runner% cat prepro.c
#define MIN(x, y) (((x) < (y)) ? (x) : (y))
#define MIN4(a, b, c, d) MIN(MIN(a, b), MIN(c, d))
#define  BETA  0.292893218813452476
#define f(x)  ((x) < -BETA) ? (-2.0*((x)+1.0)*((x)+1.0))  \
             : (((x) <= 0) ? (-2.0*(x)*((x)+2.0))  \
             : (((x) < BETA) ? (2.0*(x)*(2.0-(x)))  \
             : (-2.0*(1.0-(x))*(1.0-(x)))))
/*#define DEBUG */

void main()
{
        int u = 1, v = 2, r = 3, s = 4, t = 5;
        double y = 1.0, z;
        u = MIN(u, v);
        v = MIN4(r, s, t, u);
        z = f(y);
#ifdef DEBUG
        printf("%f\n", z);
        printf("%i, %i\n", u, v);
#else
        printf("No debuggin\n");
#endif
}
runner% cc -E prepro.c > prepro.out
runner% cat prepro.out
# 8 "prepro.c"
 
void main()
{
        int u = 1, v = 2, r = 3, s = 4, t = 5;
        double y = 1.0, z;
        u =  ( ( ( u ) < ( v ) ) ? ( u ) : ( v ) ) ;
        v =  ( ( ( ( ( ( r ) < ( s ) ) ? ( r ) : ( s ) ) ) < ( ( ( ( t ) < 
            ( u ) ) ? ( t ) : ( u ) ) ) ) ? ( ( ( ( r ) < ( s ) ) ? ( r ) : 
            ( s ) ) ) : ( ( ( ( t ) < ( u ) ) ? ( t ) : ( u ) ) ) ) ;
        z =  ( ( y ) < - 0.292893218813452476 ) ? ( - 2.0 * ( ( y ) + 1.0 ) *
             ( ( y ) + 1.0 ) ) : ( ( ( y ) <= 0 ) ? ( - 2.0 * ( y ) * 
             ( ( y ) + 2.0 ) ) : ( ( ( y ) < 0.292893218813452476 ) ?
             ( 2.0 * ( y ) * ( 2.0 - ( y ) ) ) : ( - 2.0 * ( 1.0 - ( y ) ) *
             ( 1.0 - ( y ) ) ) ) ) ;
# 20
        printf("No debuggin\n");
# 22
}
#ident "acomp: (CDS) SPARCompilers 2.0.1 03 Sep 1992"
runner% cc -o prepro prepro.c
runner% prepro
No debuggin
runner% prepro2     (Removes comment from around /*#define DEBUG */)
-0.000000
1, 1