diff options
Diffstat (limited to 'techlibs/common/mul2dsp.v')
| -rw-r--r-- | techlibs/common/mul2dsp.v | 39 |
1 files changed, 33 insertions, 6 deletions
diff --git a/techlibs/common/mul2dsp.v b/techlibs/common/mul2dsp.v index 75b1242a2..51a6c5fb9 100644 --- a/techlibs/common/mul2dsp.v +++ b/techlibs/common/mul2dsp.v @@ -148,8 +148,17 @@ module _80_mul (A, B, Y); // reduction' approach also exists...
if (i == 0)
assign partial_sum[i] = partial[i];
- else
- assign partial_sum[i] = (partial[i] << i*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)) + partial_sum[i-1];
+ else begin
+ // Rewrite the following statement explicitly in order
+ // to save on a call to 'opt_expr -fine' which would
+ // optimise away the '<<' op and trim size of adder
+ //assign partial_sum[i] = (partial[i] << i*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)) + partial_sum[i-1];
+ wire [Y_WIDTH-1:0] shifted_sum = {partial[i], {i*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom){1'b0}}};
+ assign partial_sum[i] = {
+ partial_sum[i-1][i*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)-1:0],
+ shifted_sum[Y_WIDTH-1:i*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)] + partial_sum[i-1][Y_WIDTH-1:i*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)]
+ };
+ end
end
\$__mul #(
@@ -163,7 +172,12 @@ module _80_mul (A, B, Y); .B(B),
.Y(last_partial)
);
- assign partial_sum[n] = (last_partial << n*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)) + partial_sum[n-1];
+ //assign partial_sum[n] = (last_partial << n*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)) + partial_sum[n-1];
+ wire [Y_WIDTH-1:0] shifted_sum = {last_partial, {n*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom){1'b0}}};
+ assign partial_sum[n] = {
+ partial_sum[n-1][n*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)-1:0],
+ shifted_sum[Y_WIDTH-1:n*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)] + partial_sum[n-1][Y_WIDTH-1:n*(`DSP_A_MAXWIDTH_PARTIAL-sign_headroom)]
+ };
assign Y = partial_sum[n];
end
else if (B_WIDTH > `DSP_B_MAXWIDTH) begin
@@ -199,8 +213,16 @@ module _80_mul (A, B, Y); // reduction' approach also exists...
if (i == 0)
assign partial_sum[i] = partial[i];
- else
- assign partial_sum[i] = (partial[i] << i*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom)) + partial_sum[i-1];
+ else begin
+ // Rewrite the following statement explicitly in order
+ // to save on a call to 'opt_expr -fine' which would
+ // optimise away the '<<' op and trim size of adder
+ wire [Y_WIDTH-1:0] shifted_sum = {partial[i], {i*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom){1'b0}}};
+ assign partial_sum[i] = {
+ partial_sum[i-1][i*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom)-1:0],
+ shifted_sum[Y_WIDTH-1:i*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom)] + partial_sum[i-1][Y_WIDTH-1:i*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom)]
+ };
+ end
end
\$__mul #(
@@ -214,7 +236,12 @@ module _80_mul (A, B, Y); .B(B[B_WIDTH-1 -: last_B_WIDTH]),
.Y(last_partial)
);
- assign partial_sum[n] = (last_partial << n*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom)) + partial_sum[n-1];
+ //assign partial_sum[n] = (last_partial << n*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom)) + partial_sum[n-1];
+ wire [Y_WIDTH-1:0] shifted_sum = {last_partial, {n*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom){1'b0}}};
+ assign partial_sum[n] = {
+ partial_sum[n-1][n*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom)-1:0],
+ shifted_sum[Y_WIDTH-1:n*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom)] + partial_sum[n-1][Y_WIDTH-1:n*(`DSP_B_MAXWIDTH_PARTIAL-sign_headroom)]
+ };
assign Y = partial_sum[n];
end
else begin
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