s_modf.c

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/* @(#)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.
 * ====================================================
 */

/*
FUNCTION
       <<modf>>, <<modff>>---split fractional and integer parts

INDEX
    modf
INDEX
    modff

ANSI_SYNOPSIS
    #include <math.h>
    double modf(double <[val]>, double *<[ipart]>);
        float modff(float <[val]>, float *<[ipart]>);

TRAD_SYNOPSIS
    #include <math.h>
    double modf(<[val]>, <[ipart]>)
        double <[val]>;
        double *<[ipart]>;

    float modff(<[val]>, <[ipart]>)
    float <[val]>;
        float *<[ipart]>;

DESCRIPTION
    <<modf>> splits the double <[val]> apart into an integer part
    and a fractional part, returning the fractional part and
    storing the integer part in <<*<[ipart]>>>.  No rounding
    whatsoever is done; the sum of the integer and fractional
    parts is guaranteed to be exactly  equal to <[val]>.   That
    is, if . <[realpart]> = modf(<[val]>, &<[intpart]>); then
    `<<<[realpart]>+<[intpart]>>>' is the same as <[val]>.
    <<modff>> is identical, save that it takes and returns
    <<float>> rather than <<double>> values.

RETURNS
    The fractional part is returned.  Each result has the same
    sign as the supplied argument <[val]>.

PORTABILITY
    <<modf>> is ANSI C. <<modff>> is an extension.

QUICKREF
    modf  ansi pure
    modff - pure

*/

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


static const double one = 1.0;

#define __int32_t long
#define __uint32_t unsigned long
#define __IEEE_LITTLE_ENDIAN

#ifdef __IEEE_BIG_ENDIAN

typedef union
{
  struct
  {
    __uint32_t msw;
    __uint32_t lsw;
  } parts;
  double value;
} ieee_double_shape_type;

#endif

#ifdef __IEEE_LITTLE_ENDIAN

typedef union
{
  struct
  {
    __uint32_t lsw;
    __uint32_t msw;
  } parts;
  double value;
} ieee_double_shape_type;

#endif


/* Get two 32 bit ints from a double.  */

#define EXTRACT_WORDS(ix0,ix1,d)                \
do {                                \
  ieee_double_shape_type ew_u;                  \
  ew_u.value = (d);                     \
  (ix0) = ew_u.parts.msw;                   \
  (ix1) = ew_u.parts.lsw;                   \
} while (0)

/* Get the more significant 32 bit int from a double.  */

#define GET_HIGH_WORD(i,d)                  \
do {                                \
  ieee_double_shape_type gh_u;                  \
  gh_u.value = (d);                     \
  (i) = gh_u.parts.msw;                     \
} while (0)

/* Get the less significant 32 bit int from a double.  */

#define GET_LOW_WORD(i,d)                   \
do {                                \
  ieee_double_shape_type gl_u;                  \
  gl_u.value = (d);                     \
  (i) = gl_u.parts.lsw;                     \
} while (0)

/* Set a double from two 32 bit ints.  */

#define INSERT_WORDS(d,ix0,ix1)                 \
do {                                \
  ieee_double_shape_type iw_u;                  \
  iw_u.parts.msw = (ix0);                   \
  iw_u.parts.lsw = (ix1);                   \
  (d) = iw_u.value;                     \
} while (0)




double modf(double x, double *iptr)
{
    __int32_t i0,i1,j_0;
    __uint32_t i;
    EXTRACT_WORDS(i0,i1,x);
    j_0 = ((i0>>20)&0x7ff)-0x3ff;   /* exponent of x */
    if(j_0<20) {            /* integer part in high x */
        if(j_0<0) {         /* |x|<1 */
            INSERT_WORDS(*iptr,i0&0x80000000U,0);   /* *iptr = +-0 */
        return x;
        } else {
        i = (0x000fffff)>>j_0;
        if(((i0&i)|i1)==0) {        /* x is integral */
            __uint32_t high;
            *iptr = x;
            GET_HIGH_WORD(high,x);
            INSERT_WORDS(x,high&0x80000000U,0); /* return +-0 */
            return x;
        } else {
            INSERT_WORDS(*iptr,i0&(~i),0);
            return x - *iptr;
        }
        }
    } else if (j_0>51) {        /* no fraction part */
        __uint32_t high;
        *iptr = x*one;
        GET_HIGH_WORD(high,x);
        INSERT_WORDS(x,high&0x80000000U,0); /* return +-0 */
        return x;
    } else {            /* fraction part in low x */
        i = ((__uint32_t)(0xffffffffU))>>(j_0-20);
        if((i1&i)==0) {         /* x is integral */
            __uint32_t high;
        *iptr = x;
        GET_HIGH_WORD(high,x);
        INSERT_WORDS(x,high&0x80000000U,0); /* return +-0 */
        return x;
        } else {
            INSERT_WORDS(*iptr,i0,i1&(~i));
        return x - *iptr;
        }
    }
}

//#endif /* _DOUBLE_IS_32BITS */