Format Hex to Decimal with AMPscript

Question

The FormatNumber function can convert decimal to hex but how do I convert from hex back to decimal? It doesn't work and breaks with error:

An error occurred when attempting to evaluate a FormatNumber function call. The input value (7D29896) cannot be formatted as a number. The first parameter value for a FormatNumber call must be a numeric type supported by the requested format. Value: 7D29896 Format: D

Code:

%%[
@VAR myNum
SET @myNum = 131242134
SET @Hex = FormatNumber(@myNum, "X")
SET @Decimal = FormatNumber(@Hex, "D") /* breaks on this call */
]%%

Original:  %%=v(@myNum)=%%
HEX:  %%=v(@Hex)=%%
DEC:  %%=v(@Decimal)=%%

Answer 1

I don't think there is a built in function in ampscript to achieve that. Anyway, below my SSJS option in case it is useful for you:

<script runat=server>
    Platform.Load("core","1.1.1");

     var myNum = 131242134;
     var Hex = myNum.toString(16);
     var Decimal = parseInt(Hex, 16);

     Write("Original: " + myNum);
     Write("HEX: " + Hex);
     Write("DEC: " + Decimal);
</script>

Answer 2

The problem is where the ??? is. This is not an answer but helps to understand. The problem he is facing is the following: You cannot set a hexadecimal number into a variable that is numeric. If you try to do set @num = FF it won't work. Then if you do set @num = "FF" it is not a numeric type any longer -> you cannot use FormatNumber because it requires a numeric. Even when you cast a variable with formatnumber into a hex numeric, you cannot use this variable to perform hex back to decimal.

 <script runat="server">
        /* Surrounding SSJS try catch block start to get every error that might happen */
        /* Not loading platform core library because of performance aspects */
        Platform.Load("Core", "1.1.5");
        try {
    </script>
%%[
@VAR myNumDec, @myNumHex
SET @myNumDec = 255
SET @Hex = FormatNumber(@myNumDec, "X") 

SET @myNumHex = ???
SET @Dec = FormatNumber(@myNumHex,"D")
]%%
<script runat="server">
     } catch (e) {
        Write("<br>" + Stringify(e));
    }
</script>

OriginalDecimal:  %%=v(@myNumDec)=%%
DecToHex:  %%=v(@Hex)=%%

OriginalHex:  %%=v(@myNumHex)=%%
HexToDEC:  %%=v(@Dec)=%%