[aandrejevic] 60969: [FAST486] Fix several bugs in Fast486RotateOperation.

Author: aandrejevic
Date: Wed Nov 13 02:38:36 2013
New Revision: 60969

URL: http://svn.reactos.org/svn/reactos?rev=60969&view=rev
Log:
[FAST486]
Fix several bugs in Fast486RotateOperation.

Modified:
    branches/ntvdm/lib/fast486/opgroups.c

Modified: branches/ntvdm/lib/fast486/opgroups.c
URL: http://svn.reactos.org/svn/reactos/branches/ntvdm/lib/fast486/opgroups.c?rev...
==============================================================================
--- branches/ntvdm/lib/fast486/opgroups.c	[iso-8859-1] (original)
+++ branches/ntvdm/lib/fast486/opgroups.c	[iso-8859-1] Wed Nov 13 02:38:36 2013
@@ -161,17 +161,17 @@
                        UCHAR Count)
 {
     ULONG HighestBit = 1 << (Bits - 1);
+    ULONG MaxValue = HighestBit | (HighestBit - 1);
     ULONG Result;

/* Normalize the count */
     Count &= 0x1F;

+    if (Operation <= 1) Count %= Bits;
+    else if (Operation <= 3) Count %= Bits + 1;
+
     /* If the count is zero, do nothing */
-    if (Count == 0)
-    {
-        Result = Value;
-        goto SetFlags;
-    }
+    if (Count == 0) return Value;

/* Check which operation is this */
     switch (Operation)
@@ -205,9 +205,40 @@
         /* RCL */
         case 2:
         {
-            Result = (Value << Count)
-                     | (State->Flags.Cf << (Count - 1))
-                     | (Value >> (Bits - Count + 1));
+            Result = (Value << Count) | (State->Flags.Cf << (Count - 1));
+            
+            /* Complete the calculation, but make sure we don't shift by too much */
+            if ((Bits - Count) < 31) Result |= Value >> (Bits - Count + 1);
+
+            /* Update CF and OF */
+            State->Flags.Cf = ((Value & (1 << (Bits - Count))) != 0);
+            if (Count == 1) State->Flags.Of = State->Flags.Cf ^ ((Result & HighestBit) != 0);
+
+            break;
+        }
+
+        /* RCR */
+        case 3:
+        {
+            /* Update OF */
+            if (Count == 1) State->Flags.Of = State->Flags.Cf ^ ((Value & HighestBit) != 0);
+
+            Result = (Value >> Count) | (State->Flags.Cf << (Bits - Count));
+
+            /* Complete the calculation, but make sure we don't shift by too much */
+            if ((Bits - Count) < 31) Result |= Value << (Bits - Count + 1);
+
+            /* Update CF */
+            State->Flags.Cf = ((Value & (1 << (Count - 1))) != 0);
+
+            break;
+        }
+
+        /* SHL/SAL */
+        case 4:
+        case 6:
+        {
+            Result = Value << Count;

/* Update CF and OF */
             State->Flags.Cf = ((Value & (1 << (Bits - Count))) != 0);
@@ -217,35 +248,6 @@
             break;
         }

-        /* RCR */
-        case 3:
-        {
-            Result = (Value >> Count)
-                     | (State->Flags.Cf << (Bits - Count))
-                     | (Value << (Bits - Count + 1));
-
-            /* Update CF and OF */
-            State->Flags.Cf = ((Value & (1 << (Bits - Count))) != 0);
-            if (Count == 1) State->Flags.Of = State->Flags.Cf
-                                              ^ ((Result & (HighestBit >> 1)) != 0);
-
-            break;
-        }
-
-        /* SHL/SAL */
-        case 4:
-        case 6:
-        {
-            Result = Value << Count;
-
-            /* Update CF and OF */
-            State->Flags.Cf = ((Value & (1 << (Bits - Count))) != 0);
-            if (Count == 1) State->Flags.Of = State->Flags.Cf
-                                              ^ ((Result & HighestBit) != 0);
-
-            break;
-        }
-
         /* SHR */
         case 5:
         {
@@ -274,11 +276,10 @@
         }
     }

-SetFlags:
     if (Operation >= 4)
     {
         /* Update ZF, SF and PF */
-        State->Flags.Zf = (Result == 0);
+        State->Flags.Zf = ((Result & MaxValue) == 0);
         State->Flags.Sf = ((Result & HighestBit) != 0);
         State->Flags.Pf = Fast486CalculateParity(Result);
     }