s_modf.c

Go to the documentation of this file.

/* @(#)s_modf.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/*
 * modf(double x, double *iptr) 
 * return fraction part of x, and return x's integral part in *iptr.
 * Method:
 *  Bit twiddling.
 *
 * Exception:
 *  No exception.
 */

#include "math.h"
#include "math_private.h"

static const double one = 1.0;

double
modf(double x, double *iptr)
{
    int32_t i0,i1,j0;
    u_int32_t i;
    EXTRACT_WORDS(i0,i1,x);
    j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
    if(j0<20) {         /* integer part in high x */
        if(j0<0) {          /* |x|<1 */
            INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
        return x;
        } else {
        i = (0x000fffff)>>j0;
        if(((i0&i)|i1)==0) {        /* x is integral */
            u_int32_t high;
            *iptr = x;
            GET_HIGH_WORD(high,x);
            INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
            return x;
        } else {
            INSERT_WORDS(*iptr,i0&(~i),0);
            return x - *iptr;
        }
        }
    } else if (j0>51) {     /* no fraction part */
        u_int32_t high;
        *iptr = x*one;
        GET_HIGH_WORD(high,x);
        INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
        return x;
    } else {            /* fraction part in low x */
        i = ((u_int32_t)(0xffffffff))>>(j0-20);
        if((i1&i)==0) {         /* x is integral */
            u_int32_t high;
        *iptr = x;
        GET_HIGH_WORD(high,x);
        INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
        return x;
        } else {
            INSERT_WORDS(*iptr,i0,i1&(~i));
        return x - *iptr;
        }
    }
}