Subversion Repositories planix.SVN

#include <math.h>
#include <errno.h>

/* modf suitable for IEEE double-precision */

#define MASK    0x7ffL
#define SIGN    0x80000000
#define SHIFT   20
#define BIAS    1022L

typedef union
{
        double  d;
        struct
        {
                long    ms;
                long    ls;
        } i;
} Cheat;

double
modf(double d, double *ip)
{
        Cheat x;
        int e;

        if(-1 < d && d < 1) {
                *ip = 0;
                return d;
        }
        x.d = d;
        x.i.ms &= ~SIGN;
        e = (x.i.ms >> SHIFT) & MASK;
        if(e == MASK || e == 0){
                errno = EDOM;
                *ip = (d > 0)? HUGE_VAL : -HUGE_VAL;
                return 0;
        }
        e -= BIAS;
        if(e <= SHIFT+1) {
                x.i.ms &= ~(0x1fffffL >> e);
                x.i.ls = 0;
        } else
        if(e <= SHIFT+33)
                x.i.ls &= ~(0x7fffffffL >> (e-SHIFT-2));
        if(d > 0){
                *ip = x.d;
                return d - x.d;
        }else{
                *ip = -x.d;
                return d + x.d;
        }
}