Reduce linq and use HashCode type

src/Comparation/CollectionEquality.cs

@@ -1,5 +1,4 @@
-using System;
-using System.Collections.Generic;
+using System.Collections.Generic;
 #if NET6_0_OR_GREATER
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
@@ -44,32 +43,10 @@ public bool Equals(IReadOnlyCollection<T?>? x, IReadOnlyCollection<T?>? y)
 
         public int GetHashCode(IReadOnlyCollection<T?> collection)
         {
-            var count = collection.Count;
-#if NETCOREAPP2_1_OR_GREATER
-            var hashCodes = count <= 1024 / sizeof(int)
-                ? stackalloc int[count]
-                : new int[count];
-#else
-            var hashCodes = new int[count];
-#endif
-            var i = 0;
-            foreach (var item in collection)
-            {
-                hashCodes[i++] = itemEquality.GetHashCode(new Box<T?>(item));
-            }
-
-#if NETCOREAPP2_1_OR_GREATER
-            hashCodes.Sort();
-#else
-            Array.Sort(hashCodes);
-#endif
-
             var resultHashCode = 0;
-            foreach (var hashCode in hashCodes)
+            foreach (var item in collection)
             {
-                resultHashCode = unchecked(
-                    (resultHashCode * 397) ^ hashCode
-                );
+                resultHashCode ^= itemEquality.GetHashCode(new Box<T?>(item));
             }
 
             return resultHashCode;

src/Comparation/SequenceEquality.cs

@@ -1,4 +1,7 @@
-using System.Collections.Generic;
+#if !NETSTANDARD2_0
+using System;
+#endif
+using System.Collections.Generic;
 using System.Linq;
 
 namespace Comparation
@@ -29,22 +32,22 @@ public bool Equals(IEnumerable<T?>? x, IEnumerable<T?>? y)
                 return false;
             }
 
-            return x!.SequenceEqual(y!, itemEquality!);
+            return x!.SequenceEqual(y!, itemEquality);
         }
 
         public int GetHashCode(IEnumerable<T?> obj)
         {
-            var hashCode = 0;
+            var hash = new HashCode();
             foreach (var item in obj)
             {
-                var itemHashCode = item is { } value
+                var itemHash = item is { } value
                     ? itemEquality.GetHashCode(value)
                     : 0;
 
-                hashCode = unchecked((hashCode * 397) ^ itemHashCode);
+                hash.Add(itemHash);
             }
 
-            return hashCode;
+            return hash.ToHashCode();
         }
     }
 }