sysdeps/ieee754/dbl-64/s_round.c

   1 /* Round double to integer away from zero.
   2    Copyright (C) 1997-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #define NO_MATH_REDIRECT
  20 #include <math.h>
  21
  22 #include <math_private.h>
  23 #include <libm-alias-double.h>
  24 #include <stdint.h>
  25 #include <math-use-builtins.h>
  26
  27
  28 double
  29 __round (double x)
  30 {
  31 #if USE_ROUND_BUILTIN
  32   return __builtin_round (x);
  33 #else
  34   /* Use generic implementation.  */
  35   int64_t i0, j0;
  36
  37   EXTRACT_WORDS64 (i0, x);
  38   j0 = ((i0 >> 52) & 0x7ff) - 0x3ff;
  39   if (__glibc_likely (j0 < 52))
  40     {
  41       if (j0 < 0)
  42         {
  43           i0 &= UINT64_C (0x8000000000000000);
  44           if (j0 == -1)
  45             i0 |= UINT64_C (0x3ff0000000000000);
  46         }
  47       else
  48         {
  49           uint64_t i = UINT64_C (0x000fffffffffffff) >> j0;
  50           if ((i0 & i) == 0)
  51             /* X is integral.  */
  52             return x;
  53
  54           i0 += UINT64_C (0x0008000000000000) >> j0;
  55           i0 &= ~i;
  56         }
  57     }
  58   else
  59     {
  60       if (j0 == 0x400)
  61         /* Inf or NaN.  */
  62         return x + x;
  63       else
  64         return x;
  65     }
  66
  67   INSERT_WORDS64 (x, i0);
  68   return x;
  69 #endif /* ! USE_ROUND_BUILTIN  */
  70 }
  71 libm_alias_double (__round, round)