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  1. /*
  2.  * Copyright (C) 2005-2015 Free Software Foundation, Inc.
  3.  *
  4.  * This file is free software; you can redistribute it and/or modify it
  5.  * under the terms of the GNU General Public License as published by the
  6.  * Free Software Foundation; either version 3, or (at your option) any
  7.  * later version.
  8.  *
  9.  * This file is distributed in the hope that it will be useful, but
  10.  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12.  * General Public License for more details.
  13.  *
  14.  * Under Section 7 of GPL version 3, you are granted additional
  15.  * permissions described in the GCC Runtime Library Exception, version
  16.  * 3.1, as published by the Free Software Foundation.
  17.  *
  18.  * You should have received a copy of the GNU General Public License and
  19.  * a copy of the GCC Runtime Library Exception along with this program;
  20.  * see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  21.  * <http://www.gnu.org/licenses/>.
  22.  */
  23.  
  24. #ifndef _SOFT_FLOAT
  25. #define MXCSR_DAZ (1 << 6)      /* Enable denormals are zero mode */
  26. #define MXCSR_FTZ (1 << 15)     /* Enable flush to zero mode */
  27.  
  28. #ifndef __x86_64__
  29. /* All 64-bit targets have SSE and DAZ;
  30.    only check them explicitly for 32-bit ones. */
  31. #include "cpuid.h"
  32. #endif
  33.  
  34. static void __attribute__((constructor))
  35. #ifndef __x86_64__
  36. /* The i386 ABI only requires 4-byte stack alignment, so this is necessary
  37.    to make sure the fxsave struct gets correct alignment.
  38.    See PR27537 and PR28621.  */
  39. __attribute__ ((force_align_arg_pointer))
  40. #endif
  41. set_fast_math (void)
  42. {
  43. #ifndef __x86_64__
  44.   unsigned int eax, ebx, ecx, edx;
  45.  
  46.   if (!__get_cpuid (1, &eax, &ebx, &ecx, &edx))
  47.     return;
  48.  
  49.   if (edx & bit_SSE)
  50.     {
  51.       unsigned int mxcsr;
  52.  
  53.       if (edx & bit_FXSAVE)
  54.         {
  55.           /* Check if DAZ is available.  */
  56.           struct
  57.             {
  58.               unsigned short cwd;
  59.               unsigned short swd;
  60.               unsigned short twd;
  61.               unsigned short fop;
  62.               unsigned int fip;
  63.               unsigned int fcs;
  64.               unsigned int foo;
  65.               unsigned int fos;
  66.               unsigned int mxcsr;
  67.               unsigned int mxcsr_mask;
  68.               unsigned int st_space[32];
  69.               unsigned int xmm_space[32];
  70.               unsigned int padding[56];
  71.             } __attribute__ ((aligned (16))) fxsave;
  72.  
  73.           /* This is necessary since some implementations of FXSAVE
  74.              do not modify reserved areas within the image.  */
  75.           fxsave.mxcsr_mask = 0;
  76.  
  77.           __builtin_ia32_fxsave (&fxsave);
  78.  
  79.           mxcsr = fxsave.mxcsr;
  80.  
  81.           if (fxsave.mxcsr_mask & MXCSR_DAZ)
  82.             mxcsr |= MXCSR_DAZ;
  83.         }
  84.       else
  85.         mxcsr = __builtin_ia32_stmxcsr ();
  86.  
  87.       mxcsr |= MXCSR_FTZ;
  88.       __builtin_ia32_ldmxcsr (mxcsr);
  89.     }
  90. #else
  91.   unsigned int mxcsr = __builtin_ia32_stmxcsr ();
  92.   mxcsr |= MXCSR_DAZ | MXCSR_FTZ;
  93.   __builtin_ia32_ldmxcsr (mxcsr);
  94. #endif
  95. }
  96. #endif
  97.