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module shifter (
input [15:0] v, // number to shift
input [15:0] by, // bits to shift by
input dir, // 0 = left shift, 1 = right shift
input [1:0] extend, // 0 = zero extend, 1 = one extend, 2 = sign extend (or last bit), 3 = barrel shift
output [15:0] result
);
wire [31:0] x;
assign x = {
v,
extend == 2'b00 ? 16'h0 :
extend == 2'b01 ? 16'hFFFF :
extend == 2'b10 ? {16{v[dir == 1'b0 ? 0 : 15]}} : v
};
wire [15:0] barrelResult;
wire [15:0] otherResult;
wire [4:0] dirAndAmount;
assign dirAndAmount = {dir, by[3:0]};
assign barrelResult =
|(by[15:4]) ? x[15:0] :
dirAndAmount == 5'h1F ? {x[14:0], x[31 ]} :
dirAndAmount == 5'h1E ? {x[13:0], x[31:30]} :
dirAndAmount == 5'h1D ? {x[12:0], x[31:29]} :
dirAndAmount == 5'h1C ? {x[11:0], x[31:28]} :
dirAndAmount == 5'h1B ? {x[10:0], x[31:27]} :
dirAndAmount == 5'h1A ? {x[ 9:0], x[31:26]} :
dirAndAmount == 5'h19 ? {x[ 8:0], x[31:25]} :
dirAndAmount == 5'h18 ? {x[ 7:0], x[31:24]} :
dirAndAmount == 5'h17 ? {x[ 6:0], x[31:23]} :
dirAndAmount == 5'h16 ? {x[ 5:0], x[31:22]} :
dirAndAmount == 5'h15 ? {x[ 4:0], x[31:21]} :
dirAndAmount == 5'h14 ? {x[ 3:0], x[31:20]} :
dirAndAmount == 5'h13 ? {x[ 2:0], x[31:19]} :
dirAndAmount == 5'h12 ? {x[ 1:0], x[31:18]} :
dirAndAmount == 5'h11 ? {x[ 0], x[31:17]} :
// zero shift is handled at the bottom
dirAndAmount == 5'h01 ? x[30:15] :
dirAndAmount == 5'h02 ? x[29:14] :
dirAndAmount == 5'h03 ? x[28:13] :
dirAndAmount == 5'h04 ? x[27:12] :
dirAndAmount == 5'h05 ? x[26:11] :
dirAndAmount == 5'h06 ? x[25:10] :
dirAndAmount == 5'h07 ? x[24: 9] :
dirAndAmount == 5'h08 ? x[23: 8] :
dirAndAmount == 5'h09 ? x[22: 7] :
dirAndAmount == 5'h0A ? x[21: 6] :
dirAndAmount == 5'h0B ? x[20: 5] :
dirAndAmount == 5'h0C ? x[19: 4] :
dirAndAmount == 5'h0D ? x[18: 3] :
dirAndAmount == 5'h0E ? x[17: 2] :
dirAndAmount == 5'h0F ? x[16: 1] :
x[31:16];
assign otherResult =
|(by[15:4]) ? x[15:0] : barrelResult;
assign result = extend == 2'b11 ? barrelResult : otherResult;
endmodule
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