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

   1 /* Round to int long double floating-point values.
   2    IBM extended format long double version.
   3    Copyright (C) 2006, 2007 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 <math_ldbl_opt.h>
  26 #include <float.h>
  27 #include <ieee754.h>
  28
  29
  30 #ifdef __STDC__
  31 long double
  32 __roundl (long double x)
  33 #else
  34 long double
  35 __roundl (x)
  36      long double x;
  37 #endif
  38 {
  39   double xh, xl, hi, lo;
  40
  41   ldbl_unpack (x, &xh, &xl);
  42
  43   /* Return Inf, Nan, +/-0 unchanged.  */
  44   if (__builtin_expect (xh != 0.0
  45                         && __builtin_isless (__builtin_fabs (xh),
  46                                              __builtin_inf ()), 1))
  47     {
  48       double orig_xh;
  49
  50       /* Long double arithmetic, including the canonicalisation below,
  51          only works in round-to-nearest mode.  */
  52
  53       /* Convert the high double to integer.  */
  54       orig_xh = xh;
  55       hi = ldbl_nearbyint (xh);
  56
  57       /* Subtract integral high part from the value.  */
  58       xh -= hi;
  59       ldbl_canonicalize (&xh, &xl);
  60
  61       /* Now convert the low double, adjusted for any remainder from the
  62          high double.  */
  63       lo = ldbl_nearbyint (xh);
  64
  65       /* Adjust the result when the remainder is exactly 0.5.  nearbyint
  66          rounds values halfway between integers to the nearest even
  67          integer.  roundl must round away from zero.
  68          Also correct cases where nearbyint returns an incorrect value
  69          for LO.  */
  70       xh -= lo;
  71       ldbl_canonicalize (&xh, &xl);
  72       if (xh == 0.5)
  73         {
  74           if (xl > 0.0 || (xl == 0.0 && orig_xh > 0.0))
  75             lo += 1.0;
  76         }
  77       else if (-xh == 0.5)
  78         {
  79           if (xl < 0.0 || (xl == 0.0 && orig_xh < 0.0))
  80             lo -= 1.0;
  81         }
  82
  83       /* Ensure the final value is canonical.  In certain cases,
  84          rounding causes hi,lo calculated so far to be non-canonical.  */
  85       xh = hi;
  86       xl = lo;
  87       ldbl_canonicalize (&xh, &xl);
  88     }
  89
  90   return ldbl_pack (xh, xl);
  91 }
  92
  93 long_double_symbol (libm, __roundl, roundl);