glibc/sysdeps/ieee754/dbl-64/s_modf.c

/*
 * ====================================================
 * 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>
#include <libm-alias-double.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 */
	    {
	      *iptr = x;
	      INSERT_WORDS (x, i0 & 0x80000000, 0);     /* return +-0 */
	      return x;
	    }
	  else
	    {
	      INSERT_WORDS (*iptr, i0 & (~i), 0);
	      return x - *iptr;
	    }
	}
    }
  else if (__glibc_unlikely (j0 > 51))              /* no fraction part */
    {
      *iptr = x * one;
      /* We must handle NaNs separately.  */
      if (j0 == 0x400 && ((i0 & 0xfffff) | i1))
	return x * one;
      INSERT_WORDS (x, i0 & 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 */
	{
	  *iptr = x;
	  INSERT_WORDS (x, i0 & 0x80000000, 0);         /* return +-0 */
	  return x;
	}
      else
	{
	  INSERT_WORDS (*iptr, i0, i1 & (~i));
	  return x - *iptr;
	}
    }
}
#ifndef __modf
libm_alias_double (__modf, modf)
#endif