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1 /*
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2 * Copyright (C) 2005, 2007, 2009 Free Software Foundation, Inc.
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3 *
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4 * This file is free software; you can redistribute it and/or modify it
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5 * under the terms of the GNU General Public License as published by the
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6 * Free Software Foundation; either version 3, or (at your option) any
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7 * later version.
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8 *
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9 * This file is distributed in the hope that it will be useful, but
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10 * WITHOUT ANY WARRANTY; without even the implied warranty of
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11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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12 * General Public License for more details.
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13 *
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14 * Under Section 7 of GPL version 3, you are granted additional
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15 * permissions described in the GCC Runtime Library Exception, version
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16 * 3.1, as published by the Free Software Foundation.
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17 *
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18 * You should have received a copy of the GNU General Public License and
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19 * a copy of the GCC Runtime Library Exception along with this program;
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20 * see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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21 * <http://www.gnu.org/licenses/>.
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22 */
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23
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24 #define MXCSR_DAZ (1 << 6) /* Enable denormals are zero mode */
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25 #define MXCSR_FTZ (1 << 15) /* Enable flush to zero mode */
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26
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27 #ifndef __x86_64__
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28 /* All 64-bit targets have SSE and DAZ;
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29 only check them explicitly for 32-bit ones. */
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30 #include "cpuid.h"
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31 #endif
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32
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33 static void __attribute__((constructor))
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34 #ifndef __x86_64__
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35 /* The i386 ABI only requires 4-byte stack alignment, so this is necessary
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36 to make sure the fxsave struct gets correct alignment.
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37 See PR27537 and PR28621. */
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38 __attribute__ ((force_align_arg_pointer))
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39 #endif
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40 set_fast_math (void)
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41 {
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42 #ifndef __x86_64__
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43 unsigned int eax, ebx, ecx, edx;
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44
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45 if (!__get_cpuid (1, &eax, &ebx, &ecx, &edx))
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46 return;
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47
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48 if (edx & bit_SSE)
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49 {
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50 unsigned int mxcsr = __builtin_ia32_stmxcsr ();
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51
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52 mxcsr |= MXCSR_FTZ;
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53
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54 if (edx & bit_FXSAVE)
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55 {
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56 /* Check if DAZ is available. */
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57 struct
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58 {
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59 unsigned short int cwd;
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60 unsigned short int swd;
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61 unsigned short int twd;
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62 unsigned short int fop;
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63 long int fip;
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64 long int fcs;
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65 long int foo;
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66 long int fos;
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67 long int mxcsr;
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68 long int mxcsr_mask;
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69 long int st_space[32];
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70 long int xmm_space[32];
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71 long int padding[56];
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72 } __attribute__ ((aligned (16))) fxsave;
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73
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74 __builtin_memset (&fxsave, 0, sizeof (fxsave));
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75
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76 asm volatile ("fxsave %0" : "=m" (fxsave) : "m" (fxsave));
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77
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78 if (fxsave.mxcsr_mask & MXCSR_DAZ)
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79 mxcsr |= MXCSR_DAZ;
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80 }
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81
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82 __builtin_ia32_ldmxcsr (mxcsr);
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83 }
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84 #else
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85 unsigned int mxcsr = __builtin_ia32_stmxcsr ();
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86 mxcsr |= MXCSR_DAZ | MXCSR_FTZ;
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87 __builtin_ia32_ldmxcsr (mxcsr);
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88 #endif
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89 }
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