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Multiply using a carry-save accumulator

This commit is contained in:
Clifford Wolf 2014-08-16 21:07:29 +02:00
parent 3b9157f9a6
commit 976bda7102
1 changed files with 45 additions and 5 deletions
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50
techlibs/common/techmap.v
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@ -502,21 +502,61 @@ module \$__arraymul (A, B, Y);
input [WIDTH-1:0] A, B;
output [WIDTH-1:0] Y;
wire [1023:0] _TECHMAP_DO_ = "proc;;";
wire [1023:0] _TECHMAP_DO_ = "proc;; opt";
integer i;
reg [WIDTH-1:0] x, y;
reg [WIDTH-1:0] x;
reg [2*WIDTH-1:0] y;
function [2*WIDTH-1:0] acc_set;
input [WIDTH-1:0] value;
integer k;
begin
for (k = 0; k < WIDTH; k = k+1) begin
acc_set[2*k +: 2] = value[k];
end
end
endfunction
function [2*WIDTH-1:0] acc_add;
input [2*WIDTH-1:0] old_acc;
input [WIDTH-1:0] value;
integer k;
reg a, b, c;
begin
for (k = 0; k < WIDTH; k = k+1) begin
a = old_acc[2*k];
b = k ? old_acc[2*k-1] : 1'b0;
c = value[k];
acc_add[2*k] = (a ^ b) ^ c;
acc_add[2*k+1] = (a & b) | ((a ^ b) & c);
end
end
endfunction
function [WIDTH-1:0] acc_get;
input [2*WIDTH-1:0] acc;
integer k;
begin
// at the end of the multiplier chain the carry-save accumulator
// should also have propagated all carries. thus we just need to
// copy the even bits from the carry accumulator to the output.
for (k = 0; k < WIDTH; k = k+1) begin
acc_get[k] = acc[2*k];
end
end
endfunction
always @* begin
x = B;
y = A[0] ? x : 0;
y = acc_set(A[0] ? x : 0);
for (i = 1; i < WIDTH; i = i+1) begin
x = {x[WIDTH-2:0], 1'b0};
y = y + (A[i] ? x : 0);
y = acc_add(y, A[i] ? x : 0);
end
end
assign Y = y;
assign Y = acc_get(y);
endmodule
module \$mul (A, B, Y);