From a85a868b5627b48ac95dffb33bbdbafdcb6652cd Mon Sep 17 00:00:00 2001
From: Katherine Parry <kparry4@gmail.com>
Date: Fri, 24 Jun 2022 21:02:50 +0000
Subject: [PATCH] radix 4 division denormal result handeling

---
 pipelined/src/fpu/divshiftcalc.sv | 14 +++++++++++---
 pipelined/src/fpu/postprocess.sv  |  5 +++--
 pipelined/srt/srt-radix4.sv       |  2 +-
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/pipelined/src/fpu/divshiftcalc.sv b/pipelined/src/fpu/divshiftcalc.sv
index 398e8f467..d1a364b3c 100644
--- a/pipelined/src/fpu/divshiftcalc.sv
+++ b/pipelined/src/fpu/divshiftcalc.sv
@@ -4,12 +4,20 @@ module divshiftcalc(
     input logic  [`DIVLEN+2:0] Quot,
     input logic  [`NE+1:0] DivCalcExpM,
     output logic [$clog2(`NORMSHIFTSZ)-1:0] DivShiftAmt,
+    output logic [`NORMSHIFTSZ-1:0] DivShiftIn,
     output logic [`NE+1:0] CorrDivExp
 );
-    
-    assign DivShiftAmt = {{$clog2(`NORMSHIFTSZ)-1{1'b0}}, ~Quot[`DIVLEN+2]};
+    logic ResDenorm;
+    logic [`NE+1:0] DenormShift;
+    logic [`NE+1:0] NormShift;
+    assign ResDenorm = DivCalcExpM[`NE+1];
+    assign DenormShift = (`NE+2)'(`NF-1)+DivCalcExpM;
+    assign NormShift = {(`NE+1)'(0), ~Quot[`DIVLEN+2]} + (`NE+2)'(`NF);
+    assign DivShiftAmt = ResDenorm ?  DenormShift[$clog2(`NORMSHIFTSZ)-1:0] : NormShift[$clog2(`NORMSHIFTSZ)-1:0];
+
+    assign DivShiftIn = {(`NF)'(0), Quot[`DIVLEN+1:0], {`NORMSHIFTSZ-`DIVLEN-2-`NF{1'b0}}};
     // the quotent is in the range [.5,2)
     // if the quotent < 1 and not denormal then subtract 1 to account for the normalization shift
-    assign CorrDivExp = DivCalcExpM - {(`NE)'(0), ~Quot[`DIVLEN+2]};
+    assign CorrDivExp = (ResDenorm&~DenormShift[`NE+1]) ? (`NE+2)'(0) : DivCalcExpM - {(`NE+1)'(0), ~Quot[`DIVLEN+2]};
 
 endmodule
diff --git a/pipelined/src/fpu/postprocess.sv b/pipelined/src/fpu/postprocess.sv
index 9516e223f..b4c8496a3 100644
--- a/pipelined/src/fpu/postprocess.sv
+++ b/pipelined/src/fpu/postprocess.sv
@@ -88,6 +88,7 @@ module postprocess(
     logic [$clog2(`NORMSHIFTSZ)-1:0]  ShiftAmt;   // normalization shift count
     logic [$clog2(`NORMSHIFTSZ)-1:0]  DivShiftAmt;
     logic [`NORMSHIFTSZ-1:0]            ShiftIn;        // is the sum zero
+    logic [`NORMSHIFTSZ-1:0] DivShiftIn;
     logic [`NORMSHIFTSZ-1:0]    Shifted;    // the shifted result
     logic                   Plus1;      // add one to the final result?
     logic                   IntInvalid, Overflow, Underflow, Invalid; // flags
@@ -142,7 +143,7 @@ module postprocess(
                               .XZeroM, .IntToFp, .OutFmt, .CvtResUf, .CvtShiftIn);
     fmashiftcalc fmashiftcalc(.SumM, .ZExpM, .ProdExpM, .FmaNormCntM, .FmtM, .KillProdM, .ConvNormSumExp,
                           .ZDenormM, .SumZero, .PreResultDenorm, .FmaShiftAmt, .FmaShiftIn);
-    divshiftcalc divshiftcalc(.Quot, .DivCalcExpM, .CorrDivExp, .DivShiftAmt);
+    divshiftcalc divshiftcalc(.Quot, .DivCalcExpM, .CorrDivExp, .DivShiftAmt, .DivShiftIn);
 
     always_comb
         case(PostProcSelM)
@@ -156,7 +157,7 @@ module postprocess(
             end
             2'b01: begin //div ***prob can take out
                 ShiftAmt = DivShiftAmt;
-                ShiftIn =  {Quot[`DIVLEN+1:0], {`NORMSHIFTSZ-`DIVLEN-2{1'b0}}};
+                ShiftIn =  DivShiftIn;
             end
             default: begin 
                 ShiftAmt = {$clog2(`NORMSHIFTSZ){1'bx}}; 
diff --git a/pipelined/srt/srt-radix4.sv b/pipelined/srt/srt-radix4.sv
index eface008d..a49838ace 100644
--- a/pipelined/srt/srt-radix4.sv
+++ b/pipelined/srt/srt-radix4.sv
@@ -372,6 +372,6 @@ module expcalc(
 );
 
   // correct exponent for denormal shifts
-  assign DivCalcExp = (XExpE - XZeroCnt - YExpE + YZeroCnt + (`NE)'(`BIAS))&{`NE+1{~XZeroE}};
+  assign DivCalcExp = (XExpE - XZeroCnt - YExpE + YZeroCnt + (`NE)'(`BIAS))&{`NE+2{~XZeroE}};
 
 endmodule