glibc/sysdeps/i386/fpu/fesetround.c

/* Set current rounding direction.
   Copyright (C) 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <fenv.h>

int
fesetround (int round)
{
  unsigned short int cw;

  if ((round & ~0xc00) != 0)
    /* ROUND is no valid rounding mode.  */
    return 0;

  __asm__ ("fnstcw %0" : "=m" (*&cw));
  cw &= ~0xc00;
  cw |= round;
  __asm__ ("fldcw %0" : : "m" (*&cw));

  return 1;
}