From d5ba8fc5e6f4b54a98dc7629e651ed8f6742b7b8 Mon Sep 17 00:00:00 2001
From: David Harris <David_Harris@hmc.edu>
Date: Fri, 10 Nov 2023 18:33:08 -0800
Subject: [PATCH] fdivsqrt parameter cleanup

---
 config/shared/config-shared.vh  | 10 ++++++++--
 config/shared/parameter-defs.vh |  1 -
 src/cvw.sv                      |  1 -
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/config/shared/config-shared.vh b/config/shared/config-shared.vh
index 10b56f24e..12967764f 100644
--- a/config/shared/config-shared.vh
+++ b/config/shared/config-shared.vh
@@ -93,11 +93,17 @@ localparam NF2   = ((F_SUPPORTED & (LEN1 != S_LEN)) ? S_NF   : H_NF);
 localparam FMT2  = ((F_SUPPORTED & (LEN1 != S_LEN)) ? 2'd0    : 2'd2);
 localparam BIAS2 = ((F_SUPPORTED & (LEN1 != S_LEN)) ? S_BIAS : H_BIAS);
 
+// intermediate division parameters not directly used in Divider
+localparam FPDIVN      = NF+3; // length of floating-point inputs: Ns + 2 = Nf + 3 for 1 integer bit, Nf fracitonal bits, 2 extra bits to shift sqrt into [1/4, 1)]
+localparam DIVN        = ((FPDIVN<XLEN) & IDIV_ON_FPU) ? XLEN : FPDIVN+3; // standard length of input: max(XLEN, NF+2) ***
+
 // division constants
-localparam DIVN        = ((NF+2<XLEN) & IDIV_ON_FPU) ? XLEN : NF+2; // standard length of input: max(XLEN, NF+2)
+
+// *** define NF+2, justify, use in DIVN
 localparam LOGR        = $clog2(RADIX);                             // r = log(R)
 localparam RK          = LOGR*DIVCOPIES;                            // r*k bits per cycle generated
-localparam FPDUR       = (DIVN+1)/RK + 1 + (RADIX/4);               // *** relate to algorithm for rest of these
+//localparam FPDUR       = (DIVN+1)/RK + 1 + (RADIX/4);               // *** relate to algorithm for rest of these
+localparam FPDUR       = (DIVN+LOGR-1)/RK + 1 ;               // ceiling((DIVN+LOGR)/RK)
 localparam DURLEN      = $clog2(FPDUR+1);
 localparam DIVb        = FPDUR*RK - 1; // canonical fdiv size (b)
 localparam DIVBLEN     = $clog2(DIVb+2)-1;                          // *** where is 2 coming from?
diff --git a/config/shared/parameter-defs.vh b/config/shared/parameter-defs.vh
index 85c9d1c19..57d61fc00 100644
--- a/config/shared/parameter-defs.vh
+++ b/config/shared/parameter-defs.vh
@@ -177,7 +177,6 @@ localparam cvw_t P = '{
   NORMSHIFTSZ : NORMSHIFTSZ,
   LOGNORMSHIFTSZ : LOGNORMSHIFTSZ,
   CORRSHIFTSZ : CORRSHIFTSZ,
-  DIVN        : DIVN,
   LOGR        : LOGR,
   RK          : RK,
   FPDUR       : FPDUR,
diff --git a/src/cvw.sv b/src/cvw.sv
index 3c32982bd..cc968b803 100644
--- a/src/cvw.sv
+++ b/src/cvw.sv
@@ -269,7 +269,6 @@ typedef struct packed {
   int CORRSHIFTSZ;
 
 // division constants
-  int DIVN       ;
   int LOGR       ;
   int RK         ;
   int FPDUR      ;