glibc/sysdeps/ieee754/dbl-64/s_nearbyint.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.
 * ====================================================
 */

/*
 * rint(x)
 * Return x rounded to integral value according to the prevailing
 * rounding mode.
 * Method:
 *	Using floating addition.
 * Exception:
 *	Inexact flag raised if x not equal to rint(x).
 */

#include <fenv.h>
#include <math.h>
#include <math-barriers.h>
#include <math_private.h>
#include <fenv_private.h>
#include <libm-alias-double.h>
#include <math-use-builtins.h>

double
__nearbyint (double x)
{
#if USE_NEARBYINT_BUILTIN
  return __builtin_nearbyint (x);
#else
  /* Use generic implementation.  */
  static const double
    TWO52[2] = {
		4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
		-4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  };
  fenv_t env;
  int64_t i0, sx;
  int32_t j0;
  EXTRACT_WORDS64 (i0, x);
  sx = (i0 >> 63) & 1;
  j0 = ((i0 >> 52) & 0x7ff) - 0x3ff;
  if (__glibc_likely (j0 < 52))
    {
      if (j0 < 0)
	{
	  libc_feholdexcept (&env);
	  double w = TWO52[sx] + math_opt_barrier (x);
	  double t =  w - TWO52[sx];
	  math_force_eval (t);
	  libc_fesetenv (&env);
	  return copysign (t, x);
	}
    }
  else
    {
      if (j0 == 0x400)
	return x + x;			/* inf or NaN  */
      else
	return x;			/* x is integral  */
    }
  libc_feholdexcept (&env);
  double w = TWO52[sx] + math_opt_barrier (x);
  double t = w - TWO52[sx];
  math_force_eval (t);
  libc_fesetenv (&env);
  return t;
#endif /* ! USE_NEARBYINT_BUILTIN  */
}
libm_alias_double (__nearbyint, nearbyint)