1  /* Set the FPU control word for x86.
       2     Copyright (C) 2003-2023 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     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <math.h>
      20  #include <fpu_control.h>
      21  #include <fenv.h>
      22  #include <unistd.h>
      23  #include <ldsodefs.h>
      24  #include <dl-procinfo.h>
      25  
      26  void
      27  __setfpucw (fpu_control_t set)
      28  {
      29    fpu_control_t cw;
      30  
      31    /* Fetch the current control word.  */
      32    __asm__ ("fnstcw %0" : "=m" (*&cw));
      33  
      34    /* Preserve the reserved bits, and set the rest as the user
      35       specified (or the default, if the user gave zero).  */
      36    cw &= _FPU_RESERVED;
      37    cw |= set & ~_FPU_RESERVED;
      38  
      39    __asm__ ("fldcw %0" : : "m" (*&cw));
      40  
      41    /* If the CPU supports SSE, we set the MXCSR as well.  */
      42    if (CPU_FEATURE_USABLE (SSE))
      43      {
      44        unsigned int xnew_exc;
      45  
      46        /* Get the current MXCSR.  */
      47        __asm__ ("stmxcsr %0" : "=m" (*&xnew_exc));
      48  
      49        xnew_exc &= ~((0xc00 << 3) | (FE_ALL_EXCEPT << 7));
      50        xnew_exc |= ((set & 0xc00) << 3) | ((set & FE_ALL_EXCEPT) << 7);
      51  
      52        __asm__ ("ldmxcsr %0" : : "m" (*&xnew_exc));
      53      }
      54  }