diff --git a/Parser/XnParser.cs b/Parser/XnParser.cs
index 57c282e..e226488 100644
--- a/Parser/XnParser.cs
+++ b/Parser/XnParser.cs
@@ -35,7 +35,7 @@ namespace XNeedle.Parser
         static Parser<Expression> Function(Context ctx)
         {
             return
-            from name in Parse.Letter.AtLeastOnce().Text()
+            from name in Identifier
             from lparen in Parse.Char('(')
             from expr in Parse.Ref(() => Expr(ctx)).DelimitedBy(Parse.Char(',').Token()).Optional()
             from rparen in Parse.Char(')')
@@ -46,23 +46,44 @@ namespace XNeedle.Parser
         {
             var mathMethodInfo = typeof(Math).GetTypeInfo().GetMethod(name, parameters.Select(e => e.Type).ToArray());
             if (mathMethodInfo != null)
-            {
                 return Expression.Call(mathMethodInfo, parameters);
-            }
-            var ctxMethodInfo = typeof(ContextFunctions).GetTypeInfo().GetMethod(name, parameters.Select(e => e.Type).Prepend(typeof(Context)).ToArray());
+
+            // Find by name and fill in optional parameters with their default values
+            var ctxMethodInfo = typeof(ContextFunctions).GetTypeInfo()
+                .GetMethods()
+                .FirstOrDefault(m =>
+                {
+                    if (m.Name != name) return false;
+                    var mp = m.GetParameters();
+                    if (mp.Length == 0 || mp[0].ParameterType != typeof(Context)) return false;
+                    int required = mp.Skip(1).Count(p => !p.HasDefaultValue);
+                    return parameters.Length >= required && parameters.Length <= mp.Length - 1;
+                });
+
             if (ctxMethodInfo != null)
             {
-                return Expression.Call(ctxMethodInfo, parameters.Prepend(CtxParam).ToArray());
+                var mp = ctxMethodInfo.GetParameters();
+                var args = mp.Skip(1).Select((p, i) =>
+                    i < parameters.Length
+                        ? parameters[i]
+                        : Expression.Constant(p.DefaultValue, p.ParameterType)
+                ).ToArray();
+                return Expression.Call(ctxMethodInfo, args.Prepend(CtxParam).ToArray());
             }
 
             throw new ParseException(string.Format("Function '{0}({1})' does not exist.", name,
                                                         string.Join(",", parameters.Select(e => e.Type.Name))));
         }
 
+        public static readonly Parser<string> HexNumber = 
+            from prefix in Parse.String("0x").Token()
+            from number in Parse.Char(char.IsAsciiHexDigit, "hexadecimal digit").AtLeastOnce().Text()
+            select number;
+
         static readonly Parser<Expression> NumberConstant =
-                Parse.Decimal
-                .Select(x => Expression.Constant(double.Parse(x)))
-                .Named("number");
+            HexNumber.Select(x => Expression.Constant(int.Parse(x, System.Globalization.NumberStyles.HexNumber)))
+            .XOr(Parse.Decimal.Select(x => Expression.Constant(double.Parse(x))))
+            .Named("number");
 
         private static readonly Parser<Expression> StringConstant =
             from open in Parse.Char('"')
@@ -183,10 +204,6 @@ namespace XNeedle.Parser
             from arguments in Argument.DelimitedBy(Parse.Char(',').Token())
             from close in Parse.Char(')')
             select new Call{Identifier = new string(identifier.ToArray()), Arguments = arguments};
-
-        /*public static readonly Parser<Expression> ExpressionObject =
-            from expression in CallObject
-        */
         
         public static CommentParser Comment = new CommentParser { Single = "#", NewLine = Environment.NewLine };
 
diff --git a/Transformation/ContextFunctions.cs b/Transformation/ContextFunctions.cs
index 8bf926d..e2aa770 100644
--- a/Transformation/ContextFunctions.cs
+++ b/Transformation/ContextFunctions.cs
@@ -26,7 +26,41 @@ namespace XNeedle.Transformation
                 level++;
             return level;
         }
-        public static double crc(Context ctx)
+
+        private static uint ComputeCrc32(byte[] data, uint poly, uint init, uint xorOut, bool reflected)
+        {
+            uint crc = init;
+            uint polyReflected = ReflectBits(poly, 32);
+            foreach (byte b in data)
+            {
+                if (reflected)
+                {
+                    crc ^= b;
+                    for (int i = 0; i < 8; i++)
+                        crc = (crc & 1) != 0 ? (crc >> 1) ^ polyReflected : crc >> 1;
+                }
+                else
+                {
+                    crc ^= (uint)b << 24;
+                    for (int i = 0; i < 8; i++)
+                        crc = (crc & 0x80000000u) != 0 ? (crc << 1) ^ poly : crc << 1;
+                }
+            }
+            return crc ^ xorOut;
+        }
+
+        private static uint ReflectBits(uint value, int bits)
+        {
+            uint reflected = 0;
+            for (int i = 0; i < bits; i++)
+            {
+                if ((value & (1u << i)) != 0)
+                    reflected |= 1u << (bits - 1 - i);
+            }
+            return reflected;
+        }
+
+        public static double crc32(Context ctx, int poly = 0x04C11DB7, int init = 0, int xorOut = 0, bool reflected = false)
         {
             if (ctx.Node is null)
                 return 0;
@@ -36,17 +70,15 @@ namespace XNeedle.Transformation
             ctx.Node.WriteTo(writer);
             writer.Flush();
             string xml = buffer.ToString();
-
+            
             // Step 2: Extract all text after the opening tag through and including the closing tag
             string tagName = ctx.Node.Name.LocalName;
             string data = XmlFragParser.ChecksumData(tagName).Parse(xml);
+            //byte[] fragBytes = ctx.SLoc.Encoding.GetBytes(data);
+            byte[] fragBytes = Encoding.UTF8.GetBytes(data);
 
-            // Step 3: Digest into CRC32 using the source encoding
-            var crc32 = new System.IO.Hashing.Crc32();
-            crc32.Append(ctx.SLoc.Encoding.GetBytes(data));
-            uint result = BitConverter.ToUInt32(crc32.GetCurrentHash());
-
-            return (double)result;
+            // Step 3: Digest into CRC32 using parameterized CRC32 - by default MPEG-2
+            return (double)ComputeCrc32(fragBytes, (uint)poly, (uint)init, (uint)xorOut, reflected);
         }
 
         public static string text(Context ctx)