sysdeps/ieee754/ldbl-128ibm/s_rintl.c

   1 /* Round to int long double floating-point values.
   2    IBM extended format long double version.
   3    Copyright (C) 2006 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 /* This has been coded in assembler because GCC makes such a mess of it
  22    when it's coded in C.  */
  23
  24 #include <math.h>
  25 #include <fenv_libc.h>
  26 #include <math_ldbl_opt.h>
  27 #include <float.h>
  28 #include <ieee754.h>
  29
  30
  31 #ifdef __STDC__
  32 long double
  33 __rintl (long double x)
  34 #else
  35 long double
  36 __rintl (x)
  37      long double x;
  38 #endif
  39 {
  40   double xh, xl, hi, lo;
  41
  42   ldbl_unpack (x, &xh, &xl);
  43
  44   /* Return Inf, Nan, +/-0 unchanged.  */
  45   if (__builtin_expect (xh != 0.0
  46                         && __builtin_isless (__builtin_fabs (xh),
  47                                              __builtin_inf ()), 1))
  48     {
  49       double orig_xh;
  50       int save_round = fegetround ();
  51
  52       /* Long double arithmetic, including the canonicalisation below,
  53          only works in round-to-nearest mode.  */
  54       fesetround (FE_TONEAREST);
  55
  56       /* Convert the high double to integer.  */
  57       orig_xh = xh;
  58       hi = ldbl_nearbyint (xh);
  59
  60       /* Subtract integral high part from the value.  If the low double
  61          happens to be exactly 0.5 or -0.5, you might think that this
  62          subtraction could result in an incorrect conversion.  For
  63          instance, subtracting an odd number would cause this function
  64          to round in the wrong direction.  However, if we have a
  65          canonical long double with the low double 0.5 or -0.5, then the
  66          high double must be even.  */
  67       xh -= hi;
  68       ldbl_canonicalize (&xh, &xl);
  69
  70       /* Now convert the low double, adjusted for any remainder from the
  71          high double.  */
  72       lo = ldbl_nearbyint (xh);
  73
  74       xh -= lo;
  75       ldbl_canonicalize (&xh, &xl);
  76
  77       switch (save_round)
  78         {
  79         case FE_TONEAREST:
  80           if (xl > 0.0 && xh == 0.5)
  81             lo += 1.0;
  82           else if (xl < 0.0 && -xh == 0.5)
  83             lo -= 1.0;
  84           break;
  85
  86         case FE_TOWARDZERO:
  87           if (orig_xh < 0.0)
  88             goto do_up;
  89           /* Fall thru */
  90
  91         case FE_DOWNWARD:
  92           if (xh < 0.0 || (xh == 0.0 && xl < 0.0))
  93             lo -= 1.0;
  94           break;
  95
  96         case FE_UPWARD:
  97         do_up:
  98           if (xh > 0.0 || (xh == 0.0 && xl > 0.0))
  99             lo += 1.0;
 100           break;
 101         }
 102
 103       /* Ensure the final value is canonical.  In certain cases,
 104          rounding causes hi,lo calculated so far to be non-canonical.  */
 105       xh = hi;
 106       xl = lo;
 107       ldbl_canonicalize (&xh, &xl);
 108
 109       /* Ensure we return -0 rather than +0 when appropriate.  */
 110       if (orig_xh < 0.0)
 111         xh = -__builtin_fabs (xh);
 112
 113       fesetround (save_round);
 114     }
 115
 116   return ldbl_pack (xh, xl);
 117 }
 118
 119 long_double_symbol (libm, __rintl, rintl);