[SOLVED] Radix 4 booth multiplier using 3:2 CSA

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module booth_algorithm (x, y, p);
parameter width=16;
parameter N = width/2;
input[width-1:0]x, y;
output[2*width-1:0]p;
reg [2:0] cc[N-1:0];
reg [width:0] pp[N-1:0];
reg [2*width-1:0] spp[N-1:0];
wire [2*width-1:0] sum8,sum10,sum12,sum14,sum16,sum18,sum20;
wire [2*width-1:0] sum9,sum11,sum13,sum15,sum17,sum19,sum21; 
wire [width:0] inv_x;
integer kk,ii;
assign inv_x = {~x[width-1],~x}+1;
always @ (x or y or inv_x)
begin
cc[0] = {y[1],y[0],1'b0};
for(kk=1;kk<N;kk=kk+1)
cc[kk] = {y[2*kk+1],y[2*kk],y[2*kk-1]};
for(kk=0;kk<N;kk=kk+1)
begin
case(cc[kk])
3'b001 , 3'b010 : pp[kk] = {x[width-1],x};
3'b011 : pp[kk] = {x,1'b0};
3'b100 : pp[kk] = {inv_x[width-1:0],1'b0};
3'b101 , 3'b110 : pp[kk] = inv_x;
default : pp[kk] = 0;
endcase
spp[kk] = $signed(pp[kk]);
end
for(kk=1;kk<N;kk=kk+1)
spp[kk] = {spp[kk],2'b00}; //multiply by 2 to the power x or shifting operation
end
 
//add all partial produces using carry save adders.
//first stage of 3:2 CSA
csa_32 csa_32_0 ( .s1(sum8), .s2(sum9), .p1(spp[0]), .p2(spp[1]), .p3(spp[2]) );
csa_32 csa_32_1 ( .s1(sum10), .s2(sum11), .p1(spp[3]), .p2(spp[4]), .p3(spp[5]) );
csa_32 csa_32_2 ( .s1(sum12), .s2(sum13), .p1(spp[6]), .p2(spp[7]), .p3(32'b0) );
 
////second stage of 3:2 CSA
csa_32 csa_32_3 ( .s1(sum14), .s2(sum15), .p1(sum8), .p2(sum9[31:0]), .p3(sum10) );
csa_32 csa_32_4 ( .s1(sum16), .s2(sum17), .p1(sum11[31:0]), .p2(sum12), .p3(sum13[31:0]) );
 
//third stage of 3:2 CSA
csa_32 csa_32_5 ( .s1(sum18), .s2(sum19), .p1(sum14), .p2(sum15[31:0]), .p3(sum16) );
csa_32 csa_32_6 ( .s1(sum20), .s2(sum21), .p1(sum18), .p2(sum19[31:0]), .p3(sum17[31:0]) );
assign p = sum20+sum21;
endmodule
 
module csa_32(s1,s2,p1,p2,p3);
output [31:0] s1,s2;
input [31:0] p1,p2,p3;
generate
genvar i;
for(i=0;i<32;i=i+1)
begin
assign s1[i]=p1[i]^p2[i]^p3[i];
assign s2[i]=(p1[i]&p2[i]) | (p2[i]&p3[i]) | (p3[i]&p1[i]);
end
endgenerate
endmodule