1  /*
       2   * ====================================================
       3   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
       4   *
       5   * Developed at SunPro, a Sun Microsystems, Inc. business.
       6   * Permission to use, copy, modify, and distribute this
       7   * software is freely granted, provided that this notice
       8   * is preserved.
       9   * ====================================================
      10   */
      11  
      12  /*
      13   * rint(x)
      14   * Return x rounded to integral value according to the prevailing
      15   * rounding mode.
      16   * Method:
      17   *	Using floating addition.
      18   * Exception:
      19   *	Inexact flag raised if x not equal to rint(x).
      20   */
      21  
      22  #include <fenv.h>
      23  #include <math.h>
      24  #include <math-barriers.h>
      25  #include <math_private.h>
      26  #include <fenv_private.h>
      27  #include <libm-alias-double.h>
      28  #include <math-use-builtins.h>
      29  
      30  double
      31  __nearbyint (double x)
      32  {
      33  #if USE_NEARBYINT_BUILTIN
      34    return __builtin_nearbyint (x);
      35  #else
      36    /* Use generic implementation.  */
      37    static const double
      38      TWO52[2] = {
      39  		4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
      40  		-4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
      41    };
      42    fenv_t env;
      43    int64_t i0, sx;
      44    int32_t j0;
      45    EXTRACT_WORDS64 (i0, x);
      46    sx = (i0 >> 63) & 1;
      47    j0 = ((i0 >> 52) & 0x7ff) - 0x3ff;
      48    if (__glibc_likely (j0 < 52))
      49      {
      50        if (j0 < 0)
      51  	{
      52  	  libc_feholdexcept (&env);
      53  	  double w = TWO52[sx] + math_opt_barrier (x);
      54  	  double t =  w - TWO52[sx];
      55  	  math_force_eval (t);
      56  	  libc_fesetenv (&env);
      57  	  return copysign (t, x);
      58  	}
      59      }
      60    else
      61      {
      62        if (j0 == 0x400)
      63  	return x + x;			/* inf or NaN  */
      64        else
      65  	return x;			/* x is integral  */
      66      }
      67    libc_feholdexcept (&env);
      68    double w = TWO52[sx] + math_opt_barrier (x);
      69    double t = w - TWO52[sx];
      70    math_force_eval (t);
      71    libc_fesetenv (&env);
      72    return t;
      73  #endif /* ! USE_NEARBYINT_BUILTIN  */
      74  }
      75  libm_alias_double (__nearbyint, nearbyint)