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Bitmask_0_Bit_at_Rightmost_1_Bit.html
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<html>
<head>
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<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="description" content="Credit: [Hacker's Delight](./reading.html#Warren2013), Section 2-1: Manipulating Rightmost Bits">
<title>Bitmask 0 Bit at Rightmost 1 Bit</title>
</head>
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<h1>Bitmask: 0 Bit at Rightmost 1 Bit</h1>
<p>Credit: <a href="./reading.html#Warren2013">Hacker's Delight</a>, Section 2-1: Manipulating Rightmost Bits</p>
<p>Use the following formula to create a word with a single 0-bit at the
position of the rightmost 1-bit in the input, producing all 1’s if none
(e.g., 10101000 -> 11110111)</p>
<pre>
`default_nettype none
module <a href="./Bitmask_0_Bit_at_Rightmost_1_Bit.html">Bitmask_0_Bit_at_Rightmost_1_Bit</a>
#(
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
</pre>
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