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glibc  2.9
setfpucw.c
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00001 /* Set the FPU control word for x86.
00002    Copyright (C) 2003, 2004 Free Software Foundation, Inc.
00003    This file is part of the GNU C Library.
00004 
00005    The GNU C Library is free software; you can redistribute it and/or
00006    modify it under the terms of the GNU Lesser General Public
00007    License as published by the Free Software Foundation; either
00008    version 2.1 of the License, or (at your option) any later version.
00009 
00010    The GNU C Library is distributed in the hope that it will be useful,
00011    but WITHOUT ANY WARRANTY; without even the implied warranty of
00012    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00013    Lesser General Public License for more details.
00014 
00015    You should have received a copy of the GNU Lesser General Public
00016    License along with the GNU C Library; if not, write to the Free
00017    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00018    02111-1307 USA.  */
00019 
00020 #include <math.h>
00021 #include <fpu_control.h>
00022 #include <fenv.h>
00023 #include <unistd.h>
00024 #include <ldsodefs.h>
00025 #include <dl-procinfo.h>
00026 
00027 void
00028 __setfpucw (fpu_control_t set)
00029 {
00030   fpu_control_t cw;
00031 
00032   /* Fetch the current control word.  */
00033   __asm__ ("fnstcw %0" : "=m" (*&cw));
00034 
00035   /* Preserve the reserved bits, and set the rest as the user
00036      specified (or the default, if the user gave zero).  */
00037   cw &= _FPU_RESERVED;
00038   cw |= set & ~_FPU_RESERVED;
00039 
00040   __asm__ ("fldcw %0" : : "m" (*&cw));
00041 
00042   /* If the CPU supports SSE, we set the MXCSR as well.  */
00043   if ((GLRO(dl_hwcap) & HWCAP_I386_XMM) != 0)
00044     {
00045       unsigned int xnew_exc;
00046 
00047       /* Get the current MXCSR.  */
00048       __asm__ ("stmxcsr %0" : "=m" (*&xnew_exc));
00049 
00050       xnew_exc &= ~((0xc00 << 3) | (FE_ALL_EXCEPT << 7));
00051       xnew_exc |= ((set & 0xc00) << 3) | ((set & FE_ALL_EXCEPT) << 7);
00052 
00053       __asm__ ("ldmxcsr %0" : : "m" (*&xnew_exc));
00054     }
00055 }