[aandrejevic] 67932: [FAST486] Implement FPTAN by calculating the sine and then dividing it by the approximated cosine: sqrt(1 - sin(x) ^ 2). This method turned out to be faster and more precise th...

Author: aandrejevic
Date: Tue May 26 19:11:33 2015
New Revision: 67932

URL: http://svn.reactos.org/svn/reactos?rev=67932&view=rev
Log:
[FAST486]
Implement FPTAN by calculating the sine and then dividing it by
the approximated cosine: sqrt(1 - sin(x) ^ 2).
This method turned out to be faster and more precise than the
Maclaurin series for tan(x), which converges very slowly.


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=6793…
==============================================================================
--- trunk/reactos/lib/fast486/fpu.c	[iso-8859-1] (original)
+++ trunk/reactos/lib/fast486/fpu.c	[iso-8859-1] Tue May 26 19:11:33 2015
@@ -1173,7 +1173,7 @@
  */
 static inline VOID FASTCALL
 Fast486FpuCalculateTwoPowerMinusOne(PFAST486_STATE State,
-                                    PFAST486_FPU_DATA_REG Operand,
+                                    PCFAST486_FPU_DATA_REG Operand,
                                     PFAST486_FPU_DATA_REG Result)
 {
     INT i;
@@ -1221,7 +1221,7 @@
 
 static inline BOOLEAN FASTCALL
 Fast486FpuCalculateLogBase2(PFAST486_STATE State,
-                            PFAST486_FPU_DATA_REG Operand,
+                            PCFAST486_FPU_DATA_REG Operand,
                             PFAST486_FPU_DATA_REG Result)
 {
     INT i;
@@ -1345,7 +1345,7 @@
  */
 static inline BOOLEAN FASTCALL
 Fast486FpuCalculateSine(PFAST486_STATE State,
-                        PFAST486_FPU_DATA_REG Operand,
+                        PCFAST486_FPU_DATA_REG Operand,
                         PFAST486_FPU_DATA_REG Result)
 {
     INT i;
@@ -1425,7 +1425,7 @@
  */
 static inline BOOLEAN FASTCALL
 Fast486FpuCalculateCosine(PFAST486_STATE State,
-                          PFAST486_FPU_DATA_REG Operand,
+                          PCFAST486_FPU_DATA_REG Operand,
                           PFAST486_FPU_DATA_REG Result)
 {
     FAST486_FPU_DATA_REG Value = *Operand;
@@ -2136,9 +2136,23 @@
             /* FPTAN */
             case 0x32:
             {
-                // TODO: NOT IMPLEMENTED
-                UNIMPLEMENTED;
-
+                FAST486_FPU_DATA_REG Sine;
+                FAST486_FPU_DATA_REG Cosine;
+
+                /* Compute the sine */
+                if (!Fast486FpuCalculateSine(State, &FPU_ST(0), &Sine)) break;
+
+                /* Find the cosine by calculating sqrt(1 - sin(x) ^ 2) */
+                if (!Fast486FpuMultiply(State, &Sine, &Sine, &Cosine))
break;
+                if (!Fast486FpuSubtract(State, &FpuOne, &Cosine, &Cosine))
break;
+                if (!Fast486FpuCalculateSquareRoot(State, &Cosine, &Cosine))
break;
+
+                /* Divide the sine by the cosine to get the tangent */
+                if (!Fast486FpuDivide(State, &Sine, &Cosine, &FPU_ST(0)))
break;
+                FPU_UPDATE_TAG(0);
+
+                /* Push 1.00 */
+                Fast486FpuPush(State, &FpuOne);
                 break;
             }