From 9a59c8e07f79b70dd7ec59a2f8ef1ff9572563e6 Mon Sep 17 00:00:00 2001
From: Kevin Kim <kevindkim723@gmail.com>
Date: Thu, 20 Jun 2024 23:46:45 -0700
Subject: [PATCH] reduced bit widths for integer on fpu

---
 config/shared/config-shared.vh       |  8 +++++++-
 config/shared/parameter-defs.vh      |  6 +++++-
 src/cvw.sv                           |  6 ++++++
 src/fpu/fdivsqrt/fdivsqrtpostproc.sv | 20 +++++++++++++-------
 src/fpu/fdivsqrt/fdivsqrtpreproc.sv  |  6 +++---
 5 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/config/shared/config-shared.vh b/config/shared/config-shared.vh
index 44bf77eac..08b8ab739 100644
--- a/config/shared/config-shared.vh
+++ b/config/shared/config-shared.vh
@@ -97,13 +97,19 @@ localparam RK          = LOGR*DIVCOPIES;                            // r*k bits
 localparam FPDIVMINb   = NF + 2; // minimum length of fractional part: Nf result bits + guard and round bits + 1 extra bit to allow sqrt being shifted right
 localparam DIVMINb     = ((FPDIVMINb<XLEN) & IDIV_ON_FPU) ? XLEN : FPDIVMINb; // minimum fractional bits b = max(XLEN, FPDIVMINb)
 localparam RESBITS     = DIVMINb + LOGR; // number of bits in a result: r integer + b fractional
-
+                 
 // division constants
 localparam FPDUR       = (RESBITS-1)/RK + 1 ;                       // ceiling((r+b)/rk)
 localparam DIVb        = FPDUR*RK - LOGR;                           // divsqrt fractional bits, so total number of bits is a multiple of rk after r integer bits
 localparam DURLEN      = $clog2(FPDUR);                             // enough bits to count the duration
 localparam DIVBLEN     = $clog2(DIVb+1);                            // enough bits to count number of fractional bits + 1 integer bit
 
+// integer division/remainder constants
+localparam INTRESBITS     = XLEN + LOGR; // number of bits in a result: r integer + XLEN fractional
+localparam INTFPDUR       = (INTRESBITS-1)/RK + 1 ;                 
+localparam INTDIVb        = INTFPDUR*RK - LOGR;                     
+localparam INTDIVBLEN     = $clog2(INTDIVb+1);        
+
 // largest length in IEU/FPU
 localparam BASECVTLEN = `max(XLEN, NF); // convert length excluding Zfa fcvtmod.w.d
 localparam CVTLEN = (ZFA_SUPPORTED & D_SUPPORTED) ? `max(BASECVTLEN, 32'd84) : BASECVTLEN; // fcvtmod.w.d needs at least 32+52 because a double with 52 fractional bits might be into upper bits of 32 bit word
diff --git a/config/shared/parameter-defs.vh b/config/shared/parameter-defs.vh
index 3dd067b34..cd2a12564 100644
--- a/config/shared/parameter-defs.vh
+++ b/config/shared/parameter-defs.vh
@@ -199,5 +199,9 @@ localparam cvw_t P = '{
   FPDUR       : FPDUR,
   DURLEN      : DURLEN,
   DIVb        : DIVb,
-  DIVBLEN     : DIVBLEN
+  DIVBLEN     : DIVBLEN,
+  INTRESBITS  : INTRESBITS,
+  INTFPDUR    : INTFPDUR,
+  INTDIVb     : INTDIVb,
+  INTDIVBLEN  : INTDIVBLEN
 };
diff --git a/src/cvw.sv b/src/cvw.sv
index a06feb0b9..878f73f57 100644
--- a/src/cvw.sv
+++ b/src/cvw.sv
@@ -294,6 +294,12 @@ typedef struct packed {
   int DURLEN     ;
   int DIVb       ;
   int DIVBLEN    ;
+// integer division/remainder constants
+  int INTRESBITS ;
+  int INTFPDUR   ;
+  int INTDIVb    ;
+  int INTDIVBLEN ;
+  
 } cvw_t;
 
 endpackage
diff --git a/src/fpu/fdivsqrt/fdivsqrtpostproc.sv b/src/fpu/fdivsqrt/fdivsqrtpostproc.sv
index 83eee245a..5e0800b4d 100644
--- a/src/fpu/fdivsqrt/fdivsqrtpostproc.sv
+++ b/src/fpu/fdivsqrt/fdivsqrtpostproc.sv
@@ -97,20 +97,26 @@ module fdivsqrtpostproc import cvw::*;  #(parameter cvw_t P) (
 
   // Integer quotient or remainder correction, normalization, and special cases
   if (P.IDIV_ON_FPU) begin:intpostproc // Int supported
-    logic [P.DIVb+3:0] UnsignedQuotM, NormRemM, NormRemDM, NormQuotM;
-    logic signed [P.DIVb+3:0] PreResultM, PreIntResultM;
+    logic [P.INTDIVb+3:0] UnsignedQuotM, NormRemM, NormRemDM, NormQuotM;
+    logic signed [P.INTDIVb+3:0] PreResultM, PreResultShiftedM, PreIntResultM;
+    logic [P.INTDIVb+3:0] DTrunc, SumTrunc;
+
+
+    assign SumTrunc = Sum[P.DIVb+3:P.DIVb-P.INTDIVb];
+    assign DTrunc = D[P.DIVb+3:P.DIVb-P.INTDIVb];
 
     assign W = $signed(Sum) >>> P.LOGR;
-    assign UnsignedQuotM = {3'b000, PreUmM};
+    assign UnsignedQuotM = {3'b000, PreUmM[P.DIVb:P.DIVb-P.INTDIVb]};
+
 
     // Integer remainder: sticky and sign correction muxes
     assign NegQuotM = AsM ^ BsM; // Integer Quotient is negative
-    mux2 #(P.DIVb+4) normremdmux(W, W+D, NegStickyM, NormRemDM);
-    mux2 #(P.DIVb+4) normremsmux(NormRemDM, -NormRemDM, AsM, NormRemM);
-    mux2 #(P.DIVb+4) quotresmux(UnsignedQuotM, -UnsignedQuotM, NegQuotM, NormQuotM);
+    mux2 #(P.INTDIVb+4) normremdmux(W, W+D, NegStickyM, NormRemDM);
+    mux2 #(P.INTDIVb+4) normremsmux(NormRemDM, -NormRemDM, AsM, NormRemM);
+    mux2 #(P.INTDIVb+4) quotresmux(UnsignedQuotM, -UnsignedQuotM, NegQuotM, NormQuotM);
 
     // Select quotient or remainder and do normalization shift
-    mux2 #(P.DIVb+4)    presresultmux(NormQuotM, NormRemM, RemOpM, PreResultM);
+    mux2 #(P.INTDIVb+4)    presresultmux(NormQuotM, NormRemM, RemOpM, PreResultM);
     assign PreIntResultM = $signed(PreResultM >>> IntNormShiftM); 
 
     // special case logic
diff --git a/src/fpu/fdivsqrt/fdivsqrtpreproc.sv b/src/fpu/fdivsqrt/fdivsqrtpreproc.sv
index 9156005fd..737d9089a 100644
--- a/src/fpu/fdivsqrt/fdivsqrtpreproc.sv
+++ b/src/fpu/fdivsqrt/fdivsqrtpreproc.sv
@@ -119,7 +119,7 @@ module fdivsqrtpreproc import cvw::*;  #(parameter cvw_t P) (
   //////////////////////////////////////////////////////
 
   if (P.IDIV_ON_FPU) begin:intrightshift // Int Supported
-    logic [P.DIVBLEN-1:0] ZeroDiff, p;
+    logic [P.DIVBLEN-1:0] ZeroDiff,p;
 
     // calculate number of fractional bits p
     assign ZeroDiff = mE - ell;         // Difference in number of leading zeros
@@ -218,8 +218,8 @@ module fdivsqrtpreproc import cvw::*;  #(parameter cvw_t P) (
     logic               RemOpE;
 
     /* verilator lint_off WIDTH */
-    assign IntDivNormShiftE = P.DIVb - (CyclesE * P.RK - P.LOGR); // b - rn, used for integer normalization right shift.  n = (Cycles * k - 1)
-    assign IntRemNormShiftE = mE + (P.DIVb-(P.XLEN-1));           // m + b - (N-1) for remainder normalization shift
+    assign IntDivNormShiftE = P.INTDIVb - (CyclesE * P.RK - P.LOGR); // b - rn, used for integer normalization right shift.  n = (Cycles * k - 1)
+    assign IntRemNormShiftE = mE + (P.INTDIVb-(P.XLEN-1));           // m + b - (N-1) for remainder normalization shift
     /* verilator lint_on WIDTH */
     assign RemOpE = Funct3E[1];
     mux2 #(P.DIVBLEN) normshiftmux(IntDivNormShiftE, IntRemNormShiftE, RemOpE, IntNormShiftE);