sysdeps/ieee754/dbl-64/s_trunc.c

   1 /* Truncate argument to nearest integral value not larger than the argument.
   2    Copyright (C) 1997-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   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, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #define NO_MATH_REDIRECT
  21 #include <math.h>
  22
  23 #include <math_private.h>
  24 #include <libm-alias-double.h>
  25
  26
  27 double
  28 __trunc (double x)
  29 {
  30   int64_t i0, j0;
  31   int64_t sx;
  32
  33   EXTRACT_WORDS64 (i0, x);
  34   sx = i0 & UINT64_C (0x8000000000000000);
  35   j0 = ((i0 >> 52) & 0x7ff) - 0x3ff;
  36   if (j0 < 52)
  37     {
  38       if (j0 < 0)
  39         /* The magnitude of the number is < 1 so the result is +-0.  */
  40         INSERT_WORDS64 (x, sx);
  41       else
  42         INSERT_WORDS64 (x, sx | (i0 & ~(UINT64_C (0x000fffffffffffff) >> j0)));
  43     }
  44   else
  45     {
  46       if (j0 == 0x400)
  47         /* x is inf or NaN.  */
  48         return x + x;
  49     }
  50
  51   return x;
  52 }
  53 #ifndef __trunc
  54 libm_alias_double (__trunc, trunc)
  55 #endif