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 0-bit and the trailing 1’s in the input, producing all 1’s if no 0-bit, and the integer 1 if no trailing 1’s (e.g., 01010111 -> 00001111)
`default_nettype none
module Bitmask_Thermometer_to_Rightmost_0_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