musl/src/math/s_modf.c

/* @(#)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;
        uint32_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 */
                    uint32_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 */
            uint32_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 = ((uint32_t)(0xffffffff))>>(j0-20);
            if((i1&i)==0) {             /* x is integral */
                uint32_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;
            }
        }
}