1  /* Round to nearest integer.  PowerPC64 version.
       2     Copyright (C) 2019-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Library General Public License as
       7     published by the Free Software Foundation; either version 2 of the
       8     License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Library General Public License for more details.
      14  
      15     You should have received a copy of the GNU Library General Public
      16     License along with the GNU C Library; see the file COPYING.LIB.  If
      17     not, see <https://www.gnu.org/licenses/>.  */
      18  
      19  #define NO_MATH_REDIRECT
      20  #define lround __redirect_lround
      21  #define __lround __redirect___lround
      22  #include <math.h>
      23  #undef lround
      24  #undef __lround
      25  #include <libm-alias-double.h>
      26  #include <math-barriers.h>
      27  
      28  long long int
      29  __llround (double x)
      30  {
      31  #ifdef _ARCH_PWR5X
      32    double r = __builtin_round (x);
      33    /* Prevent gcc from calling llround directly when compiled with
      34       -fno-math-errno by inserting a barrier.  */
      35    math_opt_barrier (r);
      36    return r;
      37  #else
      38    /* IEEE 1003.1 llround function.  IEEE specifies "round to the nearest
      39       integer value, rounding halfway cases away from zero, regardless of
      40       the current rounding mode."  However PowerPC Architecture defines
      41       "round to Nearest" as "Choose the best approximation. In case of a
      42       tie, choose the one that is even (least significant bit o).".
      43       So we can't use the PowerPC "round to Nearest" mode. Instead we set
      44       "round toward Zero" mode and round by adding +-0.5 before rounding
      45       to the integer value.
      46  
      47       It is necessary to detect when x is (+-)0x1.fffffffffffffp-2
      48       because adding +-0.5 in this case will cause an erroneous shift,
      49       carry and round.  We simply return 0 if 0.5 > x > -0.5.  Likewise
      50       if x is and odd number between +-(2^52 and 2^53-1) a shift and
      51       carry will erroneously round if biased with +-0.5.  Therefore if x
      52       is greater/less than +-2^52 we don't need to bias the number with
      53       +-0.5.  */
      54  
      55    double ax = fabs (x);
      56  
      57    if (ax < 0.5)
      58      return 0;
      59  
      60    if (ax < 0x1p+52)
      61      {
      62        /* Test whether an integer to avoid spurious "inexact".  */
      63        double t = ax + 0x1p+52;
      64        t = t - 0x1p+52;
      65        if (ax != t)
      66  	{
      67  	  ax = ax + 0.5;
      68  	  if (x < 0.0)
      69  	    ax = -fabs (ax);
      70  	  x = ax;
      71  	}
      72      }
      73  
      74    long int ret;
      75    __asm__ ("fctidz %0, %1" : "=d" (ret) : "d" (x));
      76    return ret;
      77  #endif
      78  }
      79  #ifndef __llround
      80  strong_alias (__llround, __lround)
      81  libm_alias_double (__llround, llround)
      82  libm_alias_double (__lround, lround)
      83  #endif