Replaced recursive lcu scheme with bk adder

diff --git a/techlibs/common/techmap.v b/techlibs/common/techmap.v
index 9bdff4f336d274bd71e40b40538b14d27ff0ec77..5bbe883ef41df9be5615f2bfa081589df0fe08a1 100644 (file)
--- a/techlibs/common/techmap.v
+++ b/techlibs/common/techmap.v
@@ -285,80 +285,50 @@ module \$__alu_ripple (A, B, CI, X, Y, CO, CS);
        endgenerate
 endmodule
 
-module \$__lcu_simple (P, G, CI, CO, PG, GG);
-       parameter WIDTH = 1;
+module \$__lcu (P, G, CI, CO);
+       parameter WIDTH = 2;
 
        input [WIDTH-1:0] P, G;
        input CI;
 
        output reg [WIDTH:0] CO;
-       output reg PG, GG;
 
-       wire [1023:0] _TECHMAP_DO_ = "proc;;";
+       integer i, j, k;
+       reg [WIDTH-1:0] p, g;
 
-       integer i, j;
-       reg [WIDTH-1:0] tmp;
+       wire [1023:0] _TECHMAP_DO_ = "proc; opt -fast";
 
        always @* begin
-               PG = &P;
-               GG = 0;
-               for (i = 0; i < WIDTH; i = i+1) begin
-                       tmp = ~0;
-                       tmp[i] = G[i];
-                       for (j = i+1; j < WIDTH; j = j+1)
-                               tmp[j] = P[j];
-                       GG = GG || &tmp[WIDTH-1:i];
-               end
-
-               CO[0] = CI;
-               for (i = 0; i < WIDTH; i = i+1)
-                       CO[i+1] = G[i] | (P[i] & CO[i]);
-       end
-endmodule
-
-module \$__lcu (P, G, CI, CO, PG, GG);
-       parameter WIDTH = 1;
-
-       function integer get_group_size;
-               begin
-                       get_group_size = 4;
-                       while (4 * get_group_size < WIDTH)
-                               get_group_size = 4 * get_group_size;
+               p = P;
+               g = G;
+
+               // in almost all cases CI will be constant zero
+               g[0] = g[0] | (p[0] & CI);
+
+               // [[CITE]] Brent Kung Adder
+               // R. P. Brent and H. T. Kung, “A Regular Layout for Parallel Adders”,
+               // IEEE Transaction on Computers, Vol. C-31, No. 3, p. 260-264, March, 1982
+
+               // Main tree
+               for (i = 1; i <= $clog2(WIDTH); i = i+1) begin
+                       for (j = 2**i - 1; j < WIDTH; j = j + 2**i) begin
+                               k = j - 2**(i-1);
+                               g[j] = g[j] | p[j] & g[k];
+                               p[j] = p[j] & p[k];
+                       end
                end
-       endfunction
 
-       input [WIDTH-1:0] P, G;
-       input CI;
-
-       output [WIDTH:0] CO;
-       output PG, GG;
-
-       genvar i;
-       generate
-               if (WIDTH <= 4) begin
-                       \$__lcu_simple #(.WIDTH(WIDTH)) _TECHMAP_REPLACE_ (.P(P), .G(G), .CI(CI), .CO(CO), .PG(PG), .GG(GG));
-               end else begin
-                       localparam GROUP_SIZE = get_group_size();
-                       localparam GROUPS_NUM = (WIDTH + GROUP_SIZE - 1) / GROUP_SIZE;
-
-                       wire [GROUPS_NUM-1:0] groups_p, groups_g;
-                       wire [GROUPS_NUM:0] groups_ci;
-
-                       for (i = 0; i < GROUPS_NUM; i = i+1) begin:V
-                               localparam g_size = `MIN(GROUP_SIZE, WIDTH - i*GROUP_SIZE);
-                               localparam g_offset = i*GROUP_SIZE;
-                               wire [g_size:0] g_co;
-
-                               \$__lcu #(.WIDTH(g_size)) g (.P(P[g_offset +: g_size]), .G(G[g_offset +: g_size]),
-                                               .CI(groups_ci[i]), .CO(g_co), .PG(groups_p[i]), .GG(groups_g[i]));
-                               assign CO[g_offset+1 +: g_size] = g_co[1 +: g_size];
+               // Inverse tree
+               for (i = $clog2(WIDTH); i > 0; i = i-1) begin
+                       for (j = 2**i + 2**(i-1) - 1; j < WIDTH; j = j + 2**i) begin
+                               k = j - 2**(i-1);
+                               g[j] = g[j] | p[j] & g[k];
+                               p[j] = p[j] & p[k];
                        end
-
-                       \$__lcu_simple #(.WIDTH(GROUPS_NUM)) super_lcu (.P(groups_p), .G(groups_g), .CI(CI), .CO(groups_ci), .PG(PG), .GG(GG));
-
-                       assign CO[0] = CI;
                end
-       endgenerate
+       end
+
+       assign CO = {g, CI};
 endmodule
 
 module \$__alu_lookahead (A, B, CI, X, Y, CO, CS);