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Division cleanup

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This commit is contained in:
David Harris 2023-04-06 21:42:34 -07:00
parent ce931d1fc5
commit c24e81c57f
1 changed files with 37 additions and 29 deletions
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66
src/fpu/fdivsqrt/fdivsqrtpreproc.sv
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@ -54,21 +54,21 @@ module fdivsqrtpreproc (
logic [`DIVb:0] PreSqrtX;
logic [`DIVb+3:0] DivX, DivXShifted, SqrtX, PreShiftX; // Variations of dividend, to be muxed
logic [`NE+1:0] QeE; // Quotient Exponent (FP only)
logic [`DIVb-1:0] IFNormLenX, IFNormLenD; // Correctly-sized inputs for iterator
logic [`DIVb-1:0] IFX, IFD; // Correctly-sized inputs for iterator, selected from int or fp input
logic [`DIVBLEN:0] mE, ell; // Leading zeros of inputs
logic NumerZeroE; // Numerator is zero (X or A)
logic AZeroE, BZeroE; // A or B is Zero for integer division
logic signedDiv; // signed division
logic NegQuotE; // Integer quotient is negative
logic AsE, BsE; // Signs of integer inputs
logic [`XLEN-1:0] AE; // input A after W64 adjustment
if (`IDIV_ON_FPU) begin:intpreproc // Int Supported
logic signedDiv, NegQuotE;
logic AsE, BsE, ALTBE;
logic [`XLEN-1:0] AE, BE, PosA, PosB;
logic [`DIVBLEN:0] ZeroDiff, p;
logic [`XLEN-1:0] BE, PosA, PosB;
// Extract inputs, signs, zero, depending on W64 mode if applicable
assign signedDiv = ~Funct3E[0];
assign NegQuotE = AsE ^ BsE; // Quotient is negative
// Source handling
if (`XLEN==64) begin // 64-bit, supports W64
mux2 #(64) amux(ForwardedSrcAE, {{32{ForwardedSrcAE[31] & signedDiv}}, ForwardedSrcAE[31:0]}, W64E, AE);
@ -81,14 +81,40 @@ module fdivsqrtpreproc (
assign BZeroE = ~(|BE);
assign AsE = AE[`XLEN-1] & signedDiv;
assign BsE = BE[`XLEN-1] & signedDiv;
assign NegQuotE = AsE ^ BsE; // Integer Quotient is negative
// Force integer inputs to be postiive
mux2 #(`XLEN) posamux(AE, -AE, AsE, PosA);
mux2 #(`XLEN) posbmux(BE, -BE, BsE, PosB);
// Select integer or floating point inputs
mux2 #(`DIVb) ifxmux({Xm, {(`DIVb-`NF-1){1'b0}}}, {PosA, {(`DIVb-`XLEN){1'b0}}}, IntDivE, IFNormLenX);
mux2 #(`DIVb) ifdmux({Ym, {(`DIVb-`NF-1){1'b0}}}, {PosB, {(`DIVb-`XLEN){1'b0}}}, IntDivE, IFNormLenD);
mux2 #(`DIVb) ifxmux({Xm, {(`DIVb-`NF-1){1'b0}}}, {PosA, {(`DIVb-`XLEN){1'b0}}}, IntDivE, IFX);
mux2 #(`DIVb) ifdmux({Ym, {(`DIVb-`NF-1){1'b0}}}, {PosB, {(`DIVb-`XLEN){1'b0}}}, IntDivE, IFD);
end else begin // Int not supported
assign IFX = {Xm, {(`DIVb-`NF-1){1'b0}}};
assign IFD = {Ym, {(`DIVb-`NF-1){1'b0}}};
end
// count leading zeros for Subnorm FP and to normalize integer inputs
lzc #(`DIVb) lzcX (IFX, ell);
lzc #(`DIVb) lzcY (IFD, mE);
// Normalization shift
assign XPreproc = IFX << (ell + {{`DIVBLEN{1'b0}}, 1'b1}); // *** try to remove this +1
assign DPreproc = IFD << (mE + {{`DIVBLEN{1'b0}}, 1'b1});
// append leading 1 (for normal inputs)
// shift square root to be in range [1/4, 1)
// Normalized numbers are shifted right by 1 if the exponent is odd
// Denormalized numbers have Xe = 0 and an unbiased exponent of 1-BIAS. They are shifted right if the number of leading zeros is odd.
mux2 #(`DIVb+1) sqrtxmux({~XZeroE, XPreproc}, {1'b0, ~XZeroE, XPreproc[`DIVb-1:1]}, (Xe[0] ^ ell[0]), PreSqrtX);
assign DivX = {3'b000, ~NumerZeroE, XPreproc};
if (`IDIV_ON_FPU) begin:intrightshift // Int Supported
logic [`DIVBLEN:0] ZeroDiff, p;
logic ALTBE;
// calculate number of fractional bits p
assign ZeroDiff = mE - ell; // Difference in number of leading zeros
@ -127,34 +153,16 @@ module fdivsqrtpreproc (
flopen #(1) negquotreg(clk, IFDivStartE, NegQuotE, NegQuotM);
flopen #(1) bzeroreg(clk, IFDivStartE, BZeroE, BZeroM);
flopen #(1) asignreg(clk, IFDivStartE, AsE, AsM);
flopen #(`DIVBLEN+1) nreg(clk, IFDivStartE, nE, nM);
flopen #(`DIVBLEN+1) nreg(clk, IFDivStartE, nE, nM);
flopen #(`DIVBLEN+1) mreg(clk, IFDivStartE, mE, mM);
flopen #(`XLEN) srcareg(clk, IFDivStartE, AE, AM);
if (`XLEN==64)
flopen #(1) w64reg(clk, IFDivStartE, W64E, W64M);
end else begin // Int not supported
assign IFNormLenX = {Xm, {(`DIVb-`NF-1){1'b0}}};
assign IFNormLenD = {Ym, {(`DIVb-`NF-1){1'b0}}};
end else begin
assign NumerZeroE = XZeroE;
assign X = PreShiftX;
end
// count leading zeros for Subnorm FP and to normalize integer inputs
lzc #(`DIVb) lzcX (IFNormLenX, ell);
lzc #(`DIVb) lzcY (IFNormLenD, mE);
// Normalization shift
assign XPreproc = IFNormLenX << (ell + {{`DIVBLEN{1'b0}}, 1'b1}); // *** try to remove this +1
assign DPreproc = IFNormLenD << (mE + {{`DIVBLEN{1'b0}}, 1'b1});
// append leading 1 (for normal inputs)
// shift square root to be in range [1/4, 1)
// Normalized numbers are shifted right by 1 if the exponent is odd
// Denormalized numbers have Xe = 0 and an unbiased exponent of 1-BIAS. They are shifted right if the number of leading zeros is odd.
mux2 #(`DIVb+1) sqrtxmux({~XZeroE, XPreproc}, {1'b0, ~XZeroE, XPreproc[`DIVb-1:1]}, (Xe[0] ^ ell[0]), PreSqrtX);
assign DivX = {3'b000, ~NumerZeroE, XPreproc};
// Sqrt is initialized on step one as R(X-1), so depends on Radix
if (`RADIX == 2) assign SqrtX = {3'b111, PreSqrtX};
else assign SqrtX = {2'b11, PreSqrtX, 1'b0};