From 7629173b152f6ab6d12c7a6070c5db09bbb61d3d Mon Sep 17 00:00:00 2001
From: cturek <cturek@hmc.edu>
Date: Wed, 13 Jul 2022 22:42:39 +0000
Subject: [PATCH] DIVLEN and counter updated for sqrt computation and rounding

---
 pipelined/config/shared/wally-shared.vh |  2 +-
 pipelined/srt/srt-waves.do              |  2 +-
 pipelined/srt/srt.sv                    | 35 +++++++++----------------
 3 files changed, 14 insertions(+), 25 deletions(-)

diff --git a/pipelined/config/shared/wally-shared.vh b/pipelined/config/shared/wally-shared.vh
index ad52be2e..73810c68 100644
--- a/pipelined/config/shared/wally-shared.vh
+++ b/pipelined/config/shared/wally-shared.vh
@@ -103,7 +103,7 @@
 // division constants
 `define RADIX 32'h4
 `define DIVCOPIES 32'h4
-`define DIVLEN ((`NF < `XLEN) ? (`XLEN) : (`NF + 1))
+`define DIVLEN ((`NF < `XLEN) ? (`XLEN + 2) : (`NF + 2))
 `define DIVRESLEN ((`NF>`XLEN) ? `DIVLEN+2 : `DIVLEN)
 `define LOGR ((`RADIX==2) ? 32'h1 : 32'h2)
 // FPDUR = ceil(DIVRESLEN/(LOGR*DIVCOPIES))
diff --git a/pipelined/srt/srt-waves.do b/pipelined/srt/srt-waves.do
index 340c5b1f..1e0c3f28 100644
--- a/pipelined/srt/srt-waves.do
+++ b/pipelined/srt/srt-waves.do
@@ -1,5 +1,5 @@
 add wave -noupdate /testbench/*
 add wave -noupdate /testbench/srt/*
-add wave -noupdate /testbench/srt/otfc2/*
+add wave -noupdate /testbench/srt/sotfc2/*
 add wave -noupdate /testbench/srt/preproc/*
 add wave -noupdate /testbench/srt/divcounter/*
diff --git a/pipelined/srt/srt.sv b/pipelined/srt/srt.sv
index 4cd23488..74ce48cd 100644
--- a/pipelined/srt/srt.sv
+++ b/pipelined/srt/srt.sv
@@ -29,8 +29,8 @@
 ////////////////////////////////////////////////////////////////////////////////////////////////
 
 `include "wally-config.vh"
-`define EXTRAFRACBITS ((`NF<(`XLEN)) ? (`XLEN - `NF) : 0)
-`define EXTRAINTBITS ((`NF<(`XLEN)) ? 0 : (`NF - `XLEN + 1))
+`define EXTRAFRACBITS ((`NF<(`XLEN)) ? (`XLEN - `NF + 2) : 2)
+`define EXTRAINTBITS ((`NF<(`XLEN)) ? 2 : (`NF - `XLEN + 2))
 
 module srt (
   input  logic clk,
@@ -49,7 +49,7 @@ module srt (
   input  logic       Int, // Choose integer inputs
   input  logic       Sqrt, // perform square root, not divide
   output logic       rsign, done,
-  output logic [`DIVLEN-1:0] Rem, Quot, // *** later handle integers
+  output logic [`DIVLEN-3:0] Rem, Quot, // *** later handle integers
   output logic [`NE-1:0] rExp,
   output logic [3:0] Flags
 );
@@ -164,7 +164,7 @@ module srtpreproc (
   assign intSign = Signed & (SrcA[`XLEN - 1] ^ SrcB[`XLEN - 1]);
 
   // Number of cycles of divider
-  assign dur = Int ? (intExp & {7{~intExp[6]}}) : (7)'(`DIVLEN + 2);
+  assign dur = Int ? (intExp & {7{~intExp[6]}}) : (7)'(`DIVLEN);
 endmodule
 
 /////////////////////////////////
@@ -226,26 +226,16 @@ endmodule
 ///////////////////////////////////
 // On-The-Fly Converter, Radix 2 //
 ///////////////////////////////////
-module otfc2 #(parameter N=64) (
+module otfc2 #(parameter N=66) (
   input  logic         clk,
   input  logic         Start,
   input  logic         qp, qz, qn,
-  output logic [N-1:0] r
+  output logic [N-3:0] r
 );
-
   //  The on-the-fly converter transfers the quotient 
-  //  bits to the quotient as they come. 
-  //
-  //  This code follows the psuedocode presented in the 
-  //  floating point chapter of the book. Right now, 
-  //  it is written for Radix-2 division.
-  //
-  //  QM is Q-1. It allows us to write negative bits 
-  //  without using a costly CPA. 
+  //  bits to the quotient as they come.
+  //  Use this otfc for division only.
   logic [N+2:0] Q, QM, QNext, QMNext, QMMux;
-  //  QR and QMR are the shifted versions of Q and QM.
-  //  They are treated as [N-1:r] size signals, and 
-  //  discard the r most significant bits of Q and QM. 
   logic [N+1:0] QR, QMR;
 
   flopr #(N+3) Qreg(clk, Start, QNext, Q);
@@ -266,7 +256,7 @@ module otfc2 #(parameter N=64) (
       QMNext = {QMR, 1'b0};
     end 
   end
-  assign r = Q[N+2] ? Q[N+1:2] : Q[N:1];
+  assign r = Q[N] ? Q[N-1:2] : Q[N-2:1];
 
 endmodule
 
@@ -278,13 +268,12 @@ module sotfc2(
   input  logic         Start,
   input  logic         sp, sn,
   input  logic [`DIVLEN+3:0] C,
-  output logic [`DIVLEN-1:0] Sq,
+  output logic [`DIVLEN-3:0] Sq,
   output logic [`DIVLEN+3:0] F
 );
-
-
   //  The on-the-fly converter transfers the square root 
   //  bits to the quotient as they come.
+  //  Use this otfc for division and square root.
   logic [`DIVLEN+3:0] S, SM, SNext, SMNext, SMux;
 
   flopr #(`DIVLEN+4) Sreg(clk, Start, SMNext, SM);
@@ -303,7 +292,7 @@ module sotfc2(
       SMNext = SM | ((C << 2) & ~(C << 1));
     end 
   end
-  assign Sq = S[`DIVLEN-1:0];
+  assign Sq = S[`DIVLEN] ? S[`DIVLEN-1:2] : S[`DIVLEN-2:1];
 
   fsel2 fsel(sp, sn, C, S, SM, F);