From 7ffa7667b6f31d27cda7c2c15a7e330055eb0385 Mon Sep 17 00:00:00 2001
From: Eyck-Alexander Jentzsch <alex@minres.com>
Date: Mon, 29 Jul 2024 21:07:54 +0200
Subject: [PATCH] fixes concerning FMADD_S, FMSUB_S, FNMADD_S, and FNSUB_S
 mostly about ensuring correct sign

---
 softfloat/source/s_mulAddF32.c | 8 ++++++--
 src/vm/fp_functions.cpp        | 8 +++++++-
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/softfloat/source/s_mulAddF32.c b/softfloat/source/s_mulAddF32.c
index 805517c..94c21eb 100644
--- a/softfloat/source/s_mulAddF32.c
+++ b/softfloat/source/s_mulAddF32.c
@@ -92,11 +92,14 @@ float32_t
         goto infProdArg;
     }
     if ( expC == 0xFF ) {
+        // expC indicates special value
         if ( sigC ) {
+            //uiC is quiet NaN
             uiZ = 0;
             goto propagateNaN_ZC;
         }
-        uiZ = uiC;
+        //uiC is +- infinity
+        uiZ =  (uiC & ~(1UL << 31)) | ((unsigned long)signC << 31); //set sign bit
         goto uiZ;
     }
     /*------------------------------------------------------------------------
@@ -209,12 +212,13 @@ float32_t
     /*------------------------------------------------------------------------
     *------------------------------------------------------------------------*/
  zeroProd:
-    uiZ = uiC;
+    uiZ = (uiC & ~(1UL << 31)) | ((unsigned long)signC << 31); //set sign bit
     if ( ! (expC | sigC) && (signProd != signC) ) {
  completeCancellation:
         uiZ =
             packToF32UI(
                 (softfloat_roundingMode == softfloat_round_min), 0, 0 );
+    uiZ = (uiZ & ~(1UL << 31)) | ((unsigned long)(signC|signProd) << 31); //set sign bit            
     }
  uiZ:
     uZ.ui = uiZ;
diff --git a/src/vm/fp_functions.cpp b/src/vm/fp_functions.cpp
index cad3b06..ad340b5 100644
--- a/src/vm/fp_functions.cpp
+++ b/src/vm/fp_functions.cpp
@@ -149,11 +149,17 @@ uint32_t fcvt_s(uint32_t v1, uint32_t op, uint8_t mode) {
 }
 
 uint32_t fmadd_s(uint32_t v1, uint32_t v2, uint32_t v3, uint32_t op, uint8_t mode) {
+    // Used values for op are:
+    // FMADD_S:  0b00
+    // FMSUB_S:  0b01
+    // FNMADD_S: 0b10
+    // FNMSUB_S: 0b11
     // op should be {softfloat_mulAdd_subProd(2), softfloat_mulAdd_subC(1)}
     softfloat_roundingMode = rmm_map[mode & 0x7];
     softfloat_exceptionFlags = 0;
     float32_t res = softfloat_mulAddF32(v1, v2, v3, op & 0x1);
-    if(op > 1)
+    // Do not invert quiet NaN
+    if((op & 0b10) && (res.v != quiet_nan32))
         res.v ^= 1ULL << 31;
     return res.v;
 }