Fix bug in f_enneper inbuilt isosurface function detected by static code analysis (CID 1372542-1372544).

Author: c-lipka

changes.txt

@@ -56,6 +56,8 @@ Changed Behaviour
     by directives (stuff that begins with `#`).
   - UV mapping of cylinder, cone and lemon primitives has been disabled again
     for now, due to their orientation being poorly defined.
+  - An age-old bug in the inbuilt `f_enneper` isosurface function has been
+    fixed; the function now results in the originally intended shape.
 
 New Features
 ------------
@@ -103,6 +105,7 @@ Reported by Coverity static code analysis:
 
   - CID 986462,986463 (Wrapper object use after free)
   - CID 967358-967362 (Uninitialized scalar variable)
+  - CID 1372542-1372544 (Result is not floating-point)
   - CID 1372618 (Uninitialized scalar variable)
   - CID 1372629 (Uninitialized pointer read)
   - CID 1372630-1372632 (Uninitialized scalar variable)

distribution/include/functions.inc

@@ -163,7 +163,12 @@
     // 2. y scale (inverse) 
     // 3. z scale (inverse)
 
-#declare f_enneper = function { internal(18) }
+#if (Functions_Inc_Temp < 3.8)
+    #declare deprecated once "f_enneper was broken prior to v3.8; results will most likely differ."
+             f_enneper = function { internal(18) }
+#else
+    #declare f_enneper = function { internal(18) }
+#end
 // Parameters: x, y, z
     // One extra parameter required: 
     // 1. Field strength

source/vm/fnintern.cpp

@@ -455,8 +455,8 @@ DBL f_enneper(FPUContext *ctx, DBL *ptr, unsigned int) // 18
     DBL r, r2,x2=PARAM_X*PARAM_X, y2=PARAM_Y*PARAM_Y, z2=PARAM_Z*PARAM_Z;
     if (fabs(PARAM_Z)<0.2)
         PARAM_Z=0.2;
-    r =((y2-x2)/(2*PARAM_Z)+2*z2/9+2/3);                  // TODO FIXME - was this supposed to be 2.0/3.0 ??
-    r2=((y2-x2)/(4*PARAM_Z)-(1/4)*(x2+y2+(8/9)*z2)+2/9);  // TODO FIXME - was this supposed to be 1.0/4.0, 8.0/9.0 and 2.0/9.0 respectively ??
+    r =((y2-x2)/(2*PARAM_Z)+2*z2/9+(2/3.));
+    r2=((y2-x2)/(4*PARAM_Z)-(1/4.)*(x2+y2+(8/9.)*z2)+(2/9.));
     r=-( r*r*r -6*r2*r2);
     return( min(10., max(PARAM(0)*r,-10.)) );
 }