From 632d8780deab9576847a51228129b782f8e8c18b Mon Sep 17 00:00:00 2001
From: Stanislav Shwartsman <sshwarts@users.sourceforge.net>
Date: Sun, 28 Apr 2024 06:41:29 +0300
Subject: [PATCH] rewrite code for biasing unmasked underflow for floatx80 in
 softfloat3e (from hack to clean code)

---
 bochs/cpu/softfloat3e/s_roundPackToExtF80.c | 104 ++++++++++----------
 1 file changed, 53 insertions(+), 51 deletions(-)

diff --git a/bochs/cpu/softfloat3e/s_roundPackToExtF80.c b/bochs/cpu/softfloat3e/s_roundPackToExtF80.c
index b0d4039ba..fea854024 100644
--- a/bochs/cpu/softfloat3e/s_roundPackToExtF80.c
+++ b/bochs/cpu/softfloat3e/s_roundPackToExtF80.c
@@ -76,25 +76,29 @@ extFloat80_t
             /*----------------------------------------------------------------
             *----------------------------------------------------------------*/
             isTiny = (exp < 0) || (sig <= (uint64_t) (sig + roundIncrement));
-            sig = softfloat_shiftRightJam64(sig, 1 - exp);
-            sigExact = sig;
-            roundBits = sig & roundMask;
-            sig += roundIncrement;
-            exp = ((sig & UINT64_C(0x8000000000000000)) != 0);
-            roundIncrement = roundMask + 1;
-            if (roundNearEven && (roundBits<<1 == roundIncrement)) {
-                roundMask |= roundIncrement;
+            if (isTiny && sig && ! softfloat_isMaskedException(status, softfloat_flag_underflow)) {
+                softfloat_raiseFlags(status, softfloat_flag_underflow);
+                exp += 0x6000;
             }
-            sig &= ~roundMask;
-            if (isTiny) {
-                if (roundBits || (sig && ! softfloat_isMaskedException(status, softfloat_flag_underflow)))
-                    softfloat_raiseFlags(status, softfloat_flag_underflow);
+            else {
+                sig = softfloat_shiftRightJam64(sig, 1 - exp);
+                roundBits = sig & roundMask;
+                sigExact = sig;
+                sig += roundIncrement;
+                exp = ((sig & UINT64_C(0x8000000000000000)) != 0);
+                roundIncrement = roundMask + 1;
+                if (roundNearEven && (roundBits<<1 == roundIncrement)) {
+                    roundMask |= roundIncrement;
+                }
+                sig &= ~roundMask;
+                if (roundBits) {
+                    softfloat_raiseFlags(status, softfloat_flag_inexact);
+                    if (sig > sigExact) softfloat_setRoundingUp(status);
+                    if (isTiny)
+                        softfloat_raiseFlags(status, softfloat_flag_underflow);
+                }
+                return packToExtF80(sign, exp, sig);
             }
-            if (roundBits) {
-                softfloat_raiseFlags(status, softfloat_flag_inexact);
-                if (sig > sigExact) softfloat_setRoundingUp(status);
-            }
-            return packToExtF80(sign, exp, sig);
         }
         if ((0x7FFE < exp) || ((exp == 0x7FFE) && ((uint64_t) (sig + roundIncrement) < sig))) {
             goto overflow;
@@ -102,9 +106,6 @@ extFloat80_t
     }
     /*------------------------------------------------------------------------
     *------------------------------------------------------------------------*/
-    if (roundBits) {
-        softfloat_raiseFlags(status, softfloat_flag_inexact);
-    }
     sigExact = sig;
     sig = (uint64_t) (sig + roundIncrement);
     if (sig < roundIncrement) {
@@ -117,7 +118,10 @@ extFloat80_t
         roundMask |= roundIncrement;
     }
     sig &= ~roundMask;
-    if (sig > sigExact) softfloat_setRoundingUp(status);
+    if (roundBits) {
+        softfloat_raiseFlags(status, softfloat_flag_inexact);
+        if (sig > sigExact) softfloat_setRoundingUp(status);
+    }
     return packToExtF80(sign, exp, sig);
     /*------------------------------------------------------------------------
     *------------------------------------------------------------------------*/
@@ -134,30 +138,35 @@ extFloat80_t
             /*----------------------------------------------------------------
             *----------------------------------------------------------------*/
             isTiny = (exp < 0) || ! doIncrement || (sig < UINT64_C(0xFFFFFFFFFFFFFFFF));
-            sig64Extra = softfloat_shiftRightJam64Extra(sig, sigExtra, 1 - exp);
-            exp = 0;
-            sig = sig64Extra.v;
-            sigExtra = sig64Extra.extra;
-            if (isTiny) {
-                if (sigExtra || (sig && ! softfloat_isMaskedException(status, softfloat_flag_underflow)))
-                    softfloat_raiseFlags(status, softfloat_flag_underflow);
+            if (isTiny && sig && ! softfloat_isMaskedException(status, softfloat_flag_underflow)) {
+                softfloat_raiseFlags(status, softfloat_flag_underflow);
+                exp += 0x6000;
             }
-            if (sigExtra)
-                softfloat_raiseFlags(status, softfloat_flag_inexact);
-            doIncrement = (UINT64_C(0x8000000000000000) <= sigExtra);
-            if (! roundNearEven && (roundingMode != softfloat_round_near_maxMag)) {
-                doIncrement =
-                    (roundingMode == (sign ? softfloat_round_min : softfloat_round_max)) && sigExtra;
+            else {
+                sig64Extra = softfloat_shiftRightJam64Extra(sig, sigExtra, 1 - exp);
+                exp = 0;
+                sig = sig64Extra.v;
+                sigExtra = sig64Extra.extra;
+                if (sigExtra) {
+                    softfloat_raiseFlags(status, softfloat_flag_inexact);
+                    if (isTiny)
+                        softfloat_raiseFlags(status, softfloat_flag_underflow);
+                }
+                doIncrement = (UINT64_C(0x8000000000000000) <= sigExtra);
+                if (! roundNearEven && (roundingMode != softfloat_round_near_maxMag)) {
+                    doIncrement =
+                        (roundingMode == (sign ? softfloat_round_min : softfloat_round_max)) && sigExtra;
+                }
+                if (doIncrement) {
+                    sigExact = sig;
+                    ++sig;
+                    sig &= ~(uint64_t) (! (sigExtra & UINT64_C(0x7FFFFFFFFFFFFFFF)) & roundNearEven);
+                    exp = ((sig & UINT64_C(0x8000000000000000)) != 0);
+                    if (sig > sigExact)
+                        softfloat_setRoundingUp(status);
+                }
+                return packToExtF80(sign, exp, sig);
             }
-            if (doIncrement) {
-                sigExact = sig;
-                ++sig;
-                sig &= ~(uint64_t) (! (sigExtra & UINT64_C(0x7FFFFFFFFFFFFFFF)) & roundNearEven);
-                exp = ((sig & UINT64_C(0x8000000000000000)) != 0);
-                if (sig > sigExact)
-                    softfloat_setRoundingUp(status);
-            }
-            return packToExtF80(sign, exp, sig);
         }
         if ((0x7FFE < exp) || ((exp == 0x7FFE) && (sig == UINT64_C(0xFFFFFFFFFFFFFFFF)) && doIncrement)) {
             /*----------------------------------------------------------------
@@ -206,18 +215,11 @@ extFloat80_t
 extFloat80_t
  softfloat_roundPackToExtF80(bool sign, int32_t exp, uint64_t sig, uint64_t sigExtra, uint8_t roundingPrecision, struct softfloat_status_t *status)
 {
-    softfloat_status_t round_status = *status;
     extFloat80_t result = SoftFloat_roundPackToExtF80(sign, exp, sig, sigExtra, roundingPrecision, status);
 
-    // bias unmasked underflow
-    if (status->softfloat_exceptionFlags & ~status->softfloat_exceptionMasks & softfloat_flag_underflow) {
-        softfloat_raiseFlags(&round_status, softfloat_flag_underflow);
-        result = SoftFloat_roundPackToExtF80(sign, exp + 0x6000, sig, sigExtra, roundingPrecision, &round_status);
-        *status = round_status;
-    }
-
     // bias unmasked overflow
     if (status->softfloat_exceptionFlags & ~status->softfloat_exceptionMasks & softfloat_flag_overflow) {
+        softfloat_status_t round_status = *status;
         softfloat_raiseFlags(&round_status, softfloat_flag_overflow);
         result = SoftFloat_roundPackToExtF80(sign, exp - 0x6000, sig, sigExtra, roundingPrecision, &round_status);
         *status = round_status;