libm/i386/fesetround.c

   1 /* Set current rounding direction.
   2    Copyright (C) 1997, 2003, 2004, 2005 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <fenv.h>
  21 #include <unistd.h>
  22
  23 int
  24 fesetround (int round)
  25 {
  26   unsigned short int cw;
  27
  28   if ((round & ~0xc00) != 0)
  29     /* ROUND is no valid rounding mode.  */
  30     return 1;
  31
  32   __asm__ ("fnstcw %0" : "=m" (*&cw));
  33   cw &= ~0xc00;
  34   cw |= round;
  35   __asm__ ("fldcw %0" : : "m" (*&cw));
  36
  37 #if 0
  38   /* If the CPU supports SSE we set the MXCSR as well.  */
  39   if ((GLRO(dl_hwcap) & HWCAP_I386_XMM) != 0)
  40     {
  41       unsigned int xcw;
  42
  43       __asm__ ("stmxcsr %0" : "=m" (*&xcw));
  44       xcw &= ~0x6000;
  45       xcw |= round << 3;
  46       __asm__ ("ldmxcsr %0" : : "m" (*&xcw));
  47     }
  48 #endif
  49
  50   return 0;
  51 }