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+/cmp2lcu.v to work efficiently for fully/partially constant inputs

This commit is contained in:
Eddie Hung 2020-01-20 17:00:35 -08:00
parent 92d70cafec
commit 99a32432aa
1 changed files with 42 additions and 33 deletions
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75
techlibs/common/cmp2lcu.v
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@ -40,67 +40,76 @@ generate
localparam CI = 1'b1;
else
localparam CI = 1'b0;
$__CMP2LCU #(.AB_WIDTH(WIDTH), .AB_SIGNED(A_SIGNED && B_SIGNED), .LCU_WIDTH(0), .BUDGET(`LUT_WIDTH), .CI(CI))
_TECHMAP_REPLACE_ (.A(AA), .B(BB), .P(), .G(), .PP(1'b1), .GG(1'b0), .Y(Y));
$__CMP2LCU #(.AB_WIDTH(WIDTH), .AB_SIGNED(A_SIGNED && B_SIGNED), .LCU_WIDTH(1), .BUDGET(`LUT_WIDTH), .CI(CI))
_TECHMAP_REPLACE_ (.A(AA), .B(BB), .P(1'b1), .G(1'b0), .Y(Y));
end
endgenerate
endmodule
module $__CMP2LCU (A, B, P, G, PP, GG, Y);
module $__CMP2LCU (A, B, P, G, Y);
parameter AB_WIDTH = 0;
parameter AB_SIGNED = 0;
parameter LCU_WIDTH = 0;
parameter LCU_WIDTH = 1;
parameter BUDGET = 0;
parameter CI = 0;
input [AB_WIDTH-1:0] A;
input [AB_WIDTH-1:0] B;
input [LCU_WIDTH-1:0] P;
input [LCU_WIDTH-1:0] G;
input PP;
input GG;
input [AB_WIDTH-1:0] A; // A from original $gt/$ge
input [AB_WIDTH-1:0] B; // B from original $gt/$ge
input [LCU_WIDTH-1:0] P; // P of $lcu
input [LCU_WIDTH-1:0] G; // G of $lcu
output Y;
parameter [AB_WIDTH-1:0] _TECHMAP_CONSTMSK_A_ = 0;
parameter [AB_WIDTH-1:0] _TECHMAP_CONSTMSK_B_ = 0;
parameter [LCU_WIDTH-1:0] _TECHMAP_CONSTMSK_P_ = 0;
generate
if (AB_WIDTH == 0) begin
if (BUDGET < `LUT_WIDTH)
$__CMP2LCU #(.AB_WIDTH(AB_WIDTH), .AB_SIGNED(AB_SIGNED), .LCU_WIDTH(LCU_WIDTH+1), .BUDGET(`LUT_WIDTH), .CI(CI))
_TECHMAP_REPLACE_ (.A(A), .B(B), .P({P, PP}), .G({G, GG}), .PP(1'b1), .GG(1'b0), .Y(Y));
else begin
wire [LCU_WIDTH-1:0] CO;
$lcu #(.WIDTH(LCU_WIDTH)) _TECHMAP_REPLACE_ (.P(P), .G(G), .CI(CI), .CO(CO));
assign Y = CO[LCU_WIDTH-1];
end
wire [LCU_WIDTH-1:0] CO;
$lcu #(.WIDTH(LCU_WIDTH)) _TECHMAP_REPLACE_ (.P(P), .G(G), .CI(CI), .CO(CO));
assign Y = CO[LCU_WIDTH-1];
end
else begin
if (BUDGET < 2)
if (_TECHMAP_CONSTMSK_A_[AB_WIDTH-1:0] && _TECHMAP_CONSTMSK_B_[AB_WIDTH-1:0])
localparam COST = 0;
else if (_TECHMAP_CONSTMSK_A_[AB_WIDTH-1:0] || _TECHMAP_CONSTMSK_B_[AB_WIDTH-1:0])
localparam COST = 1;
else
localparam COST = 2;
if (BUDGET < COST)
$__CMP2LCU #(.AB_WIDTH(AB_WIDTH), .AB_SIGNED(AB_SIGNED), .LCU_WIDTH(LCU_WIDTH+1), .BUDGET(`LUT_WIDTH), .CI(CI))
_TECHMAP_REPLACE_ (.A(A), .B(B), .P({P, PP}), .G({G, GG}), .PP(1'b1), .GG(1'b0), .Y(Y));
_TECHMAP_REPLACE_ (.A(A), .B(B), .P({P, 1'b1}), .G({G, 1'b0}), .Y(Y));
else begin
wire PPP, GGG;
wire PP, GG;
// Bit-wise equality (xnor) of A and B
assign PPP = A[AB_WIDTH-1] ^~ B[AB_WIDTH-1];
assign PP = A[AB_WIDTH-1] ^~ B[AB_WIDTH-1];
if (AB_SIGNED)
assign GGG = ~A[AB_WIDTH-1] & B[AB_WIDTH-1];
else if (BUDGET == `LUT_WIDTH)
assign GGG = A[AB_WIDTH-1] & ~B[AB_WIDTH-1];
assign GG = ~A[AB_WIDTH-1] & B[AB_WIDTH-1];
else if (_TECHMAP_CONSTMSK_P_[LCU_WIDTH-1]) // First compare for LUT if P (and G) is constant
assign GG = A[AB_WIDTH-1] & ~B[AB_WIDTH-1];
else
// Priority "encoder" that checks A[i] == 1'b1 && B[i] == 1'b0
// from MSB down, deferring to less significant bits if the
// MSBs are equal
assign GGG = PP & (A[AB_WIDTH-1] & ~B[AB_WIDTH-1]);
$__CMP2LCU #(.AB_WIDTH(AB_WIDTH-1), .AB_SIGNED(1'b0), .LCU_WIDTH(LCU_WIDTH), .BUDGET(BUDGET-2), .CI(CI))
_TECHMAP_REPLACE_ (.A(A[AB_WIDTH-2:0]), .B(B[AB_WIDTH-2:0]), .P(P), .G(G),
// Propagate only if all bit pairs are equal
assign GG = P[0] & (A[AB_WIDTH-1] & ~B[AB_WIDTH-1]);
if (LCU_WIDTH == 1) begin
// Propagate only if all pairs are equal
// (inconclusive evidence to say A >= B)
.PP(PP & PPP),
// Generate if any bit pairs call for it
.GG(GG | GGG),
.Y(Y));
wire P_ = P[0] & PP;
// Generate if any comparisons call for it
wire G_ = G[0] | GG;
end
else begin
// Propagate only if all pairs are equal
// (inconclusive evidence to say A >= B)
wire [LCU_WIDTH-1:0] P_ = {P[LCU_WIDTH-1:1], P[0] & PP};
// Generate if any comparisons call for it
wire [LCU_WIDTH-1:0] G_ = {G[LCU_WIDTH-1:1], G[0] | GG};
end
$__CMP2LCU #(.AB_WIDTH(AB_WIDTH-1), .AB_SIGNED(1'b0), .LCU_WIDTH(LCU_WIDTH), .BUDGET(BUDGET-COST), .CI(CI))
_TECHMAP_REPLACE_ (.A(A[AB_WIDTH-2:0]), .B(B[AB_WIDTH-2:0]), .P(P_), .G(G_), .Y(Y));
end
end
endgenerate