sysdeps/i386/fpu/fesetexcept.c

   1 /* Set given exception flags.  i386 version.
   2    Copyright (C) 2016-2023 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 <ldsodefs.h>
  21
  22 int
  23 fesetexcept (int excepts)
  24 {
  25   /* The flags can be set in the 387 unit or in the SSE unit.  To set a flag,
  26      it is sufficient to do it in the SSE unit, because that is guaranteed to
  27      not trap.  However, on i386 CPUs that have only a 387 unit, set the flags
  28      in the 387, as long as this cannot trap.  */
  29
  30   excepts &= FE_ALL_EXCEPT;
  31
  32   if (CPU_FEATURE_USABLE (SSE))
  33     {
  34       /* Get the control word of the SSE unit.  */
  35       unsigned int mxcsr;
  36       __asm__ ("stmxcsr %0" : "=m" (*&mxcsr));
  37
  38       /* Set relevant flags.  */
  39       mxcsr |= excepts;
  40
  41       /* Put the new data in effect.  */
  42       __asm__ ("ldmxcsr %0" : : "m" (*&mxcsr));
  43     }
  44   else
  45     {
  46       fenv_t temp;
  47
  48       /* Note: fnstenv masks all floating-point exceptions until the fldenv
  49          or fldcw below.  */
  50       __asm__ ("fnstenv %0" : "=m" (*&temp));
  51
  52       /* Set relevant flags.  */
  53       temp.__status_word |= excepts;
  54
  55       if ((~temp.__control_word) & excepts)
  56         {
  57           /* Setting the exception flags may trigger a trap (at the next
  58              floating-point instruction, but that does not matter).
  59              ISO C23 (7.6.4.4) does not allow it.  */
  60           __asm__ volatile ("fldcw %0" : : "m" (*&temp.__control_word));
  61           return -1;
  62         }
  63
  64       /* Store the new status word (along with the rest of the environment).  */
  65       __asm__ ("fldenv %0" : : "m" (*&temp));
  66     }
  67
  68   return 0;
  69 }