Credit: Hacker's Delight, Section 2-1: Manipulating Rightmost Bits
Use the following formula to create a word with 1’s at the positions of the rightmost 1-bit and the trailing 0’s in the input, producing all 1’s if no 1-bit, and the integer 1 if no trailing 0’s (e.g., 01011000 -> 00001111)
`default_nettype none module Bitmask_Thermometer_to_Rightmost_1_Bit #( parameter WORD_WIDTH = 0 ) ( input wire [WORD_WIDTH-1:0] word_in, output reg [WORD_WIDTH-1:0] word_out ); initial begin word_out = {WORD_WIDTH{1'b0}}; end localparam ONE = {{WORD_WIDTH-1{1'b0}},1'b1}; always @(*) begin word_out = word_in ^ (word_in - ONE); end endmodule