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lza cleanup

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This commit is contained in:
David Harris 2022-08-01 15:37:09 -07:00
parent 31215277ee
commit 4953ccf273
2 changed files with 9 additions and 7 deletions
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3
pipelined/src/fpu/fma.sv
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@ -85,6 +85,7 @@ module fma(
fmaadd add(.Am, .Pm, .Ze, .Pe, .Ps, .As, .KillProd, .ZmSticky, .AmInv, .PmKilled, .NegSum, .InvA, .Sm, .Se, .Ss);
fmalza lza(.A(AmInv), .Pm({PmKilled, 1'b0, InvA&Ps&ZmSticky&KillProd}), .Cin(InvA & ~(ZmSticky & ~KillProd)), .SCnt);
fmalza lza(.A(AmInv), .Pm({PmKilled, 1'b0, InvA&Ps&ZmSticky&KillProd}), .Cin(InvA & ~(ZmSticky & ~KillProd)), .sub(InvA), .SCnt);
endmodule

13
pipelined/src/fpu/fmalza.sv
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@ -32,26 +32,27 @@
module fmalza( // [Schmookler & Nowka, Leading zero anticipation and detection, IEEE Sym. Computer Arithmetic, 2001]
input logic [3*`NF+6:0] A, // addend
input logic [2*`NF+3:0] Pm, // product
input logic Cin, // carry in
input logic Cin, // carry in
input logic sub,
output logic [$clog2(3*`NF+7)-1:0] SCnt // normalization shift count for the positive result
);
localparam WIDTH = 3*`NF+7;
logic [WIDTH-1:0] B,F;
logic [WIDTH-1:0] P, G;
logic [WIDTH-2:0] K;
logic [WIDTH-2:0] P, G, K;
logic [WIDTH-2:0] Pp1, Gm1, Km1;
assign B = {{(`NF+3){1'b0}}, Pm}; // Zero extend product
// next steps***replace P[WIDTH-1] with sub, then remove one bit from A
assign P = A^B;
assign P = A[WIDTH-2:0]^B[WIDTH-2:0];
assign G = A[WIDTH-2:0]&B[WIDTH-2:0];
assign K= ~A[WIDTH-2:0]&~B[WIDTH-2:0];
assign Pp1 = {A[WIDTH-1], P[WIDTH-2:1]};
assign Pp1 = {sub, P[WIDTH-2:1]};
// assign Pp1 = {A[WIDTH-1], P[WIDTH-2:1]};
assign Gm1 = {G[WIDTH-3:0], Cin};
assign Km1 = {K[WIDTH-3:0], ~Cin};
@ -59,7 +60,7 @@ module fmalza( // [Schmookler & Nowka, Leading zero anticipation and detection,
// - note: the paper linked above uses the numbering system where 0 is the most significant bit
//f[n] = ~P[n]&P[n-1] note: n is the MSB
//f[i] = (P[i+1]&(G[i]&~K[i-1] | K[i]&~G[i-1])) | (~P[i+1]&(K[i]&~K[i-1] | G[i]&~G[i-1]))
assign F[WIDTH-1] = ~P[WIDTH-1]&P[WIDTH-2];
assign F[WIDTH-1] = ~sub&P[WIDTH-2];
assign F[WIDTH-2:0] = (Pp1&(G&~Km1 | K&~Gm1)) | (~Pp1&(K&~Km1 | G&~Gm1));
lzc #(WIDTH) lzc (.num(F), .ZeroCnt(SCnt));