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glibc  2.9
fesetround.c
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00001 /* Set current rounding direction.
00002    Copyright (C) 1997, 2003, 2004, 2005 Free Software Foundation, Inc.
00003    This file is part of the GNU C Library.
00004    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
00005 
00006    The GNU C Library is free software; you can redistribute it and/or
00007    modify it under the terms of the GNU Lesser General Public
00008    License as published by the Free Software Foundation; either
00009    version 2.1 of the License, or (at your option) any later version.
00010 
00011    The GNU C Library is distributed in the hope that it will be useful,
00012    but WITHOUT ANY WARRANTY; without even the implied warranty of
00013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014    Lesser General Public License for more details.
00015 
00016    You should have received a copy of the GNU Lesser General Public
00017    License along with the GNU C Library; if not, write to the Free
00018    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00019    02111-1307 USA.  */
00020 
00021 #include <fenv.h>
00022 #include <unistd.h>
00023 #include <ldsodefs.h>
00024 #include <dl-procinfo.h>
00025 
00026 int
00027 fesetround (int round)
00028 {
00029   unsigned short int cw;
00030 
00031   if ((round & ~0xc00) != 0)
00032     /* ROUND is no valid rounding mode.  */
00033     return 1;
00034 
00035   __asm__ ("fnstcw %0" : "=m" (*&cw));
00036   cw &= ~0xc00;
00037   cw |= round;
00038   __asm__ ("fldcw %0" : : "m" (*&cw));
00039 
00040   /* If the CPU supports SSE we set the MXCSR as well.  */
00041   if ((GLRO(dl_hwcap) & HWCAP_I386_XMM) != 0)
00042     {
00043       unsigned int xcw;
00044 
00045       __asm__ ("stmxcsr %0" : "=m" (*&xcw));
00046       xcw &= ~0x6000;
00047       xcw |= round << 3;
00048       __asm__ ("ldmxcsr %0" : : "m" (*&xcw));
00049     }
00050 
00051   return 0;
00052 }
00053 libm_hidden_def (fesetround)