Taken from the Verilog-2001 Language Reference Manual (LRM) standard example since $clog2() doesn't exist prior to Verilog-2005 (and thus, SystemVerilog).
This returns the necessary number of bits to index N items with a binary integer. For example:
Bring in the function at the start of the body of your module like so:
Pass the function a value which, at elaboration time, is either a constant or an expression which evaluates to a constant. Then use that value as an integer for a localparam, genvar, etc...
You don't need this function often, but it's very handy when a module receives some item count as a parameter, and you need to create an internal register to hold an index to those items (e.g.: a binary counter).
function integer clog2; input integer value; begin value = value - 1; for (clog2 = 0; value > 0; clog2 = clog2 + 1) begin value = value >> 1; end end endfunction
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