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Cleaning shifter

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This commit is contained in:
David Harris 2021-12-18 09:43:09 -08:00
parent ebcffcdebd
commit 53baf3e787
1 changed files with 3 additions and 8 deletions
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11
wally-pipelined/src/ieu/shifter.sv
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@ -38,7 +38,7 @@ module shifter (
// extension.
generate
if (`XLEN==32) begin
if (`XLEN==32) begin:shifter
// funnel shifter (see CMOS VLSI Design 4e Section 11.8.1, note Table 11.11 shift types wrong)
logic [62:0] z, zshift;
logic [4:0] offset;
@ -56,7 +56,7 @@ module shifter (
// funnel operation
assign zshift = z >> offset;
assign y = zshift[31:0];
end else begin // RV64
end else begin:shifter // RV64
// funnel shifter followed by masking
// research idea: investigate shifter designs for mixed 32/64-bit shifts
logic [126:0] z, zshift;
@ -83,12 +83,7 @@ module shifter (
// funnel operation
assign zshift = z >> offset;
assign ylower = zshift[31:0];
// mask upper 32 bits for W-type 32-bit shifts
// harris: is there a clever way to get zshift[31] earlier for arithmetic right shifts to speed up critical path?
assign yupper = w64 ? {32{zshift[31]}} : zshift[63:32];
assign y = {yupper, ylower};
assign y = zshift[63:0];
end
endgenerate
endmodule