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module sign_extend #(
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parameter WID1 = 18,
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parameter WID2 = 24
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) (
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input [WID1-1:0] b1,
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output [WID2-1:0] b2
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);
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assign b2[WID1-1:0] = b1;
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/* Assign the high bits of b2 to be the extension of the
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* highest bit of b1. If the MSB of b1 is 1 (i.e. b1 is
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* negative), then all high bits of b2 must be negative.
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* If the MSB of b1 is 0, then the high bits of b2 must
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* be zero.
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*/
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assign b2[WID2-1:WID1] = {(WID2-WID1){b1[WID1-1]}};
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endmodule
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