sysdeps/x86_64/fpu/fesetround.c

   1 /* Set current rounding direction.
   2    Copyright (C) 2001, 2005 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 <fenv.h>
  21
  22 int
  23 fesetround (int round)
  24 {
  25   unsigned short int cw;
  26   int mxcsr;
  27
  28   if ((round & ~0xc00) != 0)
  29     /* ROUND is no valid rounding mode.  */
  30     return 1;
  31
  32   /* First set the x87 FPU.  */
  33   asm ("fnstcw %0" : "=m" (*&cw));
  34   cw &= ~0xc00;
  35   cw |= round;
  36   asm ("fldcw %0" : : "m" (*&cw));
  37
  38   /* And now the MSCSR register for SSE, the precision is at different bit
  39      positions in the different units, we need to shift it 3 bits.  */
  40   asm ("stmxcsr %0" : "=m" (*&mxcsr));
  41   mxcsr &= ~ 0x6000;
  42   mxcsr |= round << 3;
  43   asm ("ldmxcsr %0" : : "m" (*&mxcsr));
  44
  45   return 0;
  46 }
  47 libm_hidden_def (fesetround)