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, 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 __truncl (long double x)
  33 #else
  34 long double
  35 __truncl (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 non-zero.  nearbyint
  66          rounds values to the nearest integer, and values halfway
  67          between integers to the nearest even integer.  floorl must
  68          round towards -Inf.  */
  69       xh -= lo;
  70       ldbl_canonicalize (&xh, &xl);
  71
  72       if (orig_xh < 0.0)
  73         {
  74           if (xh > 0.0 || (xh == 0.0 && xl > 0.0))
  75             lo += 1.0;
  76         }
  77       else
  78         {
  79           if (xh < 0.0 || (xh == 0.0 && xl < 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       /* Ensure we return -0 rather than +0 when appropriate.  */
  90       if (orig_xh < 0.0)
  91         xh = -__builtin_fabs (xh);
  92     }
  93
  94   return ldbl_pack (xh, xl);
  95 }
  96
  97 long_double_symbol (libm, __truncl, truncl);