From b0aa61088d6eec62fc5314844f4bd460ec451481 Mon Sep 17 00:00:00 2001
From: Aleksandar Andrejevic <aandrejevic@reactos.org>
Date: Wed, 20 May 2015 23:16:36 +0000
Subject: [PATCH] [FAST486] Fix a copy-paste bug. Adjust the number when
 subtracting in Fast486FpuAdd. Don't overflow the mantissa in
 Fast486FpuToSingle/Fast486FpuToDouble without correcting the exponent.

svn path=/trunk/; revision=67838
---
 reactos/lib/fast486/fpu.c | 79 +++++++++++++++++++++++++++------------
 1 file changed, 56 insertions(+), 23 deletions(-)

diff --git a/reactos/lib/fast486/fpu.c b/reactos/lib/fast486/fpu.c
index d64cee48ff1..ab778bd909b 100644
--- a/reactos/lib/fast486/fpu.c
+++ b/reactos/lib/fast486/fpu.c
@@ -430,14 +430,14 @@ Fast486FpuToSingleReal(PFAST486_STATE State,
     /* Calculate the remainder */
     Remainder = Value->Mantissa & ((1ULL << 40) - 1);
 
+    /* Store the biased exponent */
+    *Result |= (ULONG)(UnbiasedExp + FPU_REAL4_BIAS) << 23;
+
     /* Perform rounding */
     Result64 = (ULONGLONG)*Result;
     Fast486FpuRound(State, &Result64, Value->Sign, Remainder, 39);
     *Result = (ULONG)Result64;
 
-    /* Store the biased exponent */
-    *Result |= (ULONG)(UnbiasedExp + FPU_REAL4_BIAS) << 23;
-
 SetSign:
 
     if (Value->Sign) *Result |= 0x80000000;
@@ -529,12 +529,12 @@ Fast486FpuToDoubleReal(PFAST486_STATE State,
     /* Calculate the remainder */
     Remainder = Value->Mantissa & ((1 << 11) - 1);
 
-    /* Perform rounding */
-    Fast486FpuRound(State, Result, Value->Sign, Remainder, 10);
-
     /* Store the biased exponent */
     *Result |= (ULONGLONG)(UnbiasedExp + FPU_REAL8_BIAS) << 52;
 
+    /* Perform rounding */
+    Fast486FpuRound(State, Result, Value->Sign, Remainder, 10);
+
 SetSign:
 
     if (Value->Sign) *Result |= 1ULL << 63;
@@ -658,7 +658,7 @@ Fast486FpuAdd(PFAST486_STATE State,
     /* ... and the second one too */
     if (SecondAdjusted.Exponent < TempResult.Exponent)
     {
-        if ((TempResult.Exponent - FirstAdjusted.Exponent) < 64)
+        if ((TempResult.Exponent - SecondAdjusted.Exponent) < 64)
         {
             SecondAdjusted.Mantissa >>= (TempResult.Exponent - SecondAdjusted.Exponent);
             SecondAdjusted.Exponent = TempResult.Exponent;
@@ -693,31 +693,64 @@ Fast486FpuAdd(PFAST486_STATE State,
     }
 
     /* Did it overflow? */
-    if (FPU_IS_NORMALIZED(&FirstAdjusted) && FPU_IS_NORMALIZED(&SecondAdjusted))
+    if (FirstAdjusted.Sign == SecondAdjusted.Sign)
     {
-        if (TempResult.Exponent == FPU_MAX_EXPONENT)
+        if (TempResult.Mantissa < FirstAdjusted.Mantissa
+            || TempResult.Mantissa < SecondAdjusted.Mantissa)
         {
-            /* Raise the overflow exception */
-            State->FpuStatus.Oe = TRUE;
-
-            if (State->FpuControl.Om)
+            if (TempResult.Exponent == FPU_MAX_EXPONENT)
             {
-                /* Total overflow, return infinity */
-                TempResult.Mantissa = FPU_MANTISSA_HIGH_BIT;
-                TempResult.Exponent = FPU_MAX_EXPONENT + 1;
+                /* Raise the overflow exception */
+                State->FpuStatus.Oe = TRUE;
+
+                if (State->FpuControl.Om)
+                {
+                    /* Total overflow, return infinity */
+                    TempResult.Mantissa = FPU_MANTISSA_HIGH_BIT;
+                    TempResult.Exponent = FPU_MAX_EXPONENT + 1;
+                }
+                else
+                {
+                    Fast486FpuException(State);
+                    return FALSE;
+                }
             }
             else
             {
-                Fast486FpuException(State);
-                return FALSE;
+                /* Lose the LSB in favor of the carry */
+                TempResult.Mantissa >>= 1;
+                TempResult.Mantissa |= FPU_MANTISSA_HIGH_BIT;
+                TempResult.Exponent++;
             }
         }
-        else
+    }
+    else
+    {
+        if (TempResult.Mantissa >= FirstAdjusted.Mantissa
+            && TempResult.Mantissa >= SecondAdjusted.Mantissa)
         {
-            /* Lose the LSB in favor of the carry */
-            TempResult.Mantissa >>= 1;
-            TempResult.Mantissa |= FPU_MANTISSA_HIGH_BIT;
-            TempResult.Exponent++;
+            if (TempResult.Exponent == 0)
+            {
+                /* Raise the underflow exception */
+                State->FpuStatus.Ue = TRUE;
+
+                if (State->FpuControl.Um)
+                {
+                    /* Total overflow, return zero */
+                    TempResult.Mantissa = 0ULL;
+                }
+                else
+                {
+                    Fast486FpuException(State);
+                    return FALSE;
+                }
+            }
+            else
+            {
+                /* Lose the MSB */
+                TempResult.Mantissa <<= 1;
+                TempResult.Exponent--;
+            }
         }
     }