[aandrejevic] 67820: [FAST486] Fix several division related problems: - In UnsignedDivMod128, fix the leading zero calculation for 128-bit numbers. - In Fast486FpuDivide, there's no need to increas...

Author: aandrejevic
Date: Mon May 18 12:17:40 2015
New Revision: 67820

URL: http://svn.reactos.org/svn/reactos?rev=67820&view=rev
Log:
[FAST486]
Fix several division related problems:
- In UnsignedDivMod128, fix the leading zero calculation for 128-bit numbers.
- In Fast486FpuDivide, there's no need to increase the exponent by 64 (adding zeros
at the end of a number after the decimal point changes nothing).
- FDIV/FDIVR were reversed

Modified:
    trunk/reactos/lib/fast486/fpu.c

Modified: trunk/reactos/lib/fast486/fpu.c
URL: http://svn.reactos.org/svn/reactos/trunk/reactos/lib/fast486/fpu.c?rev=67820...
==============================================================================
--- trunk/reactos/lib/fast486/fpu.c	[iso-8859-1] (original)
+++ trunk/reactos/lib/fast486/fpu.c	[iso-8859-1] Mon May 18 12:17:40 2015
@@ -203,9 +203,9 @@
      * Calculate the number of significant bits the current
      * divisor has more than the original divisor
      */
-    Bits = CountLeadingZeros64(Divisor) + 64;
-    Bits -= (CurrentHigh > 0ULL) ? CountLeadingZeros64(CurrentHigh) : 64;
-    Bits -= (CurrentLow > 0ULL) ? CountLeadingZeros64(CurrentLow) : 64;
+    Bits = CountLeadingZeros64(Divisor);
+    if (CurrentHigh > 0ULL) Bits -= CountLeadingZeros64(CurrentHigh);
+    else Bits -= CountLeadingZeros64(CurrentLow);

if (Bits)
     {
@@ -923,11 +923,10 @@
     }

/* Calculate the exponent of the result */
-    Exponent = (LONG)FirstOperand->Exponent - (LONG)SecondOperand->Exponent - 64;
+    Exponent = (LONG)FirstOperand->Exponent - (LONG)SecondOperand->Exponent - 1;

/* Divide the two mantissas */
     Remainder = UnsignedDivMod128(0ULL,
-                                  /* Notice the 64 above - this is the high part */
                                   FirstOperand->Mantissa,
                                   SecondOperand->Mantissa,
                                   &QuotientLow,
@@ -1169,14 +1168,14 @@
         /* FDIV */
         case 6:
         {
-            Fast486FpuDivide(State, DestOperand, SourceOperand, DestOperand);
+            Fast486FpuDivide(State, SourceOperand, DestOperand, DestOperand);
             break;
         }

/* FDIVR */
         case 7:
         {
-            Fast486FpuDivide(State, SourceOperand, DestOperand, DestOperand);
+            Fast486FpuDivide(State, DestOperand, SourceOperand, DestOperand);
             break;
         }
     }