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He means I think modulo (2*w).
For this term:
mod 2 w if w is a constant then you can directly implement your function in vhdl and it will be synthethisabe. (X (2X+1)) is simple to translate in synthetizable VHDL.
If you have w as a varialble it would not be the case and you can use the technique provided here: https://www.edaboard.com/viewtopic.php?t=118547&highlight=modulo