sysdeps/i386/setfpucw.c

   1 /* Set the FPU control word for x86.
   2    Copyright (C) 2003-2019 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    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <math.h>
  20 #include <fpu_control.h>
  21 #include <fenv.h>
  22 #include <unistd.h>
  23 #include <ldsodefs.h>
  24 #include <dl-procinfo.h>
  25
  26 void
  27 __setfpucw (fpu_control_t set)
  28 {
  29   fpu_control_t cw;
  30
  31   /* Fetch the current control word.  */
  32   __asm__ ("fnstcw %0" : "=m" (*&cw));
  33
  34   /* Preserve the reserved bits, and set the rest as the user
  35      specified (or the default, if the user gave zero).  */
  36   cw &= _FPU_RESERVED;
  37   cw |= set & ~_FPU_RESERVED;
  38
  39   __asm__ ("fldcw %0" : : "m" (*&cw));
  40
  41   /* If the CPU supports SSE, we set the MXCSR as well.  */
  42   if (HAS_CPU_FEATURE (SSE))
  43     {
  44       unsigned int xnew_exc;
  45
  46       /* Get the current MXCSR.  */
  47       __asm__ ("stmxcsr %0" : "=m" (*&xnew_exc));
  48
  49       xnew_exc &= ~((0xc00 << 3) | (FE_ALL_EXCEPT << 7));
  50       xnew_exc |= ((set & 0xc00) << 3) | ((set & FE_ALL_EXCEPT) << 7);
  51
  52       __asm__ ("ldmxcsr %0" : : "m" (*&xnew_exc));
  53     }
  54 }