string persistent hashcode

src/StringExtensions.cs

@@ -39,4 +39,28 @@ public static class StringExtensions
     [Pure]
     public static string RemoveNonDigitOrLetter(this string value) =>
         new(value.Where(char.IsLetterOrDigit).ToArray());
+
+
+    /// <summary>
+    /// Returns a persistent hashcode for the string
+    /// </summary>
+    [Pure]
+    public static int GetStableHashCode(this string str)
+    {
+        unchecked
+        {
+            int hash1 = 5381;
+            int hash2 = hash1;
+
+            for (int i = 0; i < str.Length && str[i] != '\0'; i += 2)
+            {
+                hash1 = ((hash1 << 5) + hash1) ^ str[i];
+                if (i == str.Length - 1 || str[i + 1] == '\0')
+                    break;
+                hash2 = ((hash2 << 5) + hash2) ^ str[i + 1];
+            }
+
+            return hash1 + (hash2 * 1566083941);
+        }
+    }
 }