sysdeps/x86_64/fpu/fesetround.c

   1 /* Set current rounding direction.
   2    Copyright (C) 2001-2015 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 <fenv.h>
  20
  21 int
  22 __fesetround (int round)
  23 {
  24   unsigned short int cw;
  25   int mxcsr;
  26
  27   if ((round & ~0xc00) != 0)
  28     /* ROUND is no valid rounding mode.  */
  29     return 1;
  30
  31   /* First set the x87 FPU.  */
  32   asm ("fnstcw %0" : "=m" (*&cw));
  33   cw &= ~0xc00;
  34   cw |= round;
  35   asm ("fldcw %0" : : "m" (*&cw));
  36
  37   /* And now the MSCSR register for SSE, the precision is at different bit
  38      positions in the different units, we need to shift it 3 bits.  */
  39   asm ("stmxcsr %0" : "=m" (*&mxcsr));
  40   mxcsr &= ~ 0x6000;
  41   mxcsr |= round << 3;
  42   asm ("ldmxcsr %0" : : "m" (*&mxcsr));
  43
  44   return 0;
  45 }
  46 libm_hidden_def (__fesetround)
  47 weak_alias (__fesetround, fesetround)
  48 libm_hidden_weak (fesetround)