sysdeps/powerpc/powerpc32/fpu/s_lround.c

   1 /* lround function.  PowerPC32 version.
   2    Copyright (C) 2004-2019 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #define lroundf __redirect_lroundf
  20 #define __lroundf __redirect___lroundf
  21 #include <math.h>
  22 #undef lroundf
  23 #undef __lroundf
  24 #include <libm-alias-float.h>
  25 #include <libm-alias-double.h>
  26
  27 long int
  28 __lround (double x)
  29 {
  30 #ifdef _ARCH_PWR5X
  31   x = round (x);
  32 #else
  33   /* Ieee 1003.1 lround function.  ieee specifies "round to the nearest
  34      integer value, rounding halfway cases away from zero, regardless of
  35      the current rounding mode."  however powerpc architecture defines
  36      "round to nearest" as "choose the best approximation. in case of a
  37      tie, choose the one that is even (least significant bit o).".
  38      so we can't use the powerpc "round to nearest" mode. instead we set
  39      "round toward zero" mode and round by adding +-0.5 before rounding
  40      to the integer value.  it is necessary to detect when x is
  41      (+-)0x1.fffffffffffffp-2 because adding +-0.5 in this case will
  42      cause an erroneous shift, carry and round.  we simply return 0 if
  43      0.5 > x > -0.5.  */
  44
  45   double ax = fabs (x);
  46
  47   if (ax < 0.5)
  48     return 0;
  49
  50   if (x >= 0x7fffffff.8p0 || x <= -0x80000000.8p0)
  51     x = (x < 0.0) ? -0x1p+52 : 0x1p+52;
  52   else
  53     {
  54       /* Test whether an integer to avoid spurious "inexact".  */
  55       double t = ax + 0x1p+52;
  56       t = t - 0x1p+52;
  57       if (ax != t)
  58         {
  59           ax = ax + 0.5;
  60           if (x < 0.0)
  61             ax = -fabs (ax);
  62           x = ax;
  63         }
  64     }
  65 #endif
  66   /* Force evaluation of values larger than long int, so invalid
  67      exceptions are raise.  */
  68   long long int ret;
  69   asm ("fctiwz %0, %1" : "=d" (ret) : "d" (x));
  70   return ret;
  71 }
  72 #ifndef __lround
  73 libm_alias_double (__lround, lround)
  74
  75 strong_alias (__lround, __lroundf)
  76 libm_alias_float (__lround, lround)
  77 #endif