hash2 = hash1;
+
+            for (int i = 0; i < tupled.Length; i++)
+            {
+                unchecked
+                {
+                    if (i % 2 == 0)
+                        hash1 = ((hash1 << shift2) + hash1 + (hash1 >> shift3)) ^ tupled[i].GetHashCode();
+                    else
+                        hash2 = ((hash2 << shift2) + hash2 + (hash2 >> shift3)) ^ tupled[i].GetHashCode();
+                }
+            }
+
+            return hash1 + (hash2 * factor3);
+        }
     }
 }

src/SwiftCollections/Utilities/SwiftExtensions.cs

@@ -157,5 +157,41 @@ public static bool IsPopulated<T>(this IEnumerable<T> source)
         /// </returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static bool IsPopulatedSafe<T>(this IEnumerable<T> source) => source != null && source.IsPopulated();
+
+        /// <summary>
+        /// Gets the element at the specified index from the end (1-based).
+        /// For example, FromEnd(1) returns the last item, FromEnd(2) returns second-to-last.
+        /// </summary>
+        public static T FromEnd<T>(this IEnumerable<T> source, int reverseIndex)
+        {
+            if (source is SwiftList<T> swift)
+                return swift.FromEnd(reverseIndex);
+
+            // fallback for generic IEnumerable
+            var buffer = new List<T>(source);
+            return buffer.FromEnd(reverseIndex);
+        }
+
+        /// <summary>
+        /// Gets the element at the specified index from the end (1-based) from SwiftList.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static T FromEnd<T>(this SwiftList<T> list, int reverseIndex)
+        {
+            if (reverseIndex <= 0 || reverseIndex > list.Count)
+                throw new ArgumentOutOfRangeException(nameof(reverseIndex));
+            return list[list.Count - reverseIndex];
+        }
+
+        /// <summary>
+        /// Returns the last item in the sequence.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static T Last<T>(this IEnumerable<T> source) => source.FromEnd(1);
+
+        /// <summary>
+        /// Returns the second-to-last item in the sequence.
+        /// </summary>
+        public static T SecondToLast<T>(this IEnumerable<T> source) => source.FromEnd(2);
     }
 }