sysdeps/ieee754/dbl-64/s_lround.c

   1 /* Round double value to long int.
   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 #include <fenv.h>
  20 #include <limits.h>
  21 #include <math.h>
  22
  23 #include <math_private.h>
  24 #include <libm-alias-double.h>
  25 #include <fix-fp-int-convert-overflow.h>
  26
  27 /* For LP64, lround is an alias for llround.  */
  28 #ifndef _LP64
  29
  30 long int
  31 __lround (double x)
  32 {
  33   int32_t j0;
  34   int64_t i0;
  35   long int result;
  36   int sign;
  37
  38   EXTRACT_WORDS64 (i0, x);
  39   j0 = ((i0 >> 52) & 0x7ff) - 0x3ff;
  40   sign = i0 < 0 ? -1 : 1;
  41   i0 &= UINT64_C(0xfffffffffffff);
  42   i0 |= UINT64_C(0x10000000000000);
  43
  44   if (j0 < (int32_t) (8 * sizeof (long int)) - 1)
  45     {
  46       if (j0 < 0)
  47         return j0 < -1 ? 0 : sign;
  48       else if (j0 >= 52)
  49         result = i0 << (j0 - 52);
  50       else
  51         {
  52           i0 += UINT64_C(0x8000000000000) >> j0;
  53
  54           result = i0 >> (52 - j0);
  55 #ifdef FE_INVALID
  56           if (sizeof (long int) == 4
  57               && sign == 1
  58               && result == LONG_MIN)
  59             /* Rounding brought the value out of range.  */
  60             feraiseexcept (FE_INVALID);
  61 #endif
  62         }
  63     }
  64   else
  65     {
  66       /* The number is too large.  Unless it rounds to LONG_MIN,
  67          FE_INVALID must be raised and the return value is
  68          unspecified.  */
  69 #ifdef FE_INVALID
  70       if (FIX_DBL_LONG_CONVERT_OVERFLOW
  71           && !(sign == -1
  72                && (sizeof (long int) == 4
  73                    ? x > (double) LONG_MIN - 0.5
  74                    : x >= (double) LONG_MIN)))
  75         {
  76           feraiseexcept (FE_INVALID);
  77           return sign == 1 ? LONG_MAX : LONG_MIN;
  78         }
  79       else if (!FIX_DBL_LONG_CONVERT_OVERFLOW
  80           && sizeof (long int) == 4
  81           && x <= (double) LONG_MIN - 0.5)
  82         {
  83           /* If truncation produces LONG_MIN, the cast will not raise
  84              the exception, but may raise "inexact".  */
  85           feraiseexcept (FE_INVALID);
  86           return LONG_MIN;
  87         }
  88 #endif
  89       return (long int) x;
  90     }
  91
  92   return sign * result;
  93 }
  94
  95 libm_alias_double (__lround, lround)
  96
  97 #endif