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// Certain arithmetic operations between a signal of width n and a constant can be directly mapped
// to a single k-LUT (where n <= k). This is preferable to normal alumacc techmapping process
// because for many targets, arithmetic techmapping creates hard logic (such as carry cells) which often
// cannot be optimized further.
//
// TODO: Currently, only comparisons with 1-bit output are mapped. Potentially, all arithmetic cells
// with n <= k inputs should be techmapped in this way, because this shortens the critical path
// from n to 1 by avoiding carry chains.
(* techmap_celltype = "$lt $le $gt $ge" *)
module _90_lut_cmp_ (A, B, Y);
parameter A_SIGNED = 0;
parameter B_SIGNED = 0;
parameter A_WIDTH = 0;
parameter B_WIDTH = 0;
parameter Y_WIDTH = 0;
(* force_downto *)
input [A_WIDTH-1:0] A;
(* force_downto *)
input [B_WIDTH-1:0] B;
(* force_downto *)
output [Y_WIDTH-1:0] Y;
parameter _TECHMAP_CELLTYPE_ = "";
parameter _TECHMAP_CONSTMSK_A_ = 0;
parameter _TECHMAP_CONSTVAL_A_ = 0;
parameter _TECHMAP_CONSTMSK_B_ = 0;
parameter _TECHMAP_CONSTVAL_B_ = 0;
function automatic [(1 << `LUT_WIDTH)-1:0] gen_lut;
input integer width;
input integer operation;
input integer swap;
input integer sign;
input integer operand;
integer n, i_var, i_cst, lhs, rhs, o_bit;
begin
gen_lut = width'b0;
for (n = 0; n < (1 << width); n++) begin
if (sign)
i_var = n[width-1:0];
else
i_var = n;
i_cst = operand;
if (swap) begin
lhs = i_cst;
rhs = i_var;
end else begin
lhs = i_var;
rhs = i_cst;
end
if (operation == 0)
o_bit = (lhs < rhs);
if (operation == 1)
o_bit = (lhs <= rhs);
if (operation == 2)
o_bit = (lhs > rhs);
if (operation == 3)
o_bit = (lhs >= rhs);
gen_lut = gen_lut | (o_bit << n);
end
end
endfunction
generate
localparam operation =
_TECHMAP_CELLTYPE_ == "$lt" ? 0 :
_TECHMAP_CELLTYPE_ == "$le" ? 1 :
_TECHMAP_CELLTYPE_ == "$gt" ? 2 :
_TECHMAP_CELLTYPE_ == "$ge" ? 3 :
-1;
if (A_WIDTH > `LUT_WIDTH || B_WIDTH > `LUT_WIDTH || Y_WIDTH != 1)
wire _TECHMAP_FAIL_ = 1;
else if (&_TECHMAP_CONSTMSK_B_)
\$lut #(
.WIDTH(A_WIDTH),
.LUT({ gen_lut(A_WIDTH, operation, 0, A_SIGNED && B_SIGNED, _TECHMAP_CONSTVAL_B_) })
) _TECHMAP_REPLACE_ (
.A(A),
.Y(Y)
);
else if (&_TECHMAP_CONSTMSK_A_)
\$lut #(
.WIDTH(B_WIDTH),
.LUT({ gen_lut(B_WIDTH, operation, 1, A_SIGNED && B_SIGNED, _TECHMAP_CONSTVAL_A_) })
) _TECHMAP_REPLACE_ (
.A(B),
.Y(Y)
);
else
wire _TECHMAP_FAIL_ = 1;
endgenerate
endmodule
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