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

   1 /* Truncate (toward zero) 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 __truncl (long double x)
  34 #else
  35 long double
  36 __truncl (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.  */
  61       xh -= hi;
  62       ldbl_canonicalize (&xh, &xl);
  63
  64       /* Now convert the low double, adjusted for any remainder from the
  65          high double.  */
  66       lo = ldbl_nearbyint (xh);
  67
  68       /* Adjust the result when the remainder is non-zero.  nearbyint
  69          rounds values to the nearest integer, and values halfway
  70          between integers to the nearest even integer.  floorl must
  71          round towards -Inf.  */
  72       xh -= lo;
  73       ldbl_canonicalize (&xh, &xl);
  74
  75       if (orig_xh < 0.0)
  76         {
  77           if (xh > 0.0 || (xh == 0.0 && xl > 0.0))
  78             lo += 1.0;
  79         }
  80       else
  81         {
  82           if (xh < 0.0 || (xh == 0.0 && xl < 0.0))
  83             lo -= 1.0;
  84         }
  85
  86       /* Ensure the final value is canonical.  In certain cases,
  87          rounding causes hi,lo calculated so far to be non-canonical.  */
  88       xh = hi;
  89       xl = lo;
  90       ldbl_canonicalize (&xh, &xl);
  91
  92       /* Ensure we return -0 rather than +0 when appropriate.  */
  93       if (orig_xh < 0.0)
  94         xh = -__builtin_fabs (xh);
  95
  96       fesetround (save_round);
  97     }
  98
  99   return ldbl_pack (xh, xl);
 100 }
 101
 102 long_double_symbol (libm, __truncl, truncl);