Re-implement SlopeDiv with approximate division

Author: jserv

src/doomtype.h

@@ -56,8 +56,10 @@ typedef unsigned char byte;
 
 #if defined(__GNUC__) || defined(__clang__)
 #define CONSTFUNC __attribute__((const))
+#define PUREFUNC __attribute__((pure))
 #else
 #define CONSTFUNC
+#define PUREFUNC
 #endif
 
 #endif

src/m_fixed.h

@@ -63,7 +63,7 @@ inline static int CONSTFUNC D_abs(fixed_t x)
  * Fixed Point Multiplication
  */
 
-inline fixed_t CONSTFUNC FixedMul(fixed_t a, fixed_t b)
+inline static fixed_t CONSTFUNC FixedMul(fixed_t a, fixed_t b)
 {
     return (fixed_t)((int64_t) a * b >> FRACBITS);
 }

src/r_main.c

@@ -150,11 +150,11 @@ R_AddPointToBox
 //  check point against partition plane.
 // Returns side 0 (front) or 1 (back).
 //
-int
+PUREFUNC int
 R_PointOnSide
 ( fixed_t       x,
   fixed_t       y,
-  node_t*       node )
+  const node_t*       node )
 {
     fixed_t     dx;
     fixed_t     dy;
@@ -265,6 +265,17 @@ R_PointOnSegSide
     return 1;
 }
 
+static CONSTFUNC int SlopeDiv(unsigned num, unsigned den)
+{
+    den = den >> 8;
+
+    if (den == 0)
+        return SLOPERANGE;
+
+    const unsigned int ans = FixedApproxDiv(num << 3, den) >> FRACBITS;
+
+    return (ans <= SLOPERANGE) ? ans : SLOPERANGE;
+}
 
 //
 // R_PointToAngle
@@ -275,11 +286,6 @@ R_PointOnSegSide
 //  tangent (slope) value which is looked up in the
 //  tantoangle[] table.
 
-//
-
-
-
-
 angle_t
 R_PointToAngle
 ( fixed_t       x,

src/r_main.h

@@ -98,11 +98,11 @@ extern void             (*colfunc) (void);
 
 //
 // Utility functions.
-int
+PUREFUNC int
 R_PointOnSide
 ( fixed_t       x,
   fixed_t       y,
-  node_t*       node );
+  const node_t*       node );
 
 int
 R_PointOnSegSide

src/tables.c

@@ -43,26 +43,6 @@ rcsid[] = "$Id: tables.c,v 1.4 1997/02/03 16:47:57 b1 Exp $";
 #include "tables.h"
 
 
-
-
-int
-SlopeDiv
-( unsigned      num,
-  unsigned      den)
-{
-    unsigned    ans;
-
-    if (den < 512)
-        return SLOPERANGE;
-
-    ans = (num<<3)/(den>>8);
-
-    return ans <= SLOPERANGE ? ans : SLOPERANGE;
-}
-
-
-
-
 int finetangent[4096] =
 {
     -170910304,-56965752,-34178904,-24413316,-18988036,-15535599,-13145455,-11392683,

src/tables.h

@@ -76,15 +76,6 @@ typedef unsigned angle_t;
 //  without additional checking.
 extern angle_t          tantoangle[SLOPERANGE+1];
 
-
-// Utility function,
-//  called by R_PointToAngle.
-int
-SlopeDiv
-( unsigned      num,
-  unsigned      den);
-
-
 #endif
 //-----------------------------------------------------------------------------
 //