xref: /freebsd/lib/libc/gen/modf.c (revision dc36d6f9bb1753f3808552f3afd30eda9a7b206a)

/*
 * ====================================================
 * 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 <sys/types.h>
#include <machine/endian.h>
#include <math.h>

/* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */

#if BYTE_ORDER == BIG_ENDIAN

typedef union
{
  double value;
  struct
  {
    u_int32_t msw;
    u_int32_t lsw;
  } parts;
} ieee_double_shape_type;

#endif

#if BYTE_ORDER == LITTLE_ENDIAN

typedef union
{
  double value;
  struct
  {
    u_int32_t lsw;
    u_int32_t msw;
  } parts;
} 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)

/* 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)

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;
	    if (j0 == 0x400) {		/* inf/NaN */
		*iptr = x;
		return 0.0 / x;
	    }
	    *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;
	    }
	}
}