sysdeps/i386/setfpucw.c

   1 /* Set the FPU control word for x86.
   2    Copyright (C) 2003, 2004 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <math.h>
  21 #include <fpu_control.h>
  22 #include <fenv.h>
  23 #include <unistd.h>
  24 #include <ldsodefs.h>
  25 #include <dl-procinfo.h>
  26
  27 void
  28 __setfpucw (fpu_control_t set)
  29 {
  30   fpu_control_t cw;
  31
  32   /* Fetch the current control word.  */
  33   __asm__ ("fnstcw %0" : "=m" (*&cw));
  34
  35   /* Preserve the reserved bits, and set the rest as the user
  36      specified (or the default, if the user gave zero).  */
  37   cw &= _FPU_RESERVED;
  38   cw |= set & ~_FPU_RESERVED;
  39
  40   __asm__ ("fldcw %0" : : "m" (*&cw));
  41
  42   /* If the CPU supports SSE, we set the MXCSR as well.  */
  43   if ((GLRO(dl_hwcap) & HWCAP_I386_XMM) != 0)
  44     {
  45       unsigned int xnew_exc;
  46
  47       /* Get the current MXCSR.  */
  48       __asm__ ("stmxcsr %0" : "=m" (*&xnew_exc));
  49
  50       xnew_exc &= ~((0xc00 << 3) | (FE_ALL_EXCEPT << 7));
  51       xnew_exc |= ((set & 0xc00) << 3) | ((set & FE_ALL_EXCEPT) << 7);
  52
  53       __asm__ ("ldmxcsr %0" : : "m" (*&xnew_exc));
  54     }
  55 }